[Mechanisms of change in the tonus of depolarized smooth muscle (guinea pig taenia coli) during application of a hyperpolarizing current].

Using double sucrose-gap technique three types of contractile responses of depolarized smooth muscle (guinea-pig taenia-coli) current-induced hyperpolarization were investigated: 1) contractions, 2) relaxations and 3) biphasic responses (relaxation followed by contraction). Every preparation generated generally only one type of responses (of different amplitude) when passing the currents of various strength. These responses were attributed to the changes of calcium fluxes through the cellular membranes under hyperpolarization. The phenomena observed were analysed on the mathematical model. Quantitative analysis showed that description of calcium current changes with equations of Hogkin-Huxley types was not sufficient; the model predicts the existence of non-inactivating channels in the smooth muscle cellular membrane. This very assumption allows to describe correctly all three types of cintractile responses.