Post-transcriptional Control of Human maxiK Potassium Channel Activity and Acute Oxygen Sensitivity by Chronic Hypoxia

Various cardiorespiratory diseases (e.g. congestive heart failure, emphysema) result in systemic hypoxia and patients consequently demonstrate adaptive cellular responses which predispose them to conditions such as pulmonary hypertension and stroke. Central to many affected excitable tissues is activity of large conductance, Ca2+-activated K+ (maxiK) channels. We have studied maxiK channel activity in HEK293 cells stably co-expressing the most widely distributed of the human α- and β-subunits that constitute these channel following maneuvers which mimic severe hypoxia. At all [Ca2+]i, chronic hypoxia (∼18 mm Hg, 72 h) increased K+ current density, most markedly at physiological [Ca2+]i K+ currents in cells cultured in normoxia showed a [Ca2+]i-dependent sensitivity to acute hypoxic inhibition (∼25 mm Hg, 3 min). However, chronic hypoxia dramatically changed the Ca2+ sensitivity of this acute hypoxic inhibitory profile such that low [Ca2+]i could sustain an acute hypoxic inhibitory response. Chronic hypoxia caused no change in α-subunit immunoreactivity with Western blotting but evoked a 3-fold increase in β-subunit expression. These observations were fully supported by immunocytochemistry, which also suggested that chronic hypoxia augmented α/β-subunit co-localization at the plasma membrane. Using a novel nuclear run-on assay and RNase protection we found that chronic hypoxia did not alter mRNA production rates or steady-state levels, which suggests that this important environmental cue modulates maxiK channel function via post-transcriptional mechanisms. Various cardiorespiratory diseases (e.g. congestive heart failure, emphysema) result in systemic hypoxia and patients consequently demonstrate adaptive cellular responses which predispose them to conditions such as pulmonary hypertension and stroke. Central to many affected excitable tissues is activity of large conductance, Ca2+-activated K+ (maxiK) channels. We have studied maxiK channel activity in HEK293 cells stably co-expressing the most widely distributed of the human α- and β-subunits that constitute these channel following maneuvers which mimic severe hypoxia. At all [Ca2+]i, chronic hypoxia (∼18 mm Hg, 72 h) increased K+ current density, most markedly at physiological [Ca2+]i K+ currents in cells cultured in normoxia showed a [Ca2+]i-dependent sensitivity to acute hypoxic inhibition (∼25 mm Hg, 3 min). However, chronic hypoxia dramatically changed the Ca2+ sensitivity of this acute hypoxic inhibitory profile such that low [Ca2+]i could sustain an acute hypoxic inhibitory response. Chronic hypoxia caused no change in α-subunit immunoreactivity with Western blotting but evoked a 3-fold increase in β-subunit expression. These observations were fully supported by immunocytochemistry, which also suggested that chronic hypoxia augmented α/β-subunit co-localization at the plasma membrane. Using a novel nuclear run-on assay and RNase protection we found that chronic hypoxia did not alter mRNA production rates or steady-state levels, which suggests that this important environmental cue modulates maxiK channel function via post-transcriptional mechanisms. Crucial to the cellular and physiological response to acute perturbation of systemic and/or pulmonary O2 levels is the rapid inhibition of K+ channels by hypoxia (see Ref. 1Lopez-Barneo J. Pardal R. Ortega-Saenz P. Annu. Rev. Physiol. 2001; 63: 259-287Crossref PubMed Scopus (485) Google Scholar for recent review). Thus, acute modulation of ion channel activity is central to the homeostatic mechanisms that underlie chemosensing in carotid body (2Lopez-Barneo J. Lopez-Lopez J.R. Urena J. Gonzalez C. Science. 