Resting tension is important for the contractile response but not to vasodilatation in renal hypertensive rat aorta

Abstract

Nitric oxide (NO) produced by the NO‐Synthase (NOS) controls vascular tone and systemic arterial pressure. Shear stress‐mediated phosphorylation of NOS regulates NOS activity. Phosphorylation of Ser1177 (P‐Ser) activates NOS and Thr495 (P‐Thr) inactivates NOS. Protein kinase Akt/PI3K and c‐Src are enzymes that can phosphorylate these residues, but the signaling in renal hypertensive (2K‐1C) rat aorta submitted to increasing resting tension is not known. This study aimed to evaluate the effects of the resting tension of 1.5 g (control) and 3.0 g on the eNOS phosphorylation in phenylephrine (PE)‐induced contractile response in isolated 2K‐1C rat aorta. Concentration‐effect curves for PE were constructed in aortas under resting tension of 1.5 g and 3.0 g in the absence or presence of NOS inhibitor (L‐NAME, 100 μM). On the top of maintained contraction to PE, concentration‐effect curves for acetylcholine (ACh) were constructed. The expression of P‐Ser and P‐Thr were evaluated by Western Blot. The maximum effect induced by PE on resting tension of 1.5 g was lower in 2K‐1C (1.2 ± 0.2g, n=7; p<0.001) than in normotensive 2K (2.2 ± 0.1g; n=5). This effect was normalized by NOS inhibition with L‐NAME. Both P‐Ser and P‐Thr expressions were higher in 2K‐1C than in 2K aortas. In 2K‐1C the increased P‐Ser was inhibited by PI3K/Akt inhibitor (wortmannin, 20 μM) and the increased P‐Thr was inhibited by c‐Src inhibitor (PP1, 10 μM). Under resting tension of 3.0 g, PE‐induced contractile response was similar in 2K‐1C and 2K aortas. Increased resting tension from 1.5 g to 3.0 decreased P‐Ser and increased P‐Thr in 2K aorta, but it was not modified in 2K‐1C aorta. ACh‐induced relaxation was lower in 2K‐1C (81.4 ± 4.7%; n=7; p<0.001) than in 2K (100.5 ± 2.4%; n=5), that was not modified under 3.0 g resting tension in 2K and 2K‐1C. Taken together, our results demonstrate that the increasing resting tension from 1.5 g to 3.0 g decreases eNOS phosporylation in the activation site (P‐Ser) in 2K rat aorta. The anti‐contractile effect induced by PE in 2K‐1C rat aorta under 1.5 g tension is due to eNOS activation in a PI3K/Akt dependent way. The anti‐contractile effect is abolished by increasing the resting tension to 3.0 g due to P‐Thr in a c‐Src dependent way. These results indicate that resting tension is important for the contractile response, but not to vasodilatation in renal hypertensive (2K‐1C) rat aorta.Support or Funding InformationSupported by FAPESP, CNPq and CAPES.