An insulin-stimulated cation channel in skeletal muscle. Inhibition by calcium causes oscillation.
A cation channel has been identified in the plasma membrane of skeletal muscle that oscillates open and closed in a regular manner. In an experimental system of patch-clamped reconstituted plasma membrane in phospholipid bilayers, the oscillations are calcium-dependent and constitute regular closing events due to inhibition of the channel by calcium with a Ki of 2.2 +/- 1 x 10(-6) M, followed by reopening. There are 3.7 +/- 1 calcium binding sites/channel. With sodium as the current vehicle, conductance is increased by voltage, insulin (Km = 5 +/- 0.6 x 10(-9) M), and hydrolyzable guanine nucleotides. Cyclic GMP alone with increase the conductance with a Km of 3.7 +/- 0.6 x 10(-7) M. In the absence of calcium, the unitary conductance with insulin + GTP or cGMP at 150 mM NaCl is 153 picosiemens. Sodium current is insensitive to 10(-5) M tetrodotoxin but inhibited by mu-conotoxin (Ki = 5 x 10(-8) M). These findings in the reconstituted system were verified in patch-clamped whole muscle cells where an insulin and cGMP-dependent sodium current inhibited by mu-conotoxin could be demonstrated. In the whole cell experiments, slow calcium-dependent oscillations of the sodium current were also detected.
Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, Massachusetts 02138.
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JE
McGeoch
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Guidotti
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002412:Cations; D002462:Cell Membrane / Q000502:physiology; D020916:Conotoxins; D006152:Cyclic GMP / Q000494:pharmacology; D004553:Electric Conductivity; D005583:Fourier Analysis; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D007473:Ion Channels / Q000187:drug effects*; D008051:Lipid Bilayers; D008564:Membrane Potentials; D009132:Muscles / Q000166:cytology / Q000187:drug effects*; D010456:Peptides, Cyclic / Q000494:pharmacology; D051381:Rats; D015222:Sodium Channels / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology
D002412:Cations; D020916:Conotoxins; D007328:Insulin; D007473:Ion Channels; D008051:Lipid Bilayers; D010456:Peptides, Cyclic; D015222:Sodium Channels; C046101:conotoxin GIII; D013779:Tetrodotoxin; D006160:Guanosine Triphosphate; D006152:Cyclic GMP; D002118:Calcium