Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 53, Issue 1 B42-B48, Copyright © 1998 by The Gerontological Society of America
Age-related effects of acidosis in isolated cardiac muscle
P Abete, P Ferrara, S Bianco, C Calabrese, C Napoli, F Cacciatore, N Ferrara and F Rengo
Istituto di Medicina Interna, Facolta di Medicina e Chirurgia, Universita degli Studi di Napoli Federico II, Naples, Italy.
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 was significantly 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 in adult
hearts. In isolated papillary muscle, acidosis confirmed its greater
negative inotropic effect on senescent than adult muscles (p < .01),
while intracellular sodium activity (aNai) 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 aNai in both adult
and senescent muscles. When DMA was superfused in acidotic solution, the
contractility was markedly compromised in senescent than in adult muscles
(p < .01), but the aNai 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 aNai suggests that depression of
contractility with acidosis may be related to pathophysiologic mechanisms
other than the Na+/H+ exchanger.
