Figure 6. Cholinergic depolarization of PaS neurons is dependent in part on blockade of the muscarinic-dependent outward K⁺ current, I _M.

A. Bath application of CCh (50 µM) results in a significant inward current in cells held at −60 mV (*: p<0.05), and also occludes inward currents induced by the M-current blocker XE-991 (10 µM; black bar, compare with Fig. 5A). B. Membrane currents during slow voltage ramps from −120 mV to −40 mV in the presence of TTX (0.5 µM) and ZD7288 (50 µM), and during subsequent bath application of CCh (light grey line; 50 µM; B₁) show that cholinergic receptor activation induces an inward current at voltages near resting membrane potential that reverses around −76 mV, consistent the blockade of outward K⁺ currents. The application of CCh occluded additional inward current during subsequent bath application of XE-991 (dark grey line; 10 µM) suggesting that CCh depolarizes PaS neurons in part by suppression of the M-current. Current subtractions show that CCh blocks an outward current that reverses at −83.3±7.0 mV (black line; B₂), and also occluded membrane currents normally induced by XE-991 (grey line).