Effects of potassium on membrane potential, spike discharge, and tension in taenia coli

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Abstract
The relationship between phasic and tonic responses, spike discharge, and membrane potential in taeniacoli of the guinea-pig in glucose-free, high-K medium was investigated using the sucrose-gap technique. High-K media (40-60 m[image]) caused a rapid rise of tension which gradually declined to a new steady-state level (tonic response). This was accompanied by membrane depolarization and the appearance of spike discharge. One to three minutes after adding K, spike frequency and amplitude gradually decreased, and by 3 min. all membrane activity ceased, the preparation remaining depolarized. In glucose-free media only a rapid rise and fall of tension occurred following addition of K to the medium. The changes in electrical properties were basically the same as in normal medium. In Ca-free solutions changes in electrical properties were similar to those seen following the application of K in normal Tyrode solution, but tension did not develop. It was concluded that tension response to K contains a phasic and tonic component. Evidence was discussed which suggested that the phasic response results from a release of tissue Ca probably by spike discharge and membrane depolarization. On the other hand, the tonic contracture results from a K-induced depolarization, the coupling between the two events being a metabolically dependent transmembrane transport of Ca.