MICROFLUOROMETRIC STUDIES OF INTRACELLULAR CA2+ AND NA+ CONCENTRATIONS IN NORMAL HUMAN LABIAL GLAND ACINI

The responses of human labial salivary acini to muscarinic, adrenergic , and substance P peptidergic stimulation were studied using the fluor escent indicators fura 2 for intracellular Ca2+ concentration ([Ca2+]( i)) and sodium-binding benzofuran isophthalate for intracellular Naf c oncentration ([Na+](i)). Of the agents tested (carbachol, epinephrine, isoproterenol, and substance P) only the muscarinic agonist carbachol increased [Ca2+](i) substantially above basal levels (three to fourfo ld; half-maximal effect similar to 1 mu M). Experiments with the Ca2+- adenosinetriphosphatase inhibitor thapsigargin indicated the presence of both thapsigargin-sensitive and thapsigargin-insensitive intracellu lar Ca2+ stores, both of which were mobilized by carbachol. [Na+](i) i n resting labial acini was similar to 20 mM. On stimulation with carba chol, [Na+](i) rose transiently to more than three times this value an d then partially recovered. This carbachol-induced rise in [Na+](i) wa s largely blocked by bumetanide, a specific inhibitor of the Na+-K+-2C l(-) cotransporter. These results are consistent with an intact muscar inic fluid secretory response in human labial acini with transepitheli al Cl- secretion driven via Na+-K+-2Cl(-) cotransport and the secretio n of fluid presumably following Cl- loss via an apical Ca2+-dependent anion channel, as observed in salivary acini from other species.