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G‐protein control of voltage dependence as well as gating of muscarinic metabotropic channels in guinea‐pig ileum.
Author(s) -
Zholos A V,
Bolton T B
Publication year - 1994
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1994.sp020242
Subject(s) - biophysics , chemistry , muscarinic acetylcholine receptor , agonist , carbachol , patch clamp , medicine , endocrinology , receptor , biochemistry , biology
1. Voltage‐dependent properties of muscarinic receptor cationic current activated by carbachol in single smooth muscle cells have been studied using patch‐clamp recording techniques. Cells were obtained by enzymic digestion from the longitudinal muscle layer of guinea‐pig small intestine. 2. The inward cationic current showed a pronounced U‐shaped current‐voltage relationship (inward current negative). The relationship of cationic conductance to voltage could be described by a Boltzman distribution which was shifted 36 mV in the negative direction on the voltage axis by increasing fractional receptor occupancy (by increasing agonist concentration from 3 to 300 microM), and in the positive direction by desensitization during prolonged application of agonist. Cationic channels opened by low and high concentrations of carbachol at the same potential do not have identical properties. 3. Release of GTP within the cell, by flash photolysis of an inert caged precursor, had the same effect on the current‐voltage relationship as increasing receptor occupancy by the agonist. Release of GDP beta S by flash photolysis had the opposite effect. 4. These various results could be explained if cationic channel opening upon receptor activation required binding of at least one alpha‐GTP subunit, but the position of the activation curve on the voltage axis depended critically on the concentration of activated G‐protein alpha‐subunits in the cell.