Ion transport systems in human labial acinar cells

Human labial acini were assayed for the presence of ion transport systems associated with salivary fluid secretion using microfluorometric methods; Na+-K+-Cl- cotransport and Na+/H+ exchange activities (determined by their bumetanide and amiloride sensitivities, respectively) were found at levels similar to 50% of those seen in similarly assayed rat parotid acini, but little, if any, Cl-/HCO3- exchange activity was observed. Also, when human labial acini were stimulated with the muscarinic agonist carbachol, little evidence of the intracellular acidification associated with HCO3- secretion by other salivary glands was found. Na+/H+ exchange activity in human labial acini was downregulated (similar to 40%) by beta-adrenergic stimulation and upregulated (approximately threefold) by muscarinic stimulation. In contrast, beta-adrenergic stimulation produced only a marginally significant increase in Na+-K+-Cl- cotransport activity, and muscarinic stimulation was without effect. We conclude that basolateral Na+-K+-Cl- cotransport appears to be the dominant mechanism driving Cl- secretion and thereby fluid secretion in this tissue.