title: The effect of hyperosmolality on the rate of heat production of quiescent trabeculae isolated from the rat heart.
abstract: We have measured the rate of heat production of isolated, quiescent, right ventricular trabeculae of the rat under isosmotic and hyperosmotic conditions, using a microcalorimetric technique. In parallel experiments, we measured force production and intracellular calcium concentration ([Ca2+]i). The rate of resting heat production under isosmotic conditions (mean +/- SEM, n = 32) was 100 +/- 7 mW (g dry wt)-1; it increased sigmoidally with osmolality, reaching a peak that was about four times the isosmotic value at about twice normal osmotic pressure. The hyperosmotic thermal response was: (a) abolished by anoxia, (b) attenuated by procaine, (c) insensitive to verapamil, ouabain, and external calcium concentration, and (d) absent in chemically skinned trabeculae bathed in low-Ca2+ "relaxing solution." Active force production was inhibited at all osmolalities above isosmotic. Passive (tonic) force increased to, at most, 15% of the peak active force developed under isosmotic conditions while [Ca2+]i increased, at most, 30% above its isosmotic value. We infer that hyperosmotic stimulation of resting cardiac heat production reflects, in large part, greatly increased activity of the sarcoplasmic reticular Ca2+ ATPase in the face of increased efflux via a procaine-inhibitable Ca(2+)-release channel.
authors.affiliation: Laboratorium voor Fysiologie, Vrije Universiteit, Amsterdam. ds.loiselle@auckland.ac.nz
authors.forename: D S
authors.initials: DS
authors.lastname: Loiselle
authors.forename: G J
authors.initials: GJ
authors.lastname: Stienen
authors.forename: C
authors.initials: C
authors.lastname: van Hardeveld
authors.forename: E T
authors.initials: ET
authors.lastname: van der Meulen
authors.forename: G I
authors.initials: GI
authors.lastname: Zahalak
authors.forename: J
authors.initials: J
authors.lastname: Daut
authors.forename: G
authors.initials: G
authors.lastname: Elzinga
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002151:Calorimetry; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006652:Histological Techniques; D006358:Hot Temperature; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D007537:Isometric Contraction; D008297:Male; D009206:Myocardium / Q000378:metabolism; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology; D010100:Oxygen / Q000494:pharmacology; D051381:Rats
chemical_list: D010042:Ouabain; D010100:Oxygen; D002118:Calcium