In Langendorff-perfused rabbit hearts, hypoxia increased intracellular Na content to 34.9 meq/kg dry wt compared to 13.6 meq/kg in normoxic controls.
Hypoxia-induced Na uptake in the myocardium appears to result from increased entry via Na-H exchange rather than decreased extrusion, leading to secondary Ca accumulation.
Absolute Event Rate: 34.9% vs 13.6%
Historically, increase in cell Na content during ischemic and hypoxic episodes were thought to result from impaired ATP production causing decreased Na(+)-K(+)-ATPase activity. Here we report the results of testing the alternate hypothesis that hypoxia-induced Na uptake is 1) the result of increased entry, as opposed to decreased extrusion 2) via Na-H exchange operating in a pH regulatory capacity and that cell Ca accumulation occurs via Na-Ca exchange secondary to collapse of the Na gradient. We used 23Na-, 19F-, and 31P-nuclear magnetic resonance (NMR) to measure intracellular Na content (Nai), Ca concentration ( Cai), pH (pHi), and high-energy phosphates in Langendorff-perfused rabbit hearts. When the Na(+)-K(+)-ATPase was inhibited by ouabain and/or K-free perfusion, hearts subjected to hypoxia gained Na at a rate greater than 10 times that of normoxic controls during the first 12.5 min Nai increased from 7.9 +/- 5.8 to 34.9 +/- 11.0 (SD) meq/kg dry wt compared with 11.1 +/- 16.3 to 13.6 +/- 9.0 meq/kg dry wt, respectively. When normoxic hearts were acidified using a 20 mM NH4Cl prepulse technique, pHi rapidly fell from 7.27 +/- 0.24 to 6.63 +/- 0.12 but returned to 7.07 +/- 0.10 within 20 min, while Na uptake was similar in rate and magnitude to that observed during hypoxia (24.5 +/- 13.4 to 132.1 +/- 17.7 meq/kg dry wt). During hypoxia and after NH4Cl washout, increases in Cai were similar in time course to those observed for Na.(ABSTRACT TRUNCATED AT 250 WORDS)
Anderson et al. (1990) studied Myocardial hypoxia and acidification. Hypoxia vs. Normoxic controls was evaluated on Intracellular Na content (Nai) at 12.5 min. In Langendorff-perfused rabbit hearts, hypoxia increased intracellular Na content to 34.9 meq/kg dry wt compared to 13.6 meq/kg in normoxic controls.