Inhibitors of arachidonic acid metabolism have variable effects on calciumsignaling pathways

The metabolic pathways of arachidonic acid (AA) have been shown to be impor tant in the regulation of cellular function. Several studies have demonstra ted both direct and indirect effects of products of these pathways in the r egulation of vascular actions, and in particular on signaling pathways. Bec ause intracellular calcium concentration is a significant mediator of stimu lus-coupled signal transduction, we investigated the effects of AA pathway inhibitors on angiotensin II (Ang II)-induced calcium mobilization in cultu red rat vascular smooth muscle cells (VSMC). Thus, specific calcium pools w ere examined for differential effects resulting from inhibitors of the thre e major pathways of AA metabolism. Inhibition of lipoxy-genase (LO) with 2. 5 mu mol/L of 5,8,11 eicosatriynoic acid (ETI), cyclooxygenase (CO) with 2 mu mol/L of ibuprofen (IBU), and cytochrome P-450 (P450) with 1 mu mol/L of 7-ethoxyresorufin (7ER) all reduced total Ang II-induced intracellular cal cium transients ([Ca2+](i)) in fura 2-loaded cultured rat VSMC. However, th e sites of action affected were unique for each inhibitor. Pretreatment of VSMC with either ETI or IBU inhibited thapsigargin (TG) (I mu mol/L)-sensit ive calcium increments (control; 118.0 +/- 33.1 nmol/L, n = 9, ETI; 34.7 +/ - 4.8 nmol/L, n = 9, IBU; 40.3 +/- 8.8 nmol/L, n = 8, P < .05 v control). B oth caffeine (CAF) and ryanodine (RY) treatment attenuated Ang II-induced [ Ca2+](i); however, pretreatment with ETI, IBU, or 7ER did not alter this ef fect. In other studies, the LO inhibitor ETI attenuated Ang II-induced Ca2 influx, whereas inhibitors of CO and P450 pathways had no effect. These da ta show that 1) ETI and IBU affect TG-sensitive Ca pools; 2) ETI, but not I BU nor 7ER, inhibited calcium influx; and 3) ETI, IBU, and 7ER affect simil ar intracellular calcium stores as CAF and RY. Thus, agonist-specific diffe rences in the effects of LO, CO, and P450 inhibition on vascular actions ma y be due to site-specific effects of these inhibitors on calcium mobilizati on. (C) 2001 American Journal of Hypertension, Ltd.