FRACTIONAL CA2-RETICULUM ACTIVATES CA2+ ENTRY IN FRESHLY ISOLATED RABBIT AORTIC ENDOTHELIAL-CELLS( RELEASE FROM THE ENDOPLASMIC)

The purpose of the present investigation was to examine the correlatio n between rates of endoplasmic reticulum (ER) depletion and activation of store oper ated channels (SOC) in freshly isolated rabbit aortic e ndothelial cells. We investigated the effects of 10 mu M cyclopiazonic acid (CPA), 10 mu M ryanodine, and 10mM caffeine on the rate of Ca2depletion from the ER and on Ca2+ and Mn2+ influx using fura-2 fluores cence. We observed that the spontaneous loss of the ACh-sensitive pool is slow, Activation of ryanodine receptors (caffeine, ryanodine) or i nhibition of the ER Ca2+ pump (CPA) increased the rate of Ca2+ loss fr om the ACh-sensitive pool. CPA stimulated Mn2+ influx, while caffeine and ryanodine did not. Our results show non linear correlation between ER depletion and activation of divalent cation entry, In the case of CPA, less than 20% depletion of the ACh sensitive store was required f or full activation of SOC, while caffeine and ryanodine deplete over 5 0% of the ACh sensitive store without activating any influx. These dat a suggest that only a small compartment of the ER is involved in regul ation of Ca2+ entry. (C) 1997 Academic Press.