Potassium inward rectifier and acetylcholine receptor channels in embryonicXenopus muscle cells in culture

Single inward rectifier K+ channels were studied in Xenopus laevis embryonic myocytes. We have characterized in detail the channel which is most frequently observed (Kir) although we routinely observe three other smaller current levels with the properties of inward rectifier K+ channels (Kir(0.3), Kir(0.5) and Kir(0.7)). For Kir, slope conductances of inward currents were 10.3, 20.3, and 27.9 pS, in 60, 120 and 200 mM [K+]o respectively. Extracellular Ba2+ blocked the normally high channel activity in a concentration-dependent manner (KA = 7.8 microM, -90 mV). In whole-cell recordings of inward rectifier K+ current, marked voltage dependence of Ba2+ block over the physiological range of potentials was observed. We also examined current rectification. Following step depolarizations to voltages positive to EK, outward currents through Kir channels were not observed even when the cytoplasmic face of excised patches were exposed to Mg(2+)-free solution at pH 9.1. This was probably also true for Kir(0.3), Kir(0.5) and Kir(0.7) channels. We then examined the possibility of modulation of Kir channel activity and found neither ATP nor GTP-gamma S had any effect on Kir channel activity when added to the solution perfusing the cytoplasmic face of a patch. Kinetic analysis revealed Kir channels with a single open state (mean dwell time 72 msec) and two closed states (time constants 1.4, 79 msec). These results suggest that the native Kir channels of Xenopus myocytes have similar properties to the cloned strong inward rectifier K+ channels, in terms of conductance, kinetics and barium block but does show some differences in the effects of modulators of channel activity. Furthermore, skeletal muscle may contain either different inward rectifier channels or a single-channel type which can exist in stable subconductance states.

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Characterization of Single Inward Rectifier Potassium Channels from Embryonic Xenopus laevis Myocytes

Chauhan-Patel

Spruce

1997

Journal of Membrane Biology

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Activity-dependent switch from synapse formation to synapse elimination during development of neuromuscular junctions

Herrera

Zeng

2003

J Neurocytol

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The embryonic development of neuromuscular junctions consists of two successive epochs, an early period marked by exuberant synapse formation and a later period marked by synapse elimination. In the frog muscles we have studied, myogenesis is protracted and overlaps the periods of synapse formation and elimination. Thus, the formative and regressive events of synaptic development do not occur in synchrony across different fibers in the muscle. We propose that local activity orchestrates a shift from synaptogenesis to synapse elimination at the level of single muscle fibers. We also present evidence that perisynaptic Schwann cells and the expression of ion channels in the sarcolemma play important roles in the development of neuromuscular junctions. Questions for future study are outlined.

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Potassium inward rectifier and acetylcholine receptor channels in embryonicXenopus muscle cells in culture

Cited by 2 publications

References 46 publications

Characterization of Single Inward Rectifier Potassium Channels from Embryonic Xenopus laevis Myocytes

Characterization of Single Inward Rectifier Potassium Channels from Embryonic Xenopus laevis Myocytes

Activity-dependent switch from synapse formation to synapse elimination during development of neuromuscular junctions

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