Effects of muscarine on K(+)-channel currents in the C-cells of bullfrog sympathetic ganglion.
The effects of muscarine on small, putative C-cells and large, putative B-cells dissociated from bullfrog paravertebral sympathetic ganglia were studied by whole cell and single channel recording techniques. The dominant action of muscarine was to activate an inwardly-rectifying K+ current (IK(G)) in C-cells and to suppress M-current (IM) in B-cells. However, both IM and IK(G) were affected by muscarine in 5 out of 78 putative C-cells and in 8 others only IM was affected. By contrast, IK(G) was only activated in 1 out of 105 B-cells. This predicts that the muscarinic slow IPSP, which can be evoked by preganglionic stimulation, occurs exclusively in C-cells. 6% of these cells could, however, generate a muscarinic slow EPSP in addition to a slow IPSP and 10% could generate a slow EPSP without a slow IPSP. The rectification associated with IK(G) was neither a direct consequence of the direction of movement of K+ ions nor a simple consequence of channel block by intracellular Mg2+ or Na+ ions. The fit of the activation curve by a Boltzmann equation suggests that the conductance underlying IK(G) is controlled by a voltage-dependent gating charge (valency approximately -2). Muscarine activated no new channels in outside-out or cell-attached patches but increased the opening probability of two types of K+ channels (unitary conductances approximately 20 pS and approximately 55 pS). The possible role of these channels in the generation of IK(G) is discussed.
Kurenny
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DE
Department of Pharmacology, University of Alberta, Edmonton, Alta, Canada.
Chen
H
H
Smith
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PA
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects; D048429:Cell Size; D004553:Electric Conductivity; D005728:Ganglia, Sympathetic / Q000166:cytology / Q000187:drug effects*; D009116:Muscarine / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects*; D011892:Rana catesbeiana
D015221:Potassium Channels; D009116:Muscarine