Parallel secretion of secretory proteins and calcium by the rat parotid gland

Abstract

The secretion of amylase, deoxyribonuclease, ribonuclease, protein and Ca 2+ by the rat parotid gland in vitro was studied. Isoproterenol and carbamoylcholine elicited a parallel discharge of amylase, deoxyribonuclease, ribonuclease and protein over a 40 min time period. The composition of the secretion was independent of the secretogogue used for stimulation. When gland slices from the same animal were stimulated with isoproterenol, adrenaline, phenylephrine or carbamoylcholine, secretory enzymes and protein were secreted in constant proportions. 45Ca injected intraperitoneally 16 h before stimulation with either isoproterenol or carbamoylcholine was released in parallel with amylase and protein. The relative proportions of amylase, ribonuclease, deoxyribonuclease, protein and Ca present in isolated parotid gland secretory granules was identical to that of isoproterenol stimulated gland secretion. It is concluded that the secretory proteins and Ca 2+ are discharged in constant proportions by the rat parotid gland regardless of the mode of stimulation or the rate of secretion. The similarity in the composition of gland secretion and granule contents also suggests that enzymes and Ca 2+ are released by exocytosis and not by diffusion across the apical plasma membrane.