Effect of ruthenium red on the Ca2+ and Sr2+ efflux from rat liver mitochondria: influence of nupercaine

Interaction of Sr2+ with Ca2+-induced Ca2+ release in mitochondria

Respiring rat liver mitochondria are known to spontaneously release the Ca2+ taken up when they have accumulated Ca2+ over a certain threshold, while Sr2+ and Mn2+ are well tolerated and retained. We have studied the interaction of Sr2+ with Ca2+ release. When Sr2+ was added to respiring mitochondria simultaneously with or soon after the addition of Ca2+, the release was potently inhibited or reversed. On the other hand, when Sr2+ was added before Ca2+, the release was stimulated. Ca2+-induced mitochondrial damage and release of accumulated Ca2+ is generally believed to be due to activation of mitochondrial phospholipase A (EC 3.1.1.4.) by Ca2+. However, isolated mitochondrial phospholipase A activity was little if at all inhibited by Sr2+. The Ca2+-release may thus be triggered by some Ca2+-dependent function other than phospholipase.

Na+/Ca2+ antiports in membranes of rat incisor odontoblasts

When incubated in the presence of Na+ ions, dissected rat incisor odontoblasts extruded Ca2+ ions, as detected by tetracycline fluorimetry. Also odontoblast mitochondria, obtained by subcellular fractionation and monitored by ion-specific mini-electrode technique, were found to extrude Ca2+ upon addition of Na+ ions. These findings demonstrate the presence of Na+/Ca2+ antiports in the odontoblast plasma membrane as well as in the odontoblast mitochondrial inner membrane. In addition, evidence was found for an ATP-dependent Ca2+ ion extrusion across the plasma membrane in these cells.