B-2 KININ RECEPTOR UP-REGULATION BY CAMP IS ASSOCIATED WITH BK-INDUCED PGE(2) PRODUCTION IN RAT MESANGIAL CELLS

In the rat mesangial cell (MC), activation of the bradykinin B-2 recep tor (B2R) by bradykinin (BK) is associated with both phospholipase C ( PLC) and A(2) (PLA(2)) activities and with inhibition of adenosine 3', 5'-cyclic monophosphate (cAMP) formation leading to cell contraction. Because cAMP plays an important role in the regulation of gene express ion in general, we investigated the effect of increasing the intracell ular cAMP concentration ([cAMP](i)) in mesangial cells on the B-2 mRNA expression, on the density of B-2 receptor binding sites, on the BK-i nduced increase in both the free cytosolic Ca2+ concentration ([Ca2+]( i)), and in the prostaglandin E-2 (PGE(2)) production. Forskolin, PGE( 2), and cAMP analog, 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br cAMP), were used to increase [cAMP](i). Twenty-four-hour treatment wit h forskolin, PGE(2), and 8-BrcAMP resulted in significant increases in B-2 receptor binding sites, which were inhibited by cycloheximide. Th e maximum B-2 receptor mRNA expression (160% above control) was observ ed in cells treated during 24 h with forskolin and was prevented by ac tinomycin D. In contrast, the D-myo-inositol 1,4,5-trisphosphate (IP3) formation and the BK-induced increase in [Ca2+](i), reflecting activa tion of PLC, were not affected by increased levels of [cAMP](i). Howev er, the BK-induced PGE(2) release, reflecting PLA(2) activity, was sig nificantly enhanced. These data bring new information regarding the du al signaling pathways of B-2 receptors that can be differentially regu lated by cAMP.