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Journal of Experimental Biology, Vol 109, Issue 1 201-207, Copyright © 1984 by Company of Biologists

JOURNAL ARTICLES

Contractility and 45Ca fluxes in heart muscle of flounder at a lowered extracellular NaCl concentration

H Gesser and A Mangor-Jensen

The twitch force of isolated electrically paced ventricular strips of flounder, Platichthys flesus L., increased after lowering the extracellular sodium chloride concentration by 50 mmol l-1. This response was markedly reduced by replacing the sodium chloride with either Tris-HCl or sucrose, so that osmolarity was unchanged. The 45Ca efflux decreased and the 45Ca influx increased when the extracellular sodium concentration Nao+ was lowered. In contrast, changing only the osmolarity had no observable effect on these fluxes. An increased resting tension appeared in strips exposed to a Na+-, Ca2+-free solution. This was transient at an unchanged osmolarity but became permanent at an osmolarity lowered by 100 mosmol l-1. These results suggest that both a lowered Nao and a lowered osmolarity have a positive inotropic effect, due respectively to an increased cellular uptake of Ca2+ and a redistribution of cellular Ca2+.




© The Company of Biologists Ltd 1984