1988; 241: 580-582Crossref PubMed Scopus (453) Google Scholar, 3Buckler K.J. J. Physiol. 1997; 498: 649-662Crossref PubMed Scopus (261) Google Scholar, 4Peers C. Neurosci. Lett. 1990; 119: 253-256Crossref PubMed Scopus (253) Google Scholar), neuroepithelial body (5Youngson C. Nurse C. Yeger H. Cutz E. Nature. 1993; 365: 153-155Crossref PubMed Scopus (359) Google Scholar, 6Cutz E. Jackson A. Respir. Physiol. 1999; 115: 201-214Crossref PubMed Scopus (137) Google Scholar) (and its immortalized cellular counterpart, H146 cells, Ref. 7Hartness M.E. Lewis A. Searle G.J. O'Kelly I. Peers C. Kemp P.J. J. Biol. Chem. 2001; 276: 26499-26508Abstract Full Text Full Text PDF PubMed Scopus (109) Google Scholar) and (8O'Kelly I. Lewis A. Peers C. Kemp P.J. J. Biol. Chem. 2000; 275: 7684-7692Abstract Full Text Full Text PDF PubMed Scopus (71) Google Scholar, 9O'Kelly I. Stephens R.H. Peers C. Kemp P.J. Am. J. Physiol. 1999; 276: L96-L104PubMed Google Scholar, 10O'Kelly I. Peers C. Kemp P.J. Am. J. Physiol. 1998; 275: L709-L716PubMed Google Scholar, 11Peers C. Kemp P.J. Respir. Res. 2001; 2: 145-149Crossref PubMed Scopus (75) Google Scholar) systemic vascular smooth muscle (12Hulme J.T. Coppock E.A. Felipe A. Martens J.R. Tamkun M.M. Circ. Res. 1999; 85: 489-497Crossref PubMed Scopus (151) Google Scholar). Although somewhat controversial, ion channel inhibition has also been implicated in hypoxic vasoconstriction in the pulmonary circulation (13Ward J.P. Aaronson P.I. Respir. Physiol. 1999; 115: 261-271Crossref PubMed Scopus (114) Google Scholar). In addition, such O2 sensitivity is believed to play a significant role in modulation of excitability in several cellular components of the mammalian nervous system (14Vergara C. Latorre R. Marrion N.V. Adelman J.P. Curr. Opin. Neurobiol. 1998; 8: 321-329Crossref PubMed Scopus (632) Google Scholar, 15Coppock E.A. Martens J.R. Tamkun M.M. Am. J. Physiol. 2001; 281: L1-L8Crossref PubMed Google Scholar, 16Plant L.D. Kemp P.J. Peers C. Henderson Z. Pearson H.A. Stroke. 2002; 33: 2324-2328Crossref PubMed Scopus (71) Google Scholar, 17Jiang C. Haddad G.G. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 7198-7201Crossref PubMed Scopus (116) Google Scholar). Although O2-sensitive tissues express a wide variety of channel types, central to the cellular mechanism of acute O2 sensing in several is hypoxic suppression of large conductance Ca2+-activated K+ (maxiK) channels. Indeed, hypoxic inhibition of native maxiK channel activity has been demonstrated in carotid body (4Peers C. Neurosci. Lett. 1990; 119: 253-256Crossref PubMed Scopus (253) Google Scholar, 18Wyatt C.N. Peers C. J. Physiol. 1995; 483: 559-565Crossref PubMed Scopus (135) Google Scholar, 19Perez-Garcia M.T. Lopez-Lppez J.R. Riesco A.M. Hoppe U.C. Marban E. Gonzalez C. Johns D.C. J. Neurosci. 2000; 20: 5689-5695Crossref PubMed Google Scholar), pulmonary arteriolar smooth muscle (20Liu H. Moczydlowski E. Haddad G.G. J. Clin. Investig. 1999; 104: 577-588Crossref PubMed Scopus (88) Google Scholar), chromaffin cells (21Thompson R.J. Nurse C.A. J. Physiol. 1998; 512: 421-434Crossref PubMed Scopus (85) Google Scholar), and central neurons (20Liu H. Moczydlowski E. Haddad G.G. J. Clin. Investig. 1999; 104: 577-588Crossref PubMed Scopus (88) Google Scholar, 22Haddad G.G. Jiang C. Annu. Rev. Physiol. 1997; 59: 23-43Crossref PubMed Scopus (72) Google Scholar). Although their contribution to carotid body, chromaffin cell, and central neuronal function is well supported, some controversy still surrounds their involvement in pulmonary vasoconstriction (15Coppock E.A. Martens J.R. Tamkun M.M. Am. J. Physiol. 