Acceleration of Ca(2+) repletion in the junctional sarcoplasmic reticulum and alternation of the Ca(2+)-induced Ca(2+)-release mechanism in hypertensive rat (SHR) cardiac muscle.
We estimated the time taken for a repletion of the junctional sarcoplasmic reticulum (JSR) Ca(2+) stores from a family of mechanical restitution curves after twitches of various magnitudes in the cardiac muscle of hypertensive rats (SHR), using a method described previously (Tameyasu et al. Jpn J Physiol. 2004;54:209-19), to evaluate abnormality in Ca(2+) handling by cardiac JSR in hypertension. We found no differences in contractility or in the time course of mechanical restitution between SHR and the controls (WKY) at 3 weeks of age. In comparison to WKY, 7- and 20-week-old SHR showed a greater rested state contraction (RST) and similar or smaller rapid cooling contracture, suggesting that their JSR contains a similar amount of Ca(2+) at saturation, but releases more Ca(2+) upon stimulation. The adult SHR and WKY showed similar mechanical restitution time courses, but the adults had longer pretwitch latencies. The function G(t) representing the time course of JSR Ca(2+) store repletion in adult SHR exceeded the WKY value at t < or = 0.5 s, but the function H(t) representing JSR [Ca(2+)] change corresponding to the mechanical restitution after RST was smaller in the adult SHR at t < or = 0.5 s, resulting in smaller H(t)/G(t) in adult SHR at t < or = 0.5 s. Deviations of G(t), H(t), and H(t)/G(t) from WKY were greater at 20 weeks than at 7. The results suggest an acceleration of JSR Ca(2+) store repletion and an alternation of the Ca(2+)-induced release of Ca(2+ )from the JSR in young adult SHR.
Tanaka
Midori
M
Department of Physiology, St Marianna University School of Medicine, Kawasaki, Japan. m2tanaka@marianna-u.ac.jp
Tameyasu
Tsukasa
T
D000375:Aging / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004195:Disease Models, Animal; D006973:Hypertension / Q000378:metabolism* / Q000503:physiopathology; D009200:Myocardial Contraction / Q000502:physiology; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D002118:Calcium