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M‐currents in frog sympathetic ganglion cells: manipulation of membrane phosphorylation
Author(s) -
Chen Hsinyo,
Smith Peter A.
Publication year - 1992
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1992.tb14254.x
Subject(s) - muscarine , dephosphorylation , endocrinology , chemistry , medicine , adenosine , muscarinic acetylcholine receptor , biophysics , oxotremorine , adenosine triphosphate , phosphatase , phosphorylation , biochemistry , biology , receptor
Summary1 . The inward current and the M‐current ( I M ) suppression produced when muscarine is applied to frog sympathetic ganglion cells was recorded by means of the whole‐cell patch‐clamp technique. The holding potential was −30 mV and [K + ] o was 6 m m . 2 . The steady‐state I M was maintained for at least 20 min when the patch pipette contained neither adenosine 5′‐triphosphate (ATP) nor adenosine 3′:5′‐cyclic monophosphate (cyclic AMP). Inclusion of these substances or the ATP antagonst, β,γ‐methyleneadenosine 5′‐triphosphate (β,γ‐MethATP; 1 or 2 n m ) (failed to alter the rate of I M ‘run down’. By contrast, inclusion of adenosine‐5′‐O‐(3‐thiotriphosphate) (ATP‐γ‐S, 1 or 2 m m ) resulted in a 60% reduction of the current within 18 min. 3 . Despite the inability of ATP‐γ‐S to maintain steady‐state I M , it had no effect on the ability of muscarine (2–100 μ m ) to suppress a constant fraction of the available current. ATP‐γ‐S and β,γ‐MethATP increased the rise time and duration of the response to muscarine. 4 . Inclusion of a phosphatase inhibitor, diphosphoglyceric acid (DPG, 1–2.5 m m ) or alkaline phosphatase (100 μg ml −1 ) failed to affect the amplitude of muscarinic responses. 5 . These results question the role of the phosphorylation and/or dephosphorylation reactions in the transduction mechanism for muscarine‐induced I M suppression but are consistent with the possibility that M‐channels are ‘directly coupled’ via G‐protein to the muscarinic receptor.