The influence of calcium on the secretory response of the submaxillary gland to acetylcholine or to noradrenaline

Abstract

A wide variety of glands are known to be under nervous control and are stimulated to secrete by neurohumours such as acetylcholine (ACh) and the catecholamines, but little is known of the way in which these neurohumours evoke secretion. It has recently been suggested that ACh stimulates the adrenal medulla by causing the chromaffin cells to take up calcium, and that the appearance of free calcium in the cells then elicits the secretory response. This idea that calcium is a vital link in the process of 'stimulus-secretion coupling' at the adrenal gland arose mainly from experiments showing that catecholamine secretion varies with extracellular calcium concentration over a wide range and that calcium itself is a secretogogue in conditions known to lead to increased permeability of cell membranes (Douglas & Rubin, 1961); it has gained support from the finding that ACh greatly increases 45Ca uptake by the adrenal medulla (Douglas & Poisner, 1961, 1962 a).The question obviously arises whether the role of calcium at the adrenal medulla is unique or whether calcium may also be intimately involved in other secretory processes, particularly those which are likewise initiated by ACh. Among the many glands responding to ACh the adrenal medulla is, of course, exceptional: it is an endocrine gland and its secretory chromaffin cells are derived from the neural crest and are thus related to neurones; moreover, it secretes catecholamines, whereas the secretions of the cholinoceptive exocrine glands consist chiefly of water, electrolytes and protein; and, finally, the ACh 'receptors' of the chromaffin cells are nicotinic rather than muscarinic in type. In spite of these differences, there are certain similarities between the above two types of glands, which suggest the possibility of a common secretory mechanism. Thus the secretion of catecholamines by the chromaffin cells and the secretion of protein by exocrine cells such as the pancreas or salivary glands have certain morphological features in common. In each instance the secretory product is * Post-Doctoral Fellow, United States Public Health Service.

Loss of Hyperpolarization-activated Cl− Current in Salivary Acinar Cells from Clcn2 Knockout Mice

“…It is likely that the Ca 2ϩ -dependent Cl Ϫ channel is targeted to the apical membrane in parotid acinar cells as has been shown in pancreatic acinar cells (22). Because salivation is Ca 2ϩ -depend-ent (23)(24)(25), the Ca 2ϩ -gated Cl Ϫ channel has been predicted to be the primary Cl Ϫ channel activated during stimulated secretion. Additional Cl Ϫ channels found in salivary gland cells include those that are volume-sensitive (26), cAMP-dependent (18), hyperpolarization-activated (2,19), and channels with properties like ClC-0 (18).…”

Does somatostatin inhibition of insulin secretion involve two mechanisms of action?

“…Calcium ion (Ca2+) is essential for insulin secretion (5), as it is for many other secretory processes (6). Increasing Ca2+ concentration increases the amount of insulin released in response to a glucose stimulus during both the first and second phases of secretion by the isolated perfused rat pancreas (1,5).…”

Gastric Secretion in Hyperparathyroid Subjects before and after Parathyroid Surgery

“…Calcium certainly plays some r61e in the gastric secretion. The importance of the calcium ion in the secretory response to exogenous acetylcholine was demonstrated by Douglas & Rubin (1961) and Douglas & Poisner (1963). It has been suggested by Nordgren et al (1973) that this mechanism is counteracted by thyrocalcitonin by reducing the available calcium necessary for the release or effect of acetylcholine in the secretory mechanism.…”