Acetylcholine dose-response relation and the effect of cesium ions in the rat adrenal chromaffin cell under voltage clamp.

Acetylcholine(ACh)-induced inward current was examined in the rat adrenal chromaffin cell in culture. Cells were voltage clamped with one electrode using the giga-seal technique. The ACh dose-response relationship was determined by applying various concentrations of ACh with the "puffer" method. Although there were several technical difficulties, we found tentative figures as 135 to 480 microM for the dissociation constant and 1.2 to 1.4 for the Hill coefficient. External Cs ions had a depressing effect on the ACh response. Cs ions may slowly block ACh receptor channels from outside at the resting state. The ACh response in normal saline recorded with the Cs-filled electrode reversed the polarity at -7.1 mV. When the amplitude of ACh-induced current was plotted against holding membrane potential the curve showed strong rectification at the region more negative than the reversal potential. Between +10 and +30 mV there was a region of a negative slope. We discussed possible mechanisms for this characteristic I-V curve.