Effects of thioproline on isolated guinea pig papillary muscles

The effects of thioproline (T) on the contractility, functional refractory period (FRP), automaticity and dose-response curves for isoproterenol as well as calcium were studied in guinea pig papillary muscles. T decreased the amplitude of contraction of papillary muscles dose-dependently. T and propranolol antagonized the inotropic effect of isoproterenol. The pA2 values were 3.67 and 8.05, respectively. T and verapamil antagonized Ca2+ in a non-competitive manner. The pD’2 values were 2.29 and 5.67, respectively. T prolonged the functional refractory period of papillary muscles, but exerted no effect on the excitability. The automaticity of papillary muscles was decreased when the concentration of T reached 7.5 mM.