Angiotensin II Signaling to Phospholipase D in Renal Microvascular Smooth Muscle Cells in SHR

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Abstract
Angiotensin II (Ang II)–induced phospholipase D (PLD) activity is greater in aortic smooth muscle from spontaneously hypertensive rats (SHR) versus normotensive Wistar-Kyoto rats (WKY). Whether and how this signaling pathway is altered in preglomerular microvascular smooth muscle cells (PGSMCs), a cell type that may participate in genetic hypertension, is unknown. The goals of the present study were to determine in SHR and WKY PGSMCs the following: (1) whether Ang II induces PLD activity; (2) whether the effect of Ang II on PLD activity is greater in SHR; (3) which PLD isoform is stimulated by Ang II; (4) what signaling pathway mediates Ang II–induced PLD stimulation; and (5) whether the signaling pathways mediating Ang II–induced PLD activity are different in SHR and WKY. The EC 50 for Ang II–induced PLD stimulation in SHR was 10-fold lower than the EC 50 in WKY, and both were inhibited by L-158,805, an AT 1 antagonist. Inhibitors of phosphoinositol-3-kinase and protein kinase C did not block Ang II–induced PLD activity in SHR and WKY PGSMCs. Catalytically-inactive constructs of PLD2 and RhoA, but not PLD1, ADP ribosylation factor 1 (ARF1), ARF6, or ADP ribosylation factor nucleotide exchange factor (ARNO) blocked Ang II–induced PLD activity in SHR and WKY PGSMCs. Brefeldin A completely blocked Ang II–induced PLD activity in SHR but only slightly reduced Ang II–induced PLD activity in WKY PGSMCs. Therefore, we conclude that in PGSMCs, the effect of Ang II on PLD activity is (1) greater in SHR; (2) mediated by AT 1 receptors signaling to PLD2; (3) transduced primarily by Rho proteins; and (4) inhibited in SHR by brefeldin A.