INTRACELLULAR CA2+ AND PKC ACTIVATION DO NOT INHIBIT NA+ AND WATER TRANSPORT IN RAT CCD

Experiments examined the effects of elevation of intracellular calcium concentration ([Ca2+]i) or activation of protein kinase C (PKC) on Na + and water transport in the rat cortical collecting duct (CCD). We me asured the lumen-to-bath Na-22+ flux (J1-->b), transepithelial voltage (V(T)), and water permeability (P(f)) in CCD from deoxycorticosterone (DOC)-treated rats. Ionomycin (.5 and 1 muM) and thapsigargin (1 and 2 muM) were used to increase [Ca2+]i. Phorbol 12-myristate 13-acetate (PMA; 0.3 and 1 muM) and oleoyl-acetyl-glycerol (OAG; 100 muM) were us ed as activators of PKC. [Ca2+]i was measured in isolated perfused tub ules using the fluorescent dye fura 2. When added to the bathing solut ion, 220 pM arginine vasopressin (AVP) failed to affect [Ca2+]i, where as 1 muM ionomycin increased [Ca2+]i by 103 +/- 15% and 2 muM thapsiga rgin increased [Ca2+]i by 24 +/- 4%. In flux studies, neither ionomyci n nor thapsigargin affected J1-->b or P(f), although ionomycin caused marked morphological changes. Ionomycin also failed to alter either pa rameter in tubules from non-DOC-treated rats. Neither 100 muM OAG nor 1 muM PMA affected J1-->b or P(f). OAG at 50 muM had no effect on V(T) or transepithelial resistance, indicating no inhibition of conductive Na+ transport. We conclude that increased [Ca2+]i and PKC activation do not affect J1-->b or P(f) in the rat CCD. These findings may accoun t for the sustained increase in J1-->b produced in the rat CCD by AVP.