The effect of hyperosmolality on the rate of heat production of quiescent trabeculae isolated from the rat heart.
- PubMed: 8972388
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.
Author-supplied keywords
The effect of hyperosmolality on the rate of heat production of quiescent trabeculae isolated from the rat heart.
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