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.
Hancock
S
S
Division of Basic Medical Science, Memorial University of Newfoundland, St. John's, Canada.
Moody-Corbett
F L
FL
Virgo
N S
NS
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