Abstract
By analyzing the short-term mechanical restitution after twitches of various amplitudes in rat heart muscle, we have hypothesized that Ca2+ repletion in the junctional sarcoplasmic reticulum (JSR) occurs with a common Ca2+ content vs. time relationship after various degrees of JSR Ca2+ release and deduced a time course of Ca2+ repletion and a ratio of Ca2+ release/content in the JSR (T.Tameyasu et al, Jpn J Physiol,2004).Based on this hypothesis,we reported slower JSR Ca2+ repletion and smaller ratio of JSR Ca2+ release/content in heart muscle of adult spontaneously hypertensive rat(SHR) than control (WKY) in previous physiological meetings.We examined short-term mechanical restitution with ventricular papillary muscle of infant (3 wks-old) SHR and control to determine how and when functional impairment occurs in the SR of SHR heart muscle in the present study.There were little differences in the rate of JSR Ca2+ repletion nor the ratio of JSR Ca2+ release/content between the infant SHR and control.The result,taken together with previous ones, suggests that the slowing of JSR Ca2+ repletion and decrease of the ratio of JSR Ca2+ release/content initiates between ages of 3 to 7 wks in SHR and that the latter continues to decrease at least until 20 wks of age. [J Physiol Sci. 2007;57 Suppl:S205]
