Arachidonic acid inhibits hormone-stimulated cAMP accumulation in the medullary thick ascending limb of the rat kidney by a mechanism sensitive to pertussis toxin

Abstract

The possible regulation of adenosine 3',5'-cyclic monophosphate (cAMP) accumulation by arachidonic acid (AA) was studied in segments, microdissected from the rat kidney, which are sensitive to arginine vasopressin (AVP). In the presence of 5 microM indomethacin, the addition of 5 microM AA did not impair AVP-dependent cAMP accumulation (measured during 4 min at 35 degrees C) in the cortical or outer medullary collecting tubule, but decreased this response in the thick ascending limb with an inhibition much more pronounced in the medullary portion (MTAL) than in the cortical portion. In MTAL, the response to 10 nM AVP was inhibited by 34.4 +/- 9.6% (SEM) and 65.8 +/- 5.4% with 1 microM and 5 microM AA, respectively, N = 5 experiments. AVP-, glucagon- and calcitonin-sensitive cAMP levels in MTAL were inhibited by 5 microM AA to a similar extent. AA-induced inhibition was unaffected by the presence of inhibitors of AA metabolism: (1) either 10 microM indomethacin or 50 microM ibuprofen added to all media; (2) a 10-min pre-incubation and a 4-min incubation of MTAL samples with 10 microM eicosa-5,8,11,14-tetrayonic acid, (3) a 1-h preincubation with either 30 microM SKF-525A, 20 microM ketoconazole, or 20 microM nordihydroguariaretic acid. In contrast to AA, 11 other saturated or unsaturated fatty acids had no inhibitory effect on the AVP-dependent cAMP level. In fura-2-loaded MTAL samples, AA induced a slow increase of the intracellular calcium concentration ([Ca2+]i) which reached 21.0 +/- 3.8 nM and 92.9 +/- 21.4 nM over basal values (n = 11) at 2 min and 4 min, respectively, after the beginning of the superfusion of 5 microM AA. AA-induced inhibition of AVP-dependent cAMP accumulation was due neither to the increase in [Ca2+]i elicited by AA, nor to an activation of protein kinase C because this inhibition: (1) was not blocked when MTAL samples were incubated either in zero Ca2+ medium, or in the presence of 1,2-bis(2-aminophenoxy)ethane-N, N, N', N'-tetraacetic acid (BAPTA) to chelate [Ca2+]i, and (2) it was not reproduced by a pre-treatment of MTAL segments with a phorbol ester. Pre-incubation of MTAL (6 h at 35 degrees C) with 500 ng/ml pertussis toxin (PTX) prevented AA-induced inhibition: in the presence of PTX inhibition was 24.7 +/- 6.6% vs 10 nM AVP, as compared to 81.6 +/- 4.0% in control groups, i.e in the absence of PTX, N = 6.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell‐specific coupling of PGE2 to different transduction pathways in arginine vasopressin‐ and glucagon‐sensitive segments of the rat renal tubule

“…The sensitivity of sulprostone to inhibit the response to AVP is much higher in MTAL then in OMCD. The concentration of sulprostone eliciting half-maximal inhibition is similar to that previously observed with PGE 2 in the MTAL (Torikai & Kurokawa, 1983;Firsov et al, 1995) and the OMCD (ChabardeÁ s et al, 1990). These observations suggest that, in the rat nephron, sulprostone is as e ective as PGE 2 to decrease AVP-dependent cyclic AMP accumulation whatever the transduction pathway accounted for this regulation.…”

“…In AVPsensitive cells of the OMCD, the decrease of cyclic AMP content results from PGE 2 -mediated [Ca 2+ ] i increases through a process insensitive to PTX. Compared to the low sensitivity of PGE 2 in the OMCD (ChabardeÁ s et al, 1990), the high sensitivity of PGE 2 (Torikai & Kurokawa, 1983;Firsov et al, 1995) and sulprostone (this study) to inhibit hormonedependent cyclic AMP synthesis in the MTAL suggest that low concentrations of PGE 2 can be very e ective to regulate physiological functions of the rat thick ascending limb.…”

“…The experimental conditions used to measure hormonedependent cyclic AMP accumulation on an intact single segment have been detailed previously (ChabardeÁ s et al, 1990;Aarab et al, 1993;Firsov et al, 1995) and will be recalled brie¯y here. Experiments were performed on anaesthetized (pentobarbital, 6 mg 100 g 71 body weight) male Wistar rats (140 ± 180 g of body weight, I a-Credo, France).…”

“…Previous studies on rat microdissected segments have established that the AVPdependent cyclic AMP accumulation can be decreased by prostaglandin E 2 (Torikai & Kurokawa, 1983;ChabardeÁ s et al, 1990;Aarab et al, 1993;Firsov et al, 1995;De Jesus Ferreira et al, 1998). However, depending on the segment studied, the transduction pathway involved in prostaglandin E 2 (PGE 2 )-mediated regulation of AVP-dependent cyclic AMP accumulation appears di erent.…”

“…However, depending on the segment studied, the transduction pathway involved in prostaglandin E 2 (PGE 2 )-mediated regulation of AVP-dependent cyclic AMP accumulation appears di erent. In the medullary portion of the thick ascending limb (MTAL), PGE 2 inhibits cyclic AMP synthesis (Torikai & Kurokawa, 1983;Firsov et al, 1995) by a process sensitive to Bordetella pertussis toxin (PTX) and thus presumably through interactions with GTP-dependent Gai proteins. In contrast, in the outer medullary portion of the rat collecting duct (OMCD), PGE 2 -induced inhibition of AVPdependent cyclic AMP accumulation appears mediated mainly by an increase of the cyclic AMP breakdown (ChabardeÁ s et al, 1990) by a process insensitive to PTX (Aarab et al, 1993).…”