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

Abstract

Experiments were carried out on isolated strips of guinea pig taenia coli under double sucrose gap conditions. The effect of papaverine on the kinetics of relaxation of polarized and depolarized smooth muscle was investigated after contraction induced by electrical stimulation. The depolarized muscle was stimulated by a long hyperpolarizing pulse and contraction developed as an off-response (OR). The experiments showed that: 1) the relaxation phase of OR of the depolarized muscle is more protracted than relaxation of spontaneous contractions of the muscle in Krebs' solution; 2) papaverine accelerates the relaxation phase of OR of the depolarized muscle; 3) papaverine in Krebs' solution does not accelerate the relaxation phase of induced contractions; 4) hyperpolarization and additional depolarization accelerate the relaxation phase of OR of the depolarized muscle; 5) hyperpolarization after preliminary treatment with papaverine does not accelerate the relaxation phase of OR of the depolarized muscle. It is suggested that slow electrically excitable calcium channels, blocked by papaverine, are present in the membrane of smooth-muscle cells. The flow of Ca through these slowly inactivated channels prolongs the descending phase of OR of the depolarized muscle.