| pubmed-article:7869396 | pubmed:abstractText | The heat produced by toad ventricle during manipulations of the inotropic state was measured using thermopiles, and some comparisons made to rat ventricle. The tension-independent heat, peak stress, and the tension-dependent heat increased when [Ca2+]o increased from 0.25 to 2 mM in Ringer. In 2 mM [Ca2+]o, tension-independent heat, peak stress, and tension-dependent heat were 3.1 +/- 0.4 mJ/g, 38.4 +/- 5.5 mN/mm2, and 0.49 +/- 0.06 units; about 25% of the tension-independent heat may relate to the Na(+)-K+ pump. At similar [Ca2+]o, rat ventricle produced a smaller tension-independent heat (1.6 +/- 0.2 mJ/g), and active heat per unit stress (0.22 +/- 0.01 units) than toad. Tension-independent heat, stress, and tension-dependent heat were increased by orciprenaline, and decreased by BDM. Ouabain increased the stress and tension-dependent heat but not the tension-independent heat. Five millimolar [Ca2+]o in HEPES buffer decreased the stress but increased the tension-dependent heat compared to 2 mM [Ca2+]o in Ringer. Ryanodine and CPA caused major reductions in force and tension-independent heat in rat, but had little effect on toad ventricle. In conclusion, our results suggest that in toad ventricle (a) the sarcoplasmic reticulum plays only a minor role in activation and relaxation, (b) the Na(+)-K+ pump contributes substantially to activation metabolism, (c) active metabolism is stimulated by increases in [Ca2+]o and (d) there is a larger tension-independent heat, a larger active metabolism per unit stress, and a lower basal metabolism than in rat papillary muscle. The energy cost of removing intracellular Ca2+ through the sarcolemma appears to be greater than uptake into sarcoplasmic reticulum. | lld:pubmed |