2001; 281: L1-L8Crossref PubMed Google Scholar) and there is good evidence for both delayed rectifier (23Tristani-Firouzi M. Reeve H.L. Tolarova S. Weir E.K. Archer S.L. J. Clin. Investig. 1996; 98: 1959-1965Crossref PubMed Scopus (104) Google Scholar) and tandem P domain K+ channels in the response (24Gurney A.M. Osipenko O.N. MacMillan D. Kempsill F.E. Clin. Exp. Pharmacol. Physiol. 2002; 29: 330-333Crossref PubMed Scopus (47) Google Scholar); the latter observation is fully supported by our recent reports of O2 sensitivity of the recombinant human tandem P domain channels, hTASK1 (25Lewis A. Hartness M.E. Chapman C.G. Fearon I.M. Meadows H.J. Peers C. Kemp P.J. Biochem. Biophys. Res. Commun. 2001; 285: 1290-1294Crossref PubMed Scopus (71) Google Scholar), and hTASK3 (26Kemp P.J. Lewis A. Miller P. Chapman C.G. Meadows H. Peers C. FASEB J. 2002; 16: A61Crossref PubMed Scopus (469) Google Scholar). Tissue specificity notwithstanding, we have recently demonstrated at the single channel level that a recombinant human maxiK channel can be rapidly and reversibly inhibited by acute hypoxia; this inhibition is underlain by hypoxia-evoked depression in unitary conductance, slowed channel activation kinetics (without an effect on channel deactivation kinetics), reduced open-state probability, and altered channel sensitivity to intracellular calcium concentration ([Ca2+]i) (27Lewis A. Peers C. Ashford M.L.J. Kemp P.J. J. Physiol. 2002; 540: 771-780Crossref PubMed Scopus (70) Google Scholar). Although it has been suggested that the mechanism of hypoxic regulation of K+ channels in general, and maxiK channels in particular, may modulation of cellular the of the is still and the mechanism inhibition of this channel in tissues Indeed, there reports that have suggested involvement of (e.g. 18Wyatt C.N. Peers C. J. Physiol. 1995; 483: 559-565Crossref PubMed Scopus (135) Google Scholar and H. Moczydlowski E. Haddad G.G. J. Clin. Investig. 1999; 104: 577-588Crossref PubMed Scopus (88) Google Scholar) or channel modulation (e.g. 17Jiang C. Haddad G.G. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 7198-7201Crossref PubMed Scopus (116) Google Scholar and 19Perez-Garcia M.T. Lopez-Lppez J.R. Riesco A.M. Hoppe U.C. Marban E. Gonzalez C. Johns D.C. J. Neurosci. 2000; 20: 5689-5695Crossref PubMed Google Scholar). In of regulation by cellular recent activation of these channels by in a recombinant cellular system H. M. H. J. Physiol. 2001; PubMed Scopus Google Scholar) and inhibition by reduced in neurons H. S. Neurosci. Lett. 2001; PubMed Scopus Google Scholar). However, we have that channel inhibition by hypoxia is in HEK293 cells stably the human channel (27Lewis A. Peers C. Ashford M.L.J. Kemp P.J. J. Physiol. 2002; 540: 771-780Crossref PubMed Scopus (70) Google Scholar). the of an of components with this channel for hypoxic inhibition human cells human cells a variety of cardiorespiratory diseases as chronic pulmonary of congestive heart failure, and adaptive the central of K+ channels to cellular it that of channel activity by or of hypoxia may to such as pulmonary hypertension (see J. Physiol. 2001; PubMed Scopus Google Scholar, Am. J. Respir. 2002; PubMed Scopus Google Scholar, P. Respir. Res. 2001; 2: PubMed Scopus Google Scholar for recent in to the well to C. Physiol. Rev. PubMed Scopus Google Scholar). a is supported by observations in chemosensing tissues such as the pulmonary K+ channel is in chronic Ref. P.I. Am. J. Physiol. 1994; Google Scholar) and the carotid body chronic hypoxia both in A. Jackson A. Nurse C.A. Proc. Natl. Sci. U. S. A. PubMed Scopus Google Scholar and A. Jackson A. Nurse C.A. J. Neurosci. 