The properties of carbachol-activated nonselective cation channels at the single channel level in guinea pig gastric myocytes.
We investigated the properties of carbachol (CCh)-activated nonselective cation channels (NSC(CCh)) at the single channel level in the gastric myocytes of guinea pigs using a magnified whole-cell mode or an outside-out mode. The channel activity (NPo) recorded in a magnified whole-cell mode increased with depolarization (from -120 to -20 mV) and had the half activation potential of -81 mV under the symmetrical 140 mM Cs+ condition. The single channel conductance depended upon the extracellular monovalent cations with the order of Cs+ (35 pS) > Na+ (25 pS) > Li+ (21 pS). The channel activities markedly diminished or disappeared when external Cs+ was replaced with Na+ or N-methyl-D-glucamate (NMDG+). With Cs+ and Na+ as external cations, the channel showed a monotonic increase in NPo with the increased mole fraction of Cs+ over Na+, and it had an intermediate conductance value in solution containing 67% Cs+ with 33% Na+. These data suggested that the extracellular monovalent cations regulate the whole-cell current of NSC(CCh) by modulating both the open state probability and the unitary conductance, and there is one binding site for the extracellular cations within the pore.
Kang
T M
TM
Department of Physiology, Sungkyunkwan University School of Medicine, Suwon, Korea.
Kim
Y C
YC
Sim
J H
JH
Rhee
J C
JC
Kim
S J
SJ
Uhm
D Y
DY
So
I
I
Kim
K W
KW
D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D002586:Cesium / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007473:Ion Channels / Q000819:agonists / Q000378:metabolism / Q000502:physiology*; D008094:Lithium / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D009130:Muscle, Smooth / Q000166:cytology / Q000502:physiology*; D018408:Patch-Clamp Techniques; D012964:Sodium / Q000378:metabolism; D013270:Stomach / Q000166:cytology / Q000502:physiology*
D007473:Ion Channels; D002586:Cesium; D002217:Carbachol; D008094:Lithium; D012964:Sodium