THE INFLUENCE OF CALCIUM ON THE CONTROL OF FLUID SECRETION IN THE COCKROACH SALIVARY GLAND

¹ Department of Veterinary Physiology, University of Edinburgh, Edinburgh EH9 IQH

When cockroach salivary glands are bathed in calcium-free medium the basal rate of fluid secretion increases from about 1 nl/min to about 10 nl/min; maintained dopamine stimulation elicits a further rise in secretory rate which gradually declines. Evidence is presented which indicates that magnesium is unable to substitute for calcium in this system. When calcium is returned to the bathing solution after a period of calcium deprivation there is a transient increase in secretory rate. Stimulation of the glands in certain conditions which inhibit the secretory response leads to some kind of calcium-dependent active state in the secretory cells which can outlast the interaction of the agonist with its receptors. It is concluded that stimulus-secretion coupling in this gland involves a calcium-dependent second messenger system.