A patch clamp study of muscarinic excitation of the rat adrenal chromaffin cells.
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.
Department of Pharmacology, Faculty of Medicine, Kyoto University, Japan.
A
A
Akaike
Y
Y
Mine
M
M
Sasa
S
S
Takaori
D000818:Animals; D002837:Chromaffin Granules / Q000502:physiology*; D005260:Female; D008564:Membrane Potentials / Q000187:drug effects; D009116:Muscarine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D011976:Receptors, Muscarinic / Q000502:physiology*; D013757:Tetraethylammonium Compounds / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D015221:Potassium Channels; D011976:Receptors, Muscarinic; D013757:Tetraethylammonium Compounds; D013779:Tetrodotoxin; D009116:Muscarine; D011188:Potassium