[Calcium pooling by plasma and extra-plasma buffer systems: effects of prolonged hypokinesia]

Healthy test subjects were intravenously injected with calcium solutions during ambulatory activity and after 100-day exposure to head-down tilt. It was demonstrated that different mechanisms were involved in maintaining ionized calcium at a constant level and that their contribution changed after the tilt study. It was also shown that the capacity of extra plasma pool was decreased, kinetic characteristics of the Ca2+ binding reaction were modified, and responses of mineralotropic hormones to induced hypercalcemia were enhanced.