Potassium inward rectifier and acetylcholine receptor channels in embryonic Xenopus muscle cells in culture.
Embryonic muscle cells of the frog Xenopus laevis were isolated and grown in culture and single-channel recordings of potassium inward rectifier and acetylcholine (ACh) receptor currents were obtained from cell-attached membrane patches. Two classes of inward rectifier channels, which differed in conductance, were apparent. With 140 mM potassium chloride in the electrode, one channel class had a conductance of 28.8 +/- 3.4 pS (n = 21), and, much more infrequently, a smaller channel class with a conductance of 8.6 +/- 3.6 pS (n = 7) was recorded. Both channel classes had relatively long mean channel open times, which decreased with membrane hyperpolarization. The probability of finding a patch of membrane with an inward rectifier channel was high (66%) and many membrane patches contained more than one inward rectifier channel. The open state probability (with no applied potential) was high for both inward rectifier channel classes so that 70% of the time there was a channel open. Seventy-three percent of the membrane patches with ACh receptor channels (n = 11) also had at least one inward rectifier channel present when the patch electrode contained 0.1 mu M ACh. Inward rectifier channels were also found at 71% of the sites of high ACh receptor density (n = 14), which were identified with rhodamine-conjugated alpha-bungarotoxin. The results indicate that the density of inward rectifier channels in this embryonic skeletal muscle membrane was relatively high and includes sites of membrane that have synaptic specializations.
Division of Basic Medical Science, Memorial University of Newfoundland, St. John's, Canada.
S
S
Hancock
F L
FL
Moody-Corbett
N S
NS
Virgo
D000818:Animals; D002478:Cells, Cultured / Q000502:physiology / Q000648:ultrastructure; D004553:Electric Conductivity; D004594:Electrophysiology; D004625:Embryo, Nonmammalian / Q000166:cytology; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000166:cytology; D015221:Potassium Channels / Q000502:physiology*; D011950:Receptors, Cholinergic / Q000502:physiology*; D014982:Xenopus laevis / Q000502:physiology*
D015221:Potassium Channels; D011950:Receptors, Cholinergic