Large-conductance calcium-activated potassium channels in neonatal rat intracardiac ganglion neurons

The properties of single Ca2+-activated K+ (BK) channels in neonatal rat in tracardiac neurons were investigated using the patch-clamp recording techni que. In symmetrical 140 mM K+, the single-channel slope conductance was lin ear in the voltage range -60/+60 mV. and was 207+/-19 pS. Na+ ions were not measurably permeant through the open channel. Channel activity increased w ith the cytoplasmic free Ca2+ concentration ([Ca2+],) with a Hill plot givi ng a half-saturating [Ca2+] (K-0.5) of 1.35 muM and slope of congruent to3. The BK channel was inhibited reversibly by external tetraethylammonium (TE A) ions, charybdotoxin, and quinine and was resistant to block by 4-aminopy ridine and apamin. Ionomycin (1-10 muM) increased BK channel activity in th e cell-attached recording configuration. The resting activity was consisten t with a [Ca2+](i) <100 nM and the increased channel activity evoked by ion omycin was consistent with a rise in [Ca2+](i) to <greater than or equal to >0.3 muM TEA (0.2-1 mM) increased the action potential duration congruent t o1.5-fold and reduced the amplitude and duration of the afterhyperpolarizat ion (AHP) by 26%. Charybdotoxin (100 nM) did not significantly alter the ac tion potential duration or AHP amplitude but reduced the AHP duration by co ngruent to 40%. Taken together, these data indicate that BK channel activat ion contributes to the action potential and AHP duration in rat intracardia c neurons.