1995; PubMed Google Scholar and in C.N. C. D. Peers C. Proc. Natl. Acad. Sci. U. S. A. 1995; PubMed Scopus Google Scholar, G.J. J. Physiol. PubMed Scopus Google Scholar, G.J. J. Physiol. PubMed Scopus Google Scholar has been to the acute cellular and body hypoxic Thus, chronic hypoxia to be a central in responses both physiological and maxiK activity is in many tissues and maxiK activity is by we that of modulation by chronic hypoxia of the maxiK channel this we have studied the effect of severe hypoxia mm for 3 on channel and HEK293 cells stably co-expressing human that chronic hypoxia a on maxiK function is demonstrated by and which increased current density, altered Ca2+ sensitivity of acute O2 and of the β-subunit and augmented co-localization of the α- and β-subunits in the plasma membrane. cells, which express human channels D. P. Lett. 1997; PubMed Scopus Google Scholar), were in with and in a were in a of and α- and β-subunits were and HEK293 cells the α-subunit but in the of the β-subunit were also for of the cells were cultured for to 3 at in of mm Hg, chronic or mm Hg, all for were of the and were and with with Ca2+ to and 3 and in and with the in which changed were with were hypoxic by with for at to of no in or to the a E. J. Physiol. 1997; PubMed Scopus (109) Google Scholar); for the the were mm and mm were cultured for to 72 in or chronic hypoxic conditions to at for at to in a on the of a or an were at were on a were on a and of with an were and currents a were at and at to the A. PubMed Scopus Google Scholar) were and currents in HEK293 cells, were a to a single to single to for of the steady-state currents were the of the and current were the were the current the and current the of the as of current still at of as of the the were or as with of maxiK α- and β-subunits by of as with Ca2+ and and by in and to an and in a for for assay and with of and of a of for a and were by to were to at a of and with a maxiK channel α-subunit or of at a of In some the with this has with the in human of of for at of were to the level of maxiK in the chronic hypoxic cells as a of that found in the cells by the were on for 72 or chronic hypoxic cells were with mm and for with at were at were in and in mm and for 3 to were in of to of the maxiK in with the cells were by with in for in and with for a 3 were in of channel in the cells were in and in and for 3 cells were a in to and with a cells were in the that the were the in a of in all of HEK293 cells human channels were cultured in for 3 in or chronic hypoxic as were with and at for were in of mm 3 mm mm mm mm mm mm and and of to the mm mm mm mm mm mm and mm by on of a and were by for at at were in of mm mm mm mm mm and mm and at concentration by the of in a of a and J. 1997; PubMed Scopus Google Scholar, Am. J. Respir. Biol. 1997; PubMed Scopus Google Scholar) have a novel nuclear run-on on the we an of this or were and for at in mm mm mm mm and of mm of and were to no were to the the the the system In at for in a of with of on and to with the of a mm mm of and of were in a for at and the by at for with RNase at for were following the for were for the maxiK and β-subunits and specificity by and for the α-subunit were and and for the β-subunit were and were were in a of and were at at a concentration and the concentration to the concentration of which to with of conditions were as for by of and 72 with a of and a single of for with rates of and of α- and of the and chronic hypoxic conditions a by Res. 2001; 29: PubMed Scopus Google Scholar). were for on of HEK293 cells to the is the of the at concentration of (see and of by and and in single of the for both α- and β-subunits rates in normoxia and chronic hypoxia for is the in the the run-on in the or of and to human maxiK maxiK and human were as α-subunit α-subunit β-subunit β-subunit were and were to and of for the or were in with for or to the