Generation of a rapid step in the temperature of a papillary muscle.

Abstract

A fast temperature jump method is described for the study of electromechanical properties of an isolated papillary muscle of the rabbit heart. Arguments are given that such a temperature jump can be best obtained by joule heating using an alternating current with a frequency in the shortwave region. For the measurement of the fast increasing temperature and the achieved temperature distribution two types of thermometer are used with a response time shorter than a few ms and a high spatial resolution. No self heating of the thermometers due to induced currents was detected. Electrical disturbance in the signals representing temperature, Transmembrane potential and force of contraction were negligible immediately after the fast temperature increase as well as during the following steady-state temperature elevation. The inhomogeneity of the temperature increase in the muscle appeared to be about 30 per cent. In response to a temperature increase of 4°C in 30 ms the action potential shortens in about 3 s and the force of contraction decreases within one beat. From the results it can be concluded that fast changes in electromechanical properties of heart muscle after a fast temperature increase induced by a high-frequency alternating current are measurable and have physiological relevance.