1390 Intracellular Calcium Transients in Myocardium From Spontaneously Hypertensive Rats During the Transition to Heart Failure

To investigate the mechanism of impaired myocardial function after long-term pressure overload, we studied cardiac muscle mechanical contraction and intracellular calcium transients using the bioluminescent indicator aequorin. Left ventricular papillary muscle preparations were examined from three groups of rats: 1) aging spontaneously hypertensive rats (SHR) with clinical and pathological evidence suggesting heart failure (SHR-F group), 2) age-matched SHRs with no evidence of heart failure (SHR-NF group), and 3) age-matched normotensive Wistar-Kyoto rats (WKY group). Isometric force development was depressed in both SHR groups relative to theWKY group. Resting [Ca2'] i was lower in the SHR-F group, and the time to peak [Ca2"]; was prolonged in this group. The relative increases in peak [Ca'+]j with the inotropic interventions of increased [Ca2`1 and the addition of isoproterenol were similar