A patch clamp study of muscarinic excitation of the rat adrenal chromaffin cells
Akaike, A.; Mine, Y.; Sasa, M.; Takaori, S.
Journal of Pharmacology and Experimental Therapeutics 255(1): 340-345
1990
ISSN/ISBN: 0022-3565 PMID: 2213565 Document Number: 350685
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 to cell-free patch recordings 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 in the present study had properties similar to those of the resting or muscarine-activated K+ currents 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.