Properties of non‐junctional acetylcholine receptor channels on innervated muscle of Xenopus laevis.
- 1 May 1984
- journal article
- Published by Wiley in The Journal of Physiology
- Vol. 350 (1), 631-648
- https://doi.org/10.1113/jphysiol.1984.sp015222
Abstract
Patch-clamp recordings of current through acetylcholine-activated channels were made from non-junctional membrane of innervated myotomal muscle from Xenopus laevis. Two classes of acetylcholine (ACh) receptor channels were identified on the basis of current amplitudes. Both amplitude classes exhibited current-voltage relations which deviated from linearity as the extrapolated reversal potential was approached (-5 to -12 mV). Over the range of greatest linearity the conductances of the two classes were 64 and 44 pS. Both event classes were blocked by alpha-bungarotoxin. At the normal resting membrane potential (approximately -95 mV) the larger conductance channel (gamma) exhibited an apparent mean channel open time of less than 1 ms, compared to approximately 2 ms for the smaller gamma class. The apparent open time was voltage-dependent, changing e-fold with a 63 mV hyperpolarization for the high gamma channel and 93 mV hyperpolarization for the low gamma channel. At low ACh concentrations (0.1-0.3 microM) both amplitude classes exhibited bursts of successive openings separated by brief closures of less than 0.5 ms. Bursts were separated by longer closed intervals of 1 to greater than 100 ms. Closed interval histograms revealed corresponding populations of brief and long closures, indicating that at least two kinetic processes are required to describe the distribution of closed intervals. In the absence of exogenous ACh, channels were observed in an occasional patch which showed a conductance and extrapolated reversal potential similar to ACh-activated channels. In such patches the event frequency could occasionally be altered by adjusting the negative pressure applied to the patch. The two main conductance classes of ACh activated channels were observed to coexist in most patches. However, the most frequent event observed in non-junctional membrane of innervated muscle corresponded to the high gamma class. In this respect, the non-junctional ACh receptors bore a greater similarity to junctional ACh receptors than to non-junctional receptors reported for denervated muscle.Keywords
This publication has 23 references indexed in Scilit:
- Developmental changes in the distribution of acetylcholine receptors in the myotomes of Xenopus laevis.The Journal of Physiology, 1983
- Single acetylcholine-activated channels show burst-kinetics in presence of desensitizing concentrations of agonistNature, 1980
- Change in synaptic channel gating during neuromuscular developmentNature, 1978
- Acetylcholine-induced ionic channels in rat skeletal muscle.1978
- Development of the myotomal neuromuscular junction in Xenopus laevis: An electrophysiological and fine-structural studyDevelopmental Biology, 1977
- Junctional and extrajunctional acetylcholine receptors in normal and denervated frog muscle fibresPflügers Archiv - European Journal of Physiology, 1976
- Noise analysis of drug induced voltage clamp currents in denervated frog muscle fibres.The Journal of Physiology, 1976
- Single-channel currents recorded from membrane of denervated frog muscle fibresNature, 1976
- Fluorescent staining of acetylcholine receptors in vertebrate skeletal muscleThe Journal of Physiology, 1974
- The statistical nature of the acetylcholine potential and its molecular componentsThe Journal of Physiology, 1972