Extracellular Ca2+ decreases chloride reabsorption in rat CTAL by inhibiting cAMP pathway

The effect of activation of the Ca(2+)-sensing receptor on net Cl flux (J(Cl)) has been investigated on microperfused cortical (C) thick ascending limb (TAL) from rat kidney. Increasing bath Ca(2+) from 0.5 to 3 mM or adding 200 mu M of the specific Ca(2+)-sensing receptor agonist neomycin reduced basal as well as antidiuretic hormone (ADH)-stimulated J(Cl) by 27.7 +/- 5.0% and 25.9 +/- 4.1%, respectively. Jet remained unchanged in time control tubules. The effect of neomycin/Ca(2+) on J(Cl) was blocked by two protein kinase A inhibitors, H-9 or H-89, but not by a protein kinase C inhibitor, GF-109203X, regardless of whether ADH was present or not. Moreover, H-89 decreased basal Jet and prevented a further effect of 3 mM Ca(2+). When Jet was increased by 8-bromo-cAMP plus IBMX, no effect of 3 mM Ca(2+) was observed. Inhibitors of phospholipase Az and cytochrome P-450 monooxygenase failed to modify the effect of 3 mM Ca(2+), although these agents dampened significantly the inhibitory effect of bradykinin on medullary TAL. We conclude that extracellular Ca(2+) decreases basal and ADH-stimulated Cl reabsorption in CTAL by inhibiting the cAMP pathway, independently of protein kinase C or phospholipase A(2) stimulation.