Age-related effects of acidosis in isolated cardiac muscle

Acidosis is associated with myocardial ischemia and several reports indicate the greater vulnerability of the aged heart to ischemic dysfunction. We investigated the effects of hypercapnic acidosis on isolated heart (n = 14) and papillary muscle (n = 10) from adult and senescent rats. Acidosis (pH from 7.36 to 6.91) induced a decrease in left ventricular developed pressure together with an increase in left ventricular end-diastolic pressure, but nias signifi cantly more evident in senescent than in adult hearts (p < .01). The return to normal pH induced a further increase in the end-diastolic pressure parallel to the development of arrhythmias that were greater in senescent than ill adult hearts. In isolated papillary muscle, acidosis confirmed its greater negative inotropic effect on senescent than adult muscles (p < .01), while intracellular sodium activity (a(Na)(i)) increased to a similar extent in both adult and senescent papillary muscles (p = NS), 5-(N,N-dimethyl)-amiloride hydrochloride (DMA), a specific inhibitor of Na+/H+ exchanger produced similar modification of tension and a:. in both adult and senescent muscles. When DMA was superfused in acidotic solution, the contractility Iras markedly compromised in senescent than ill adult muscles (p < .01), bur the a(Na)(i) modifications were similar in adult and senescent muscles (p = NS). Our results show that acidosis induced a greater reduction of contractility in senescent than in adult hearts. The similarity of contractility during DMA administration between adult and senescent muscle and of modifications of a(Na)(i) suggests that depression of contractility with acidosis may be related to pathophysiologic mechanisms other than the Na+/H+ exchanger.