AGE-RELATED EFFECTS OF ACIDOSIS IN ISOLATED CARDIAC-MUSCLE

Acidosis is associated with myocardial ischemia and several reports in dicate the greater vulnerability of tile aged heart to ischemic dysfun ction. 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 vent ricular developed pressure together with an increase in left ventricul ar end-diastolic pressure, but nias signifi cantly more evident in sen escent than in adult hearts (p < .01). The return to normal pH induced a further increase in the end-diastolic pressure parallel to the deve lopment of arrhythmias that were greater in senescent than ill adult h earts. In isolated papillary muscle, acidosis confirmed ifs greater ne gative inotropic effect on senescent than adult muscles (p < .01), whi le intracellular sodium activity (a(Na)(i)) increased to a similar ext ent in both adult and senescent papillary muscles (p = NS), 5-(N,N-dim ethyl)-amiloride hydrochloride (DMA), a specific inhibitor of Na+/H+ e xchanger produced similar modification of tension and a:. in both adul t and senescent muscles. When DMA was superfused in acidotic solution, the contractility Iras markedly compromised in senescent than ill adu lt muscles (p < .01), bur tile a(Na)(i) modifications were similar in adult and senescent muscles (p = NS). Our results show that acidosis i nduced a greater reduction of contractility in senescent than in adult hearts. The similarity of contractility during DMA administration bet ween adult and senescent muscle and of modifications of a(Na)(i) sugge sts that depression of contractility with acidosis may be related to p athophysiologic mechanisms other than the Na+/H+ exchanger.