INCREASED CALCIUM RELEASE FROM SARCOPLASMIC-RETICULUM STIMULATED BY INOSITOL TRISPHOSPHATE IN SPONTANEOUSLY HYPERTENSIVE RAT-HEART CELLS

It is known that inositol (1, 4, 5)-trisphosphate (IP3) stimulates Ca2+ release from sarcoplasmic reticulum (SR) in several tissues, but in cardiac myocytes this phenomenon has not been confirmed. The purpose of the present study was to confirm the effect of (1, 4, 5)-IP3 on Ca2+ release from SR in cardiac myocytes. The effect of IP3 on Ca2+ release from SR in hypertrophic cardiac cells was also determined. We examined the effects of IP3 on Ca2+ release from cardiac myocyte SR by the bigital-image method in a single cell. We also determined the effect of IP3 on calcium release from isolated SR. SR was prepared from spontaneous hypertensive rat hearts and Wistar kyoto rat hearts. The SR was prelabeled with Ca-45(2+), and then incubated with the indicated concentrations of Ip3 for 1 min at 37-degrees-C. In cardiac myocytes treated with saponin, Ca2+ release stimulated by 10 muM (1, 4, 5)-IP3 was detected by fura-2. In Ca-45(2+) prelabeled SR, the maximal Ca2+ release was achieved at 10 muM IP3 incubated for 1 min. The release of Ca2+ was higher in SR of SHR than in the SR of WKY. IP3 stimulates Ca2+ release from cardiac SR, and this release is greater in SHR than in WKY. However, it is uncertain whether this phenomenon plays a role in cardiac hypertrophy.