Angiotensin II Signals to Phospholipase D in the Spontaneously Hypertensive and Wistar-Kyoto Rats by Pharmacologically Distinct Mechanisms
Angiotensin II (Ang II) differentially activates phospholipase D (PLD) in vascular smooth muscle from spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. We show that the Ang II concentration-response curve with regard to Ang II-induced PLD activity in preglomerular arteriolar smooth muscle cells (RASMCs) is shifted 10-fold to the left (SHR EC50 = 6.0 x 10-9 M and WKY EC50 = 7.2 x 10-8 M) indicating that PLD activation is hypersensitive to Ang II in SHR RASMCs. We hypothesize that this increase in PLD activity is due to a different signaling cascade in the SHR leading to increased activation of PLD. To examine this hypothesis, we systematically blocked, with pharmacological inhibitors and dominant negatives, all known pathways leading to PLD activation from a G-protein linked receptor (see figure). We observed that PLD activity in both the SHR and WKY RASMCs was inhibited by expression of a Rho A dominant negative, but only PLD activity in the SHR was sensitive to the ARF specific inhibitor Brefeldin A (BFA). Importantly, PLD activation in the SHR and WKY was not sensitive to expression of either an ARF 1 or ARF 6 dominant negative protein. This indicates that there is a different and novel BFA target in the SHR.