Large-conductance calcium-activated potassium channels in neonatal rat intracardiac ganglion neurons
The properties of single Ca2+-activated K+ (BK) channels in neonatal rat intracardiac neurons were investigated using the patch-clamp recording technique. In symmetrical 140 mM K+. the single-channel slope conductance was linear 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 with the cytoplasmic free Ca2+ concentration ([Ca2+]i) with a Hill plot giving a half-saturating [Ca2+] (K0.5) of 1.35 μM and slope of ≅3. The BK channel was inhibited reversibly by external tetraethylammonium (TEA) ions, charybdotoxin, and quinine and was resistant to block by 4-aminopyridine and apamin. Ionomycin (1-10 μM) increased BK channel activity in the cell-attached recording configuration. The resting activity was consistent with a [Ca2+]i <100 nM and the increased channel activity evoked by ionomycin was consistent with a rise in [Ca2+]i to ≥ 0.3 μM. TEA (0.2-1 mM) increased the action potential duration 1.5-fold and reduced the amplitude and duration of the afterhyperpolarization (AHP) by 26%. Charybdotoxin (100 nM) did not significantly alter the action potential duration or AHP amplitude but reduced the AHP duration by 40%. Taken together, these data indicate that BK channel activation contributes to the action potential and AHP duration in rat intracardiac neurons.