Ion transport in exocrine glands with reference to cystic fibrosis

Sammanfattning: Aspects of ion transport in rat submandibular gland acinar cells at the subcellular level, and the regulation of chloride secretion and calcium mobilization in cultured pig tracheal gland acinar cells were studied with reference to the disease cystic fibrosis.In adult rat submandibular gland acinar cells, both cholinergic and α-adrenergic stimulation induced efflux of K+ and of C1-, but the response was generally less with α-adrenergic stimulation. Little or no change in elemental distribution was observed in the acinar cells of new-born rats after cholinergic stimulation. A clear decrease in Ca content of the secretory granules in adult rat acinar cells was observed after cholinergic stimulation. Incontrast, α-adrenergic stimulation did not significantly affect the Ca concentration. IP3 receptors were localized by immunocytochemistry to the endoplasmic reticulum and to as yet unidentified structures in the apical cytoplasm.Cultured cells, derived from pig tracheal gland acinar cells, retained structural characteristics (microvilli, secretory granules and desmosomes) of in situ epithelia. Chloride secretion was induced in these cultured cells by stimulation with cholinergic, or α- or β-adrenergic agonists. CAMP-activated chloride secretion was blocked, but ionomycin-, ATP- and UTP-induced chloride secretion was not affected by pretreatment with cystic fibrosis transmembrane conductance regulator (CFTR) antisense oligodeoxynucleotide. Both ATP and UTP clearly upregulated [Ca2+]i. Pertussis toxin inhibited the calcium response to UTP, but did not change the response to ATP. Pretreatment with U107, a phospholipase C inhibitor, inhibited the calcium response to both ATP and UTP. Immunocytochemistry showed that in these cells, the IP3 receptor was localized in the cytoplasm.Our findings indicate 1) that freshly isolated submandibular acinar cells can serve as a suitable in vitro system for the study of ion transport mechanisms in the submandibular gland, that important ion transport systems required for the response are not present in the early stages of postnatal development of the glands, and that the secretory granule could serve as an intracellular calcium store under physiological conditions; 2) that the tracheal gland acinar cell culture system is suitable for studying aspects of ion and water transport by the airwayglands, that there are cAMP- and Ca2+-dependent intracellular pathways for C1- secretion in the airway gland cells, and that ATP and UTP activate calcium mobilization in the cultured cells predominantly via the G protein-phospholipase C-IP3 pathway.