Kinetics of guinea pig taenia coli smooth muscle relaxation. Effect of papaverine and polarization

: Experiments were conducted on isolated strips of the guinea pig taenia coli by the double sucrose gap technique. The effect of papaverins on the relaxation kinetics of the polarized and depolarized smooth muscle after contractions induced by electric stimulation was investigated. Depolarized muscle was stimulated by long-lasting hyperpolarizing pulses; contraction arose in response to the termination of the current pulse (off-response). It was found that: 1) the relaxation phase of the depolarized muscle off-response was slowed down as compared with the relaxation phase of the spontaneous contractions in Krebs solution; 2) papeverine accelerates the relaxation phase of the off-response of the depolarized muscle; 3) papaverine does not accelerate the relaxation phase of the evoked contractions in Krebs solution; 4) hyperpolarization and additional depolarization accelerate the relaxation phase of the off-response of the depolarized muscle; 5) hyperpolarization does not accelerate the relaxation phase of the off-response of the depolarized papaverine-treated muscle. The data obtained suggest the existence of the slow electroexcitable calcium channels in the membrane of the smooth muscle cells blocked by papaverine. The calcium influx through these channels slows down the relaxation phase of the depolarized muscle off-response.