The Rapid Cooling Contracture of Toad Cardiac Muscles

Abstract

Summary The effect of rapid cooling on the mechanical activities of the cardiac muscles of the Japanese toad was examined. 1. The mechanical responses produced by rapid cooling (230•Ž) in both auricular and ventricular muscle preparations were composed of an immediate effect (phasic contraction) and a delayed effect (tonic contraction). The immediate effect was blocked by TTX, but the delayed effect was not affected by TTX and Mn. 2. The tonic contraction of the delayed effect produced by rapid cooling was potentiated in Na-deficient Ringer solution in which an equivalent amount of NaCl was substituted for Tris-Cl. The relationship between the relative tension of the delayed effect produced by rapid cooling and the ratio of [Ca2+]/[Na+]2 showed an S-shaped curve. 3. Generation of tension development of the delayed effect produced by rapid cooling was obviously dependent upon the extracellular Ca concentrations. There was an S-shaped relationship between the relative tension of the delayed effect and pCa in the extracellular medium. 4. In the test solution containing Ca less than pCa 8.0, no tension development of the delayed effect was observed. However, the rapid cooling contracture was strongly elicited by application of caffeine (caffeine-RCC). 5. The caffeine-RCC was also observed in the presence of 100 mM KCl. 6. From the results of the present study, it was considered that, even though the Ca influx was abolished, the contraction of the cardiac muscle could be produced by another mechanism, probably due to increase of myoplasmic Ca released by rapid cooling from the cell membrane itself and the sarcoplasmic reticulum. Since 1960, SAKAI et al. (1960, 1965 have studied the effect of rapid cooling on the mechanical responses of normal and T-tubules distrupted skeletal muscles in the presence of a subthreshold concentration of caffeine, and concluded

Caffeine Contracture in Frog Cardiac Muscle after Exposure to High Concentrations of Calcium

“…2 A-D The present study showed that caffeine induced contracture in frog cardiac muscle after exposure to Ca-rich solution. Like the cooling contracture of SAKAI and KURIHARA (1974) and the contracture presented by other authors (FOZZARD, 1977), the contracture was composed of initial transient and late sustained tensions. The initial tension in caffeine contracture observed here was similar to that in ferret heart muscle reported by CHAPMAN and LEOTY (1976), in the manner that it was transient and was little dependent on Ca concentration during caffeine application.…”

Effects of rapid cooling on mechanical and electrical responses in ventricular muscle of guinea‐pig.

“…of skeletal muscle fibres after treatment with a low concentration of caffeine (Kurihara et al 1984) further suggests that rapid cooling in cardiac muscle depends on Ca2+ release from the s.r. In amphibian cardiac muscles, rapid cooling initiates contracture in the presence of caffeine (Chapman & Ellis, 1974;Sakai & Kurihara, 1974). The fact that mammalian cardiac muscle has a different critical r.c.c.…”

Ouabain Potentiation of Rapid Cooling Contracture of Caffeinized Cardiac Muscles in Calcium Deprived Medium

“…Caffeine contracture is readily induced in a sodium free medium (14,15). When RCCC was elicited in a Na-free medium (the NaCl was totally replaced by K2SO4 or choline chloride) containing 1.8 mM Ca2+, the mechanical responses produced by rapid cooling in both caffeinized (1 mM) cat and frog ventricle muscles were composed of an immediate effect (phasic contracture) and a delayed effect (tonic contracture) as reported by Sakai and Kurihara (16). In the Ca-deprived medium, only a tonic contracture was elicited by rapid cooling, as shown in the present experiments.…”

“…RCCC in frog skeletal muscles (15) and rapid cooling contracture without caffeine (RCC) in cardiac muscles (16) have been studied by Sakai who concluded that the contractile mechanism in RCCC or RCC must be due to the mobilization of bound Ca from SR (frog skeletal muscles and guinea pig cardiac muscles) or cell membrane (bufo cardiac muscles).…”