title: Metabolism of toad ventricle during alterations to the inotropic state.
abstract: 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.
authors.affiliation: Department of Physiology, Monash University, Clayton, Victoria, Australia.
authors.forename: P C
authors.initials: PC
authors.lastname: Dooley
authors.forename: I R
authors.initials: IR
authors.lastname: Wendt
mesh_terms: D000818:Animals; D001692:Biological Transport; D002021:Buffers; D002024:Bufo marinus / Q000502:physiology*; D002118:Calcium / Q000378:metabolism*; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D004734:Energy Metabolism; D006358:Hot Temperature; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009921:Metaproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010210:Papillary Muscles; D051381:Rats; D017207:Rats, Sprague-Dawley; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000378:metabolism; D013045:Species Specificity; D013314:Stress, Mechanical
chemical_list: D002021:Buffers; D012433:Ryanodine; C004717:diacetylmonoxime; D009921:Metaproterenol; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D003931:Diacetyl; D002118:Calcium