M‐currents in frog sympathetic ganglion cells: manipulation of membrane phosphorylation

• Published in: British journal of pharmacology Vol. 105; no. 2; pp. 329 - 334
• Main Authors: Chen, Hsinyo, Smith, Peter A.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.02.1992; Nature Publishing
• Subjects: Adenosine nucleotides; adenosine‐5′‐O‐ (3‐thiotriphosphate); Animals; autonomic ganglia; Biological and medical sciences; Cell physiology; diphosphoglyceric acid; Diphosphoglyceric Acids - pharmacology; effects on; Fundamental and applied biological sciences. Psychology; ganglia; Ganglia, Sympathetic - physiology; In Vitro Techniques; Ion Channels - physiology; Membrane and intracellular transports; membrane currents; membrane proteins; Membranes - metabolism; Molecular and cellular biology; Muscarine - pharmacology; muscarinic receptor; M‐current; Nucleotides - metabolism; Phosphorylation; potassium channel; protein kinase; protein phosphatase; Rana pipiens; Receptors, Muscarinic - physiology; Second Messenger Systems - physiology; sympathetic nervous system; β,γ‐methyleneadenosine 5′‐triphosphate; Phosphorylation; Frog; Amphibia; Electrophysiology; Salientia; Ionic channel; Muscarine; Nervous ganglion; Vertebrata; Membrane transport; Animal; Inward current; Potassium; Sympathic nervous system
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.1992.tb14254.x

Summary 1 . The inward current and the M‐current (IM) 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 mm. 2 . The steady‐state IM 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 nm) (failed to alter the rate of IM ‘run down’. By contrast, inclusion of adenosine‐5′‐O‐(3‐thiotriphosphate) (ATP‐γ‐S, 1 or 2 mm) resulted in a 60% reduction of the current within 18 min. 3 . Despite the inability of ATP‐γ‐S to maintain steady‐state IM, it had no effect on the ability of muscarine (2–100 μm) 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 mm) 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 IM suppression but are consistent with the possibility that M‐channels are ‘directly coupled’ via G‐protein to the muscarinic receptor.