Inward rectifier potassium current on embryonic Xenopus muscle cells at different times in culture.

Whole cell current recordings of Xenopus muscle cells in 1-day-old cultures revealed an inward K+ current, with properties similar to the inward rectifier of adult muscle. However, at the earliest ages (less than 10 h in culture) the time-dependent decline in the current amplitude, indicative of a depletion of extracellular K+, was not present. The change in the time-dependent decline of the current amplitude may result from a change in the channel itself or a change in the distribution of the channel in the membrane.