A signaling pathway for stimulation of Na+ uptake induced by angiotensin II in primary cultured rabbit [Olyctolagus cuniculus] renal proximal tubule cells

The aim of the present study was to examine the signaling pathways for a low does of angiotensin II (ANG II) on Na+ uptake of primary cultured rabbit renal proximal tubule cells (PTCs) in hormonally defined serum-free medium. The results were as follows ANG II (10(-11)M) stimulated the proliferation of PTCs, 10(-11)M ANG II stimulated Na+ uptake by 20%, whereas 10(-9)M ANG II inhibited it by 20% (p0.05). The stimulatory effect of 10(-11)M ANG II on Na+ uptake was inhibited by amiloride (10(-3)M) and by losartan (ANG II receptor subtype 1 antagonist, 10(-2)M) but not by PD123319 (ANG II receptor subtype 2 antagonist, 10(-8)M. Pertussis toxin (PTX, 50 ng/ml) prevented the ANG II-induced stimulation of Na+ uptake (p0.01). 8-Bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP, 10(-6)M) did not affect Na+ uptake. SQ22536 (adenylate cyclase inhibitor, 10(-6)M) also did not change the ANG II-induced stimulation of Na+ uptake. ANG II did not stimulate cAMP production. In contrast, 12-O-tetradecanoylphorbol-13-acetate (TPA, 0.01 ng/ml) produced significant increase in Na+ uptake. When ANG II and TPA were added together to the PTCs, there was no additive effect on Na+ uptake. Staurosperine (calcium-dependant protein kinase C inhibitor, 10(-6)M) led to a complete inhibition of ANG II-induced stimulation of Na+ uptake ANG II-treatment resulted in a 25% increase in total protein kinase C (PKC) activity. However, 10(-11)M ANG II did not change Ca2+]i mobilization and H3]-AA release while 10(-9)M ANG II increased both of them. In conclusion, the PTX-sensitive PKC pathway may be the main signaling cascade in the stimulatory effects of low dose of ANG II (10(-11)M) on Na+ uptake in the primary cultured rabbit renal proximal tubule cells in hormonally defined serum-free medium