Acetylcholine activates a glibenclamide-sensitive K+ current in cat atrial myocytes

The preceding paper [Y. G. Wang and S. L. Lipsius, Am. J. Physiol. 268 (Heart Circ. Physiol. 37): H1313-H1321, 1995.] showed that when an atrial myocyte is treated with two consecutive exposures to acetylcholine (ACh) separated by a recovery interval, the second ACh exposure elicits a larger increase in K+ conductance than the first ACh exposure. In the present study a nystatin-perforated patch whole cell recording method was used to determine the mechanisms underlying the potentiating effect of ACh on ACh-induced K+ currents and the nature of the potentiated K+ current. The K+ current potentiated by the second ACh exposure was selectively abolished by 1) M1 muscarinic receptor block by 0.1 microM pirenzepine, 2) depletion of sarcoplasmic reticulum (SR) Ca2+ stores by 1 microM ryanodine or 10 mM caffeine, 3) intracellular dialysis with 10 mM ethylene glycolbis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA), 4) omitting external Ca2+, 5) 50% external Na+, 6) inhibition of protein kinase C by 0.01 microM staurosporine or 0.1 microM calphostin C, or 7) inhibition of ATP-sensitive K+ channels with 10 microM glibenclamide (Glib). AFDX-116 (100 microM), an M2 muscarinic receptor antagonist, selectively abolished the conventional ACh-activated K+ current and revealed an ACh-activated Glib-sensitive K+ current. In addition, with K+ conductances blocked and zero external Ca2+, 10 microM ACh induced a small nonselective inward current carried by Na+.(ABSTRACT TRUNCATED AT 250 WORDS)