Secretory response of dispersed rat submandibular cells. II. Mucin secretion

The secretory response of dispersed rat submandibular cells as it relates to the secretion of D-[1-14C]glucosamine hydrochloride-labeled mucin following sympathomimetic and parasympathomimetic stimulation was evaluated. The adrenergic agonists (-)-norepinephrine and (-)-epinephrine were found to have equal efficacy and potency with a median effective concentration (EC50) of 7.1 x 10(-7) M. (-)-Isoproterenol was found to be acting as a "partial" agonist and had an EC50 of 3.9 x 10(-7) M. (-)-Phenylephrine addition resulted in a small, but significant, secretion of mucin at higher doses tested (10(-4) M--10(-3) M). Neither cholinergic nor alpha-adrenergic receptor stimulation was able to elicit a net increase in the secretion of mucin. However alpha-adrenergic receptor activation in conjunction with beta-adrenergic receptor activation facilitated the rate of secretion. Extracellular Ca2+ and Mg2+ were not required for the secretion of mucin, but extracellular Ca2+ enhanced the rate of secretion following alpha- and beta-adrenergic receptor activation. However extracellular Ca2+ did not enhance mucin secretion following beta-adrenergic receptor activation. Both cellular Ca2+ and beta-adrenergic receptor activation were required to elicit a secretory response following sympathomimetic stimulation.