Possible role of TRP channels in the EDHF response of mesenteric arteries from streptozotocin-induced diabetic rats

Mais Absi1, Hani Oso1, Hussam Gareeb1, Ahmad Khalil1, Marwan Khattab1, Urs Ruegg2. 1Aleppo University, Aleppo, Syria, 2Geneva University, Geneva, Switzerland

Introduction: Diabetes is associated with vascular complications in which endothelial dysfunction plays an important role. The endothelium-derived hyperpolarizing factor EDHF response, which involves the opening of endothelial small- (SKCa)- and intermediate-conductance (IKCa) calcium-activated potassium channels, is a critical contributor to the regulation of vascular function. In addition, transient receptor potential vanilloid (TRPV) calcium channels also have an important role in the regulation of blood pressure and vascular resistance. In the present study, the possible contributions of TRPV channels to the EDHF response were investigated in mesenteric arteries of rats with STZ-induced diabetes.

Methods: Male albino Wistar rats (220-300g) were used. Diabetes was induced by a single intravenous injection of STZ (60 mg/kg of body weight) into the tail vein. At the time of experiments the tail blood glucose level was above 350 mg/dl. Mesenteric arteries (second order branch; 300–350μm) were pressurized to 70 mm Hg and pre-contracted with phenylephrine. ACh- or NS309- (direct opener of IKCa and SKCa channels) mediated responses were measured in the presence of the NO synthase inhibitor N-nitro-L-arginine methyl ester (300 µM) and cyclooxygenase inhibitor indomethacin (10 µM).

Results: In control arteries, the relaxation to 1µM ACh (84.8 ± 2.8%; n = 8) in control vessels was significantly decreased in comparison with diabetics (22.5 ± 5.8%; n = 10). The ACh response was depressed by 1 μM ruthenium red (RuR, a blocker of TRPV channels; 50.6 ± 8.7% control vs. 15.7 ± 3.3% diabetics, n = 6). This indicates that TRPV may contribute to agonist-induced Ca2+ signaling and EDHF-dependent vasodilatation, a response which is reduced by diabetes. Both SKCa and IKCa-mediated EDHF responses were also significantly reduced by diabetes (in the presence of 1 µM TRAM-34, a blocker of IKCa, 55.5 ± 3.7 % control vs 10.8 ± 3.5% diabetic; n≥5; in the presence of 100 nM apamin, a blocker of SKCa, 31.1 ± 3.3% control vs 9.5 ± 2.5% diabetic n≥5). However, the impaired vasodilatation mediated by SKCa or IKCa was unaffected by RuR (in the presence of TRAM-34, 50.7 ± 11.3% control vs 12.5 ± 2.3 % diabetics; in the presence of apamin 30.0 ± 9.0% control vs 10.6 ± 2.7% diabetics; n≥4). NS309 (1uM) relaxations were also significantly reduced in diabetic arteries and by treatment with RuR (78.5 ± 8.7% control vs 32.1 ± 5.8% diabetics; and in presence of RuR: 39.9 ± 9.5% control vs 19.8 ± 3.6% diabetics; n≥5). NS309-mediated vasorelaxations mediated by direct opening of SKCa and IKCa were also significantly affected by diabetes (in the presence of TRAM-34: 27.0± 4.40% control vs 14.80± 2.70% diabetics; with apamin: 52.6 ± 8.9% control vs 25.4 ± 5.7% diabetics; n≥5). RuR reduced the dilation mediated by SKCa and IKCa in both control and diabetic arteries (in presence of TRAM-34: 13.9 ± 4.0% control vs 8.2 ± 0.7% diabetics and in the presence of apamin: 16.6 ± 1.03% control vs 8.9 ± 0.3% diabetics; n≥4).

Conclusions: These data show that EDHF induces activation of IKCa and SKCa channels via TRPV channels leading to vasodilatation of mesenteric arteries and that these responses are impaired in diabetic rats. This suggests that KCa and TRPV channels are potential therapeutic targets to improve endothelial function in diabetes.