which as for were as and maxiK and for maxiK and for on were the in In of to a mm mm mm and of or of in a of In to the mm of to the to the activity of this were at for and by the of of and a at were by a following which the were and the by at in for protection cells following 3 chronic hypoxic or following the the protection assay In or of with maxiK and maxiK were also as were by and of and at for at by at for at were and in of were at for by an at of RNase in RNase and to of the and of the no RNase to the the were for at by the of of RNase were at for at by at for at the and in of were for 3 at and on a and at the the of the to for several Chronic maxiK currents in HEK293 cells stably co-expressing recombinant human maxiK channels the following in normoxia mm 72 h) or chronic hypoxia mm 72 were in the of [Ca2+]i to the levels in At all levels, chronic hypoxia caused an increase in current Chronic hypoxia no effect on with the a of and the chronic hypoxic a of in current in which the [Ca2+]i of currents the cultured in normoxia or chronic hypoxia. for these K+ channels, current this in a as [Ca2+]i an effect which in cells cultured in normoxia or hypoxia. the important [Ca2+]i chronic hypoxia evoked a large and significant in current density, at the and levels current were not altered Thus, the [Ca2+]i that supported hypoxic the physiological of this effect with by chronic hypoxia not at the In this of and of chronic hypoxia did not significant in current However, 72 to chronic hypoxia caused a significant to In HEK293 cells, at [Ca2+]i of current low and this not altered following 72 in chronic hypoxia These with cells which demonstrated current of and chronic at the of Thus, native currents of current and of chronic current to demonstrated single channels with a conductance of K+ the of maxiK channels, an which is with our in this (27Lewis A. Peers C. Ashford M.L.J. Kemp P.J. J. Physiol. 2002; 540: 771-780Crossref PubMed Scopus (70) Google Scholar). single channel were in native HEK293 cells not studied a to cells demonstrated no this In cells cultured for 72 in chronic hypoxia showed significant this in the of cells Chronic the Ca2+ of O2 the K+ currents and acute in mm to mm with [Ca2+]i to the of this effect of acute hypoxia and the that acute hypoxia to currents at this [Ca2+]i in cells in chronic hypoxia. with our which this (27Lewis A. Peers C. Ashford M.L.J. Kemp P.J. J. Physiol. 2002; 540: 771-780Crossref PubMed Scopus (70) Google Scholar), the recombinant human current cells cultured in normoxia showed a [Ca2+]i-dependent sensitivity to acute hypoxia Although this effect of acute hypoxia on currents to that demonstrated in the sensitivity of the system currents were inhibited by hypoxia at [Ca2+]i (see currents were inhibited by hypoxia at [Ca2+]i (see in Ref. A. Peers C. Ashford M.L.J. Kemp P.J. J. Physiol. 2002; 540: 771-780Crossref PubMed Scopus (70) Google Scholar). Thus, in cells with low [Ca2+]i, the maxiK current demonstrated or no acute hypoxic sensitivity acute hypoxic sensitivity increased at the [Ca2+]i Chronic hypoxia changed this of Ca2+ of the acute hypoxic response such that a inhibition of K+ current in response to acute hypoxia at low At [Ca2+]i, the cells cultured in chronic hypoxia demonstrated a sensitivity to acute hypoxia and there were no significant acute hypoxic inhibition the and chronic hypoxic chronic hypoxia increased the Ca2+ of the acute hypoxic response such that channel inhibition at low In to the cells co-expressing the α- and chronic hypoxia to increase current or acute hypoxic sensitivity in a HEK293 stably the α-subunit of the maxiK channel Thus, current density, at [Ca2+]i of following 72 in normoxia and following 72 in chronic hypoxia for Chronic a of the to the of the change in acute hypoxic sensitivity evoked by chronic we studied the effect of chronic hypoxia on maxiK α- and β-subunit levels Western blotting and 3 Western of cells cultured or chronic hypoxic Using an which for the a of the and there no significant the of this in to the β-subunit were of with a of of this which as a of in of on M. G.J. