Growth of the mitochondrial inner membrane in synchronous cultures of Tetrahymena pyriformis: an examination of phospholipid accumulation.

Based on morphological evidence, mitochondrial inner membrane growth has been reported to be discontinuous in heat shock-synchronized Tetrahymena pyriformis. As a biochemical measure of membrane growth under these conditions, we have examined phospholipid accumulation in the cell. No marked modulation of the accumulation of any of the major phospholipids could be detected through the cell cycle. At least 89% of the cardiolipin in the cells is restricted to the mitochondria, and we have used it as a marker for the growth of the mitochondrial inner membrane. During the heat shock synchrony, cardiolipin accumulates uniformly in parallel with the exponential rate of increase of total cellular phospholipids. These results suggest that at least the phospholipid component of all membrane systems in the cell grow continuously and uniformly. Additionally, we have shown that the total phospholipid content of Tetrahymena increases by a factor of 2.4 per generation following a series of heat shocks. No such net overaccumulation is observed for protein content.