Acceleration of Ca²⁺ repletion in the junctional sarcoplasmic reticulum and alternation of the Ca²⁺-induced Ca²⁺-release mechanism in cardiac muscle of hypertensive rat (SHR)

Abstract

We estimated the time course of the junctional sarcoplasmic reticulum (JSR) Ca²⁺ stores repletion from a family of the mechanical restitution curves after twitches of various magnitudes in cardiac muscle of hypertensive rat (SHR) using a method described previously , to evaluate abnormality in Ca²⁺ handling by cardiac JSR in hypertension. There were no differences in contractility nor the time course of mechanical restitution between SHR and control at 3 wks of age. 7 and 20 wk-old SHR showed a greater rested state contraction (RST) and a similar or smaller rapid cooling contracture compared to control, suggesting that their JSR contains a similar amount of Ca²⁺ at saturation and releases a greater amount of Ca²⁺ upon stimulation, compared to control. The adult SHR showed a similar time course of mechanical restitution to control, except a longer pretwitch latency in SHR than control. A function G(t) representing the time course of JSR Ca²⁺ stores repletion was greater in the adult SHR than control at t < 0.5 s, while a function H(t) representing JSR [Ca²⁺] change corresponding to the mechanical restitution after RST was smaller in the adult SHR than control at t < 0.5 s, resulting in smaller H(t)/G(t), in the adult SHR than control at t < 0.5 s. Deviation of G(t), H(t) and H(t)/G(t) from control were greater at 20 than 7 wks in SHR. The results suggest an acceleration of the JSR Ca²⁺ stores repletion and an alternation of the Ca²⁺-induced release of Ca²⁺ from the JSR in young adult SHR. [J Physiol Sci. 2008;58 Suppl:S188]