Key result
Iberiotoxin, a selective MaxiK channel inhibitor, significantly reduced the maximum relaxant response to isoprenaline in guinea-pig esophageal smooth muscle from 91.8% to 76.9% (P<0.01).
Why the study?
Does isoprenaline induce relaxation of guinea-pig esophageal smooth muscle via beta1-adrenoceptor coupling with MaxiK channels?
Does isoprenaline induce relaxation of guinea-pig esophageal smooth muscle via beta1-adrenoceptor coupling with MaxiK channels?
Absolute Event Rate: 76.9% vs 91.8%
p-value: p=<0.01
Beta1-adrenoceptors are substantially coupled with MaxiK channels to produce relaxation of esophageal smooth muscle in the guinea-pig, though to a lesser extent than beta2-adrenoceptors in tracheal smooth muscle.
Supports beta1-adrenoceptor–MaxiK coupling in guinea-pig esophageal relaxation; hypothesis-generating for human smooth-muscle pharmacology, no practice change.
The possible functional coupling between beta1-adrenoceptor and MaxiK channels which results in smooth muscle relaxation was examined in the guinea-pig esophageal muscularis mucosae. Isoprenaline-elicited relaxation of esophageal smooth muscle was confirmed to be mediated through beta1-adrenoceptors as the response was competitively antagonized by a beta1-selective antagonist atenolol with a pA2 value of 7.01. Iberiotoxin (IbTx, 10(-7) M), a selective MaxiK channel inhibitor, substantially diminished the relaxant response to isoprenaline. The extent of the MaxiK channel contribution to the relaxant response was 15-40% of the control response when estimated as the E50%-Emax responses to isoprenaline. The relaxation to isoprenaline was also attenuated by high-KCl (80 mM) to the same degree as the relaxant response generated in the presence of IbTx, and thus the estimated extent of the K+ channel contribution was 10-40%. These findings indicate that beta1-adrenoceptors are substantially coupled with MaxiK channels to produce relaxation of esophageal smooth muscle in the guinea-pig. Although MaxiK channels account for the contribution of K+ channels to the beta1-adrenoceptor-mediated relaxation in this smooth muscle preparation, their contribution seems to be less when compared to the beta2-adrenoceptor-mediated relaxation of tracheal smooth muscle.
No takes yet. Share an insight, caveat, or question.
Tanaka et al. (2004) studied Normal esophageal smooth muscle. Iberiotoxin vs. Control (absence of Iberiotoxin) was evaluated on Maximum relaxant response (Emax) to isoprenaline (p=<0.01). Iberiotoxin, a selective MaxiK channel inhibitor, significantly reduced the maximum relaxant response to isoprenaline in guinea-pig esophageal smooth muscle from 91.8% to 76.9% (P<0.01).
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: