Contractility and 45Ca fluxes in heart muscle of flounder at a lowered extracellular NaCl concentration.
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+.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D005399:Fishes / Q000502:physiology*; D006321:Heart / Q000502:physiology*; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism; D009994:Osmolar Concentration; D012965:Sodium Chloride / Q000494:pharmacology
D012965:Sodium Chloride; D002118:Calcium