Tong Mook Kang1, Young Chul Kim2, Jae Hoon Sim2,
Jong Chul Rhee3, Sung Joon Kim1, Dae Yong Uhm1,
Insuk So2,* and Ki Whan Kim2
1Department of Physiology and 3Department of Medicine,
Sungkyunkwan University School of Medicine, Suwon 440-746, Korea
2Department of Physiology and Biophysics, Seoul National University
College of Medicine, 28 Yongon-Dong, Chongno-Gu, Seoul 110-799, Korea
*Corresponding author. FAX: +82-2-763-9667
E-mail: insuk@plaza.snu.ac.kr
Abstract: We investigated the properties of carbachol (CCh)-activated
nonselective cation channels (NSCCCh) 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 NSCCCh by modulating
both the open state probability and the unitary conductance, and there is
one binding site for the extracellular cations within the pore.
Keywords: Nonselective cation channel, Single channel, Carbachol, Gastric
smoothmuscle
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