A patch clamp study of muscarinic excitation of the rat adrenal chromaffin cells

A Akaike, Y Mine, M Sasa and S Takaori

Department of Pharmacology, Faculty of Medicine, Kyoto University, Japan.

A patch clamp study was performed to determine the ionic mechanisms underlying the muscarinic excitation of rat adrenal chromaffin cells. Burst-like, single-channel currents with brief openings were recorded during cell-attached or cell-free patch recording when the pipette solution contained high K+ media (70-140 mM), and the currents were recorded at potentials near the resting membrane potential. The amplitude and frequency of channel openings were dependent on the membrane potential and the K+ concentration of the external medium. Moreover, the single-channel currents observed with high K+ outside the membrane during inside-out recording were suppressed by the addition of a K+ channel blocker, tetraethylammonium, inside the membrane. These results suggest that the single K+ currents recorded in the present study had properties similar to those of the resting or muscarine- activated K+ currents in atrioventricular cells of the rabbit heart. During cell-attached patch recording with the high K+ medium in the recording pipette, muscarine at concentrations of 10(-5) to 10(-4) M dose dependently decreased the frequency of the channel openings but did not affect the current-voltage relationship or the time constants of open and close time histograms. These results indicate that muscarinic-induced suppression of K+ currents is caused by a decrease in the number of active K+ channels at the resting membrane potential.

Volume 255, Issue 1, pp. 340-345, 10/01/1990
Copyright © 1990 by American Society for Pharmacology and Experimental Therapeutics