Mucin release and calcium fluxes in isolated rat submandibular acini

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Abstract
A method is described for preparing isolated rat submandibular acini by collagenase digestion followed by mechanical dispersion. As assessed by Trypan Blue exclusion, phase contrast microscopy, ATP content and release of mucins and lactate dehydrogenase, the acini are morphologically and functionally intact. Secretory function of isolated acini was similar to that of intact tissue in terms of time-course, dose dependence and degree of stimulation of mucin release by adrenergic secretagogues. Mucin release was increased to the same extent (approximtely 3-4-fold) by either isoproterenol or noradrenaline [norepinephrine] at a maximally effective concentration (10 .mu.M). Stimulation of mucin release by isoproterenol (10 .mu.M), noradrenaline (10 .mu.M) or adrenaline [epinephrine] (10 .mu.M) was inhibited by propranolol (30 .mu.M) but not by phentolamine (30 .mu.M). Isoproterenol (10 .mu.M) increased both 45Ca2+ uptake and efflux from the acini, which represented a net release of Ca. However, there was a delay (approximately 10 min) in onset of stimulation of 45Ca2+ mobilization which was not apparent in isoproterenol stimulation of mucin release. Increases in intracellular Ca mobilization in response to a .beta.-adrenergic secretagogue do not trigger mucin secretion from rat submandibular acini.