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: PubMed Scopus Google Scholar). that this to the β-subunit supported by the in which the of this following with the which the the not by this immunoreactivity of an of the β-subunit increased in the cells cultured in chronic hypoxia increase in β-subunit in response to chronic hypoxia by for the α- and β-subunits of maxiK In the cells, the α-subunit at the of the cells, with plasma intracellular also to In the cells cultured in chronic there no change in or of α-subunit the β-subunit in normoxia but following chronic hypoxia observation with the of β-subunit by Western blotting and and in and the α- and β-subunit immunoreactivity a increased co-localization of the in response to chronic hypoxia to Chronic of the a hypoxia caused an increase in β-subunit we the novel of nuclear run-on by to showed the of single at and for α- and β-subunit not specificity of the this single of the β-subunit with no in the an of a on a of α-subunit and with the β-subunit not to the of the found and with of of the were to the of α- and β-subunits as and which the for were for both α- and β-subunits on and chronic hypoxic a of caused a in to a the of with the to the of the nuclear run-on of the of mRNA following normoxia or chronic hypoxia showed no significant for of mRNA in the and chronic hypoxic were and for the α- and that chronic hypoxia did not alter rates of levels of mRNA of and were a protection assay and a were in the RNase maxiK and maxiK of in the with RNase of the were in all maxiK and maxiK of the to the of α- and β-subunits were to that of the the of the maxiK α- and β-subunit mRNA levels and chronic hypoxic significant in mRNA steady-state levels were for of the by the in and that chronic hypoxia mRNA of the maxiK of Chronic the of a mammalian recombinant our have demonstrated that acute hypoxia maxiK channels of in a to that in (27Lewis A. Peers C. Ashford M.L.J. Kemp P.J. J. Physiol. 2002; 540: 771-780Crossref PubMed Scopus (70) Google Scholar). However, in the the Ca2+ of the acute hypoxic response is the physiological [Ca2+]i has also demonstrated that chronic hypoxia in a significant of K+ current and in the Ca2+ sensitivity of the acute hypoxic response. this has important that that chronic hypoxic of maxiK function is to increase in β-subunit that is with co-localization of the β-subunit with the α-subunit at the plasma membrane. chronic hypoxia increased at the plasma is fully with the role of the β-subunit in channel Ca2+ Thus, a of the channels be to the β-subunit in their which a of channels with increased Ca2+ a channels to to acute hypoxia at In addition, chronic hypoxia in an increased of observation is with augmented of to the K+ current these it has been recently that of maxiK channels as the of α-subunit is increased J.P. J. Neurosci. 