Depressant effect of acetate in isolated cardiac tissue

Because acetate may have cardiodepressant properties in vitro, but previous studies have not separated out effects of acetate from possible effects of osmolality, sodium concentration, or calcium complexing, the effects of isosmotic acetate substitution (at a constant calcium concentration) on contractility were studied in isolated rat atrial tissue and in an isolated perfused non-working whole heart preparation. In spontaneously contracting right atrial tissue acetate induced dose dependent inhibition of isometric tension in the clinically important dose range of 4 to 16 mmol.litre-1. Bath acetate concentrations of 4, 16, or 64 mmol.litre-1 reduced peak tension (mean(SEM] to 78(2.7)%, 56(2.5)%, or 61(4.6)% respectively of control values. Because the calcium concentrations of the acetate baths were set equal to that of the control bath, calcium complexing by acetate could not have accounted for acetate's cardiodepressant effect. The inhibitory action was demonstrable with both isosmotic and hyperosmotic acetate solutions. Acetate had no effect on the spontaneous rate of atrial contraction. Inhibition of contractility (+dP/dt) by acetate in the whole heart preparation was also demonstrable at bath acetate concentrations of 8 and 16 mmol.litre-1. The results suggest that acetate has a myocardial depressant effect in vitro at concentrations achievable in the plasma during haemodialysis. The myocardial depressant action is not dependent on calcium complexing or on changes in bath osmolality or sodium concentration.