Effects of Temperature on the Duration and Velocity of Myocardial Contraction in Normal and Low Calcium Media

(5 figures) The increase in the strength of cardiac muscle contraction on lowering the temperature -- a rather unexpected phenomenon, which seemingly contradicts the common experience that a decrease of temperature inhibits the rate of reactions within the biological systems - has been known for a century and has repeatedly attracted the attention of physiologists (CYON, 1866 - cf. KRUTA, 1938). Recently KAUFMANN and FLECKENSTEIN (1965) reopened this question and demonstrated that the effect of temperature is causally related to the concentration of the extracellular calcium. They concluded that the positive inotropic effect of low temperature is mainly duc to prolongation of action potential, and assumed that the underlying mechanism is in morc Ca ions being made available for the Contractile process. It has recently been shown that the effect of change of temperature on the contractile force of isolated atrial strips has an immediate and a cuniulative component ( SUMBERA, KRUTA and BRAVENY, 1966) ; the stabilisation of the contractile response is a long lasting and complex process, which involves both duration and velocity of contraction. In this paper, primarily dealing with the immediate effect, an attempt is made to contribute to the problem which mechanisms participate in the positive inotropic effect of low temperature, employing the rccently described method of rapid change of temperature of the perfusion fluid (SUMBERA, KRUTA and BRAVENY, 1966).