Fig. 7.

Voltage dependence of muscarinic-activated inward current. A, Carbachol current recorded with cesium gluconate-based intracellular solution in the presence of cesium (2 mm), barium (100 μm), cadmium (100 μm), and TTX (1 μm) at −40 mV. B, Hyperpolarizing voltage step commands from −40 to −120 mV (protocol represented inupper right traces) were applied before and during carbachol application. B, Net carbachol current tracings were obtained by subtracting the currents obtained in control conditions from those obtained during carbachol application. The instantaneous muscarinic current increases in amplitude with hyperpolarization. However, the hyperpolarizing steps also resulted in a fast outward relaxation, reflecting the voltage-dependent turning-off of the muscarinic current. C, Comparison of the instantaneous and steady-state I–V curves for the carbachol-induced current obtained from the cell represented inA. The holding current at −40 mV was 0.05 nA.