Jpn. J. Pharmacol. 85 (3), 291-298 (2001)

The Properties of Carbachol-Activated Nonselective Cation Channels at the Single Channel Level in Guinea Pig Gastric Myocytes

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

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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