Dopamine acutely decreases type 3 Na+/H+ exchanger activity in renal OK cells through the activation of protein kinases A and C signalling cascades

Dopamine D-1-mediated inhibition of Na+,K+-ATPase activity in opossum kidney (OK) cells involves the sequential activation of the adenylyl cyclase-protein kinase A (PKA) and the phospholipase C-protein kinase C (PKC) pathways [Am. J. Physiol. Renal Physiol. 282 (2002) F1084.]. The present study evaluated the signalling cascades involved in dopamine-mediated inhibition of Na+/H+ exchanger isoform 3 (NHE3) in OK cells. The transport kinetics displayed a simple Michaelis-Menten relationship for extracellular Na+ of 25 +/- 6 mM. Dopamine and the dopamine D-1-like receptor agonist SKF 38393 ((+/-)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol) inhibited NHE3 activity in a concentration-dependent manner; the dopamine D-2-like receptor agonist quinerolane was devoid of effect. The SKF 38393-mediated inhibition of NHE3 was prevented either by the dopamine D-1-like receptor antagonist SKF 83566 ((+/-)-7-Bromo-8-8-hydroxy-3 methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine; 1 muM), overnight treatment with cholera toxin (500 ng/ml), the PKA antagonist H-89 (N-(2-[p-bromocinnamylamino]ethyl)-5 isoquinolinesulfonamide hydrochloride; 10 muM), the PKC antagonist chelerythrine (1 muM), or the phospholipase C inhibitor U-73,122 (1-(6-[(17beta]-3-methoxyestra-1,3,5[10]-trien-17-yl) amino] hexyl)-1H-pyrrole-2,5-dione; 3 muM). In addition, dibutyril cAMP (dB-cAMP; 500 muM) was found to increase phospholipase C activity, both in membranes and in cytosol from OK cells; in contrast, phorbol-12,13-dibutyrate (PDB) (1 muM) did not have a significant effect on phospholipase C activity. Pretreatment of OK cells with the anti-G(s)alpha antibody, but not the anti-G(q/11)alpha antibody, blunted the inhibitory effect of SKF 38393 on NHE3 activity. It is concluded that dopamine D-1-mediated inhibition of NHE3 in renal 0 K cells involves both adenylyl cyclase-PKA and the phospholipase C-PKC pathways, a mechanism similar to that described for Na+,K+-ATPase. (C) 2004 Elsevier B.V. All rights reserved.