Effect of papaverine on tone and contractions of the depolarized smooth muscle of the guinea pig taenia coli

Experiments were carried out on isolated strips of guinea pig taenia coli. The smooth muscle was depolarized in a solution with high potassium concentration (120 mM KCl). The effect of papaverine (in concentrations of 10−5 to 3.10−5 g/ml) on the tone and off-response to a prolonged and strong hyperpolarizing current was investigated on the denervated muscle. Papaverine was found: 1) to abolish contractile responses to application of histamine, bradykinin, and acetylcholine; 2) to reduce the tone of the depolarized muscle and abolish the effect of an increase in the Ca++ concentration in the external medium on muscle tone; 3) to have no effect on the amplitude and velocity of the ascending phase of the off-response; 4) to accelerate the descending phase of the off-response. The following hypotheses are put forward to explain the result: 1) in the cell membrane there are chemically excitable calcium channels which are blocked by papaverine; 2) in the membrane there are calcium leakage channels responsible for the maintenance of tone and blocked by papaverine; 3) papaverine has negligible effect on electrically excitable calcium channels.