Studies of the contractility of mammalian myocardium at low rates of stimulation.

Abstract

1. Measurements have been made of tension development in papillary muscles isolated from the right ventricles of young cats. In some cases membrane potentials have also been recorded, using micro electrodes. 2. Regular contractions at a stimulation rate of 20 min(-1) (the 'standard' rate used in this study) had the following characteristics (30 degrees C): peak tension developed, about 43mN mm(-2); time to peak tension and time to 80% repolarization of the cell membrane, about 400 ms. 3. The corresponding figures for the first contraction after a rest of several minutes (rested state contraction) were: tension developed, about 4mN mm(-2); time to peak tension and time to 80% repolarization of the cell membrane, about 560 ms. Sometimes there was also an early peak in the mechanical response, about 250 ms after stimulation. 4. The time course with which tension development declined when the muscle was allowed to rest was examined under various conditions. It was found to decline more slowly when the muscle was potentiated by raising the bathing Ca2+ concentration and by stimulation at rates above 20 min(-1). 5. Tension development in rested state contractions was found to depend on the Ca2+ and Na+ concentrations in the bathing solution. The full effect of a change in either could be produced by exposing the resting muscle to the altered ionic conditions. 6. These experimental findings have been interpreted in terms of a simple model of the calcium movements involved in excitation-contraction coupling in the myocardial cell.

Proceedings of the Physiological Society, 25‐26 March 1986, University College London/Middlesex Meeting: Communications

“…1). Such a late maximum has been reported for heart muscle of the rat (Scriabine, 1959), and of the cat at high Ca2+ concentration or a high frequency of stimulation (Allen, Jewell and Wood, 1976).…”

Inotropic effects of Ca2+ channel agonist and antagonists in neuraminidase‐treated left atria of rats

“…We previously reported that the peculiar force-frequency relationship in rat atria was differently affected by aand P-adrenoceptor stimulation, especially at a higher range of stimulation rates (Hattori & Kanno, 1984). Complexly intertwined processes, sometimes acting in opposite directions, determine the actual tension developed at a constant stimulation rate (Chapman, 1979), and changing the stimulation interval may unmask a fundamental step ofcellular Ca2" dynamics (Allen et al, 1976;Edman & J6hannsson, 1976).…”

Postrest Contraction in the Ventricular Papillary Muscle of Spontaneously Diabetic WBN/Kob Rat.

“…In general, prolonged RI resulted in smaller T 1 /T ss . This phenomenon, which is known as "rest decay", reflects spontaneous leakage of Ca 2+ from SR [1,7,16]. "Rest decay" was seen in both non-diabetic and diabetic muscles (Fig.…”

“…Such a contraction is called a postrest contraction (PRC) or rested-state contraction [20]. However, the first contraction is larger than that of the steady-state contraction when stimulated after a short rest interval [1,3,5,11,23,24]. This potentiation of PRC is highly dependent on augmented Ca 2+ release from the sarcoplasmic reticulum (SR) [1,6,29].…”