HYPOXIA AND CALCIUM

During hypoxia peak developed tension falls rapidly, resting tension inceeases slowly and recovery is incomplete if the hypoxia is sufficiently prolonged for resting tension to become greatly elevated. We propose that the initial fall of peak developed tension is due to a failure of excitation-contraction coupling at a time when high energy phosphate stores are only partially depleted. The rise of resting tension appears to reflect a deficiency of ATP necessary for the maintenance of intracellular calcium homeostasis. The removal of extracellular calcium, the addition of verapamil, and the measurement of calcium influx, indicate that the initial rise in resting tension is not due to an inward movement of calcium from the extracellular phase. Mechanical recovery after a period of hypoxia is jeopardized when there has been a substantial net gain of calcium. © 1979.