Ca2+-uptake and -release phenomena from cardiac mitochondria under normal and ischemic conditions.

Guinea-pig and dog heart mitochondria were isolated in a KEA-medium. Ca2+-transport across mitochondrial membranes was measured continuously with an Aminco Dual-Wavelength-Spectrophotometer and murexide as a Ca2+-sensitive indicator. Ischemia was produced by cardioplegia at 15 degrees C according to Bretschneider. Guinea-pig heart mitochondria as well as mitochondria from dog heart show a spontaneous Ca2+-release without nonphysiological influence. Addition of 3.5 M Na+ can induce a very quick release of Ca2+ taken up by heart mitochondria. This release is different from that occurring spontaneously. Progressive ischemia results in a marked depression of Ca2+-uptake and spontaneous Ca2+-release.