Membrane mechanisms of activating depolarized smooth muscle contraction (guinea pig small intestine) during exposure to physiologically active compounds

: The experiments were performed on the depolarized smooth muscle of taenia coli with the use of double sucrose-gap arrangement. Muscle contractions were induced by 1) application of hystamin or bradikynin; 2) rectangular long-lasting (10--20 s) pulses of hyperpolarizing current--the strong contraction appeared in response to the switching off the current (off-response). Both the on- and off-responses to the hyperpolarizing current recorded before, during and after hystamine (or bradikynin)-induced contration were, as a rule, very similar. Treatment of smooth muscle with local anaesthetics (procaine, trimecaine, QX-572) removed hystamine- and bradikynin-induced contrations and only decreased off-responses. The analysis of the data obtained suggested the existence of the independent electrically and chemically excitable systems (channels?) OF Ca2+ ion transport in the membrane of smooth muscle cells.