2002; PubMed Google Scholar). evidence that by chronic hypoxia is of the channel at the plasma is our observation that no such in cells the nuclear run-on demonstrate that is to regulation of maxiK channel function in this recombinant maxiK mRNA is not altered by chronic in the RNase protection no change in steady-state mRNA of this to the involvement of post-transcriptional in chronic hypoxic of maxiK channel function the of or mRNA in cells maxiK channels, there may well be regulation at the level of the and of maxiK a that has been suggested for chronic hypoxic regulation of in cells J. Biol. Chem. 1994; Full Text PDF PubMed Google Scholar). However, the of such mechanisms is we have been to that chronic via a mechanism that be of mRNA is to alter maxiK channel β-subunit as a Indeed, that the by 72 that the effect be by rapid for or of but is to an is with post-transcriptional regulation and there is evidence in the that in [Ca2+]i rates of but also the rates of for Ref. A. Biochem. J. 1999; PubMed Scopus Google Scholar). hypoxia-evoked regulation of has been and via of C. C. M. S. A. A. Biol. 2002; PubMed Scopus Google Scholar, M.E. M. Lett. 2001; PubMed Scopus Google Scholar), a mechanism that may be to that which we have for maxiK channel for of by Chronic channels widely distributed as of to many physiological J. Pardal R. Ortega-Saenz P. Annu. Rev. Physiol. 2001; 63: 259-287Crossref PubMed Scopus (485) Google Scholar). in of neuronal excitability (14Vergara C. Latorre R. Marrion N.V. Adelman J.P. Curr. Opin. Neurobiol. 1998; 8: 321-329Crossref PubMed Scopus (632) Google Scholar), chemosensing C. Pharmacol. Sci. 1997; Full Text Full Text PDF PubMed Scopus (88) Google Scholar, A.M. M.T. Gonzalez C. Lopez-Lopez J.R. Circ. Res. 2001; PubMed Scopus Google Scholar) of vascular R. G.J. M.T. Nature. 2000; PubMed Scopus Google Scholar, S. J. M. M. R. M. H. H. Circ. Res. 2000; PubMed Google Scholar). In of acute hypoxia result in modulation of and of via the of the carotid the neuroepithelial of the and the pulmonary J. Pardal R. Ortega-Saenz P. Annu. Rev. Physiol. 2001; 63: 259-287Crossref PubMed Scopus (485) Google Scholar, 6Cutz E. Jackson A. Respir. Physiol. 1999; 115: 201-214Crossref PubMed Scopus (137) Google Scholar, 11Peers C. Kemp P.J. Respir. Res. 2001; 2: 145-149Crossref PubMed Scopus (75) Google Scholar, 15Coppock E.A. Martens J.R. Tamkun M.M. Am. J. Physiol. 2001; 281: L1-L8Crossref PubMed Google Scholar). the that hypoxic inhibition of maxiK channels is central to some of these is evidence for mechanisms the in O2 in tissues recent Ref. 11Peers C. Kemp P.J. Respir. Res. 2001; 2: 145-149Crossref PubMed Scopus (75) Google Scholar) the modulation of the channel or by O2 is the most mechanism for native neuronal C. Haddad G.G. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 7198-7201Crossref PubMed Scopus (116) Google Scholar, S. C. A. Haddad Am. J. Respir. Biol. 2001; PubMed Scopus Google Scholar) and recombinant neuronal (27Lewis A. Peers C. Ashford M.L.J. Kemp P.J. J. Physiol. 2002; 540: 771-780Crossref PubMed Scopus (70) Google Scholar) maxiK channels. that regulation is of the most it that that can or a of these a for maxiK channel is the and that O2 such a Using our recombinant we have been to and post-transcriptional by chronic hypoxia have the evidence that chronic hypoxia the or of an ion channel is a observation the of or hypoxia in of chronic hypoxia that a of the is with hypertension and to vascular or P. Respir. Res. 2001; 2: PubMed Scopus Google Scholar). is to that for the increased of these patients to may of neuronal maxiK channels by this chronic such that to O2 at low [Ca2+]i in that is the cells to acute inhibition of these K+ channels be to an augmented response and of evidence suggests that of α-subunit at the plasma in cells cultured in normoxia is that of the a is the low Ca2+ which we and to the with the β-subunit and the of β-subunit in many is also in smooth muscle cells, for A. M. G.J. 1999; PubMed Scopus Google Scholar), that the cells which we be a for the of in that chronic in In we have the function of human maxiK channels is dramatically by chronic in environmental may underlie some of the which by chronic and hypoxia such as chronic pulmonary or congestive heart We for