The release of calcium from cardiac mitochondria: the importance of the calcium-protein ratio.

Using a DW 2 dual wavelength spectrophotometer (AMINCO) and murexide as a Ca2+ sensitive indicator it is shown that guinea-pig heart mitochondria can release accumulated Ca2+ without the influence of non-physiological material. The main factor which decides if accumulated Ca2+ is spontaneously released is the Ca2+/mitochondrial-protein ratio. Under appropriate assay conditions a critical intramitochondrial Ca2+ concentration is reached. Increasing this concentration leads to Ca2+-release.