ATPase Activity and Ca2+ Interaction of Myofibrils and Sarcoplasmic Reticulum Isolated from the Hearts of Spontaneously Hypertensive Rats

ATPase activity of myofibrils and Ca2+ binding ability of sarcoplasmic reticulum isolated from the hearts of spontaneously hypertensive rats (OkamotoAoki strain, SHR) and normotensive Wistar rats (NR) were measured. Myofibrils isolated from both the hearts of SHR and NR showed essentially the same activity either in the absence or presence of Ca2+. On the other hand, Ca2+ activated ATPase activity of relaxed preparation of myofibrils from SHR was significantly lower than that from NRThe maximum Ca2+ binding capacity of sarcoplasmic reticulum (SR) from SHR (8.80±0.33nmoles/mg) was significantly lower than that from NR (11.95±0.55). Also, SR from SHR had significantly elevated Ca2+ activated ATPase activity (0.171±0.009μmoles/mg/min) compared with that of NR (0.100±0.009). Values were expressed as mean±s.e.m.Reduction of Ca2+ binding capacity of SR may result in increase of intracellular free Ca2+ concentration which probably be one of the important factor for muscle contraction. If the abnormal intracellular distribution of Ca2+ is associated with the smooth muscle of cardiovascular system, it would cause the increase of vascular resistance resulting in hypertension.