Src Family Kinase Involvement in Angiotensin II Induced Contraction of Rat Thoracic Aorta

Ketul Patel, Phillip Aaronson
Kings College, London, United Kingdom

Angiotesin II causes vasoconstriction via a tyrosine kinase dependent mechanism. The specific tyrosine kinases involved are unclear. One candidate is the Src family of which the 60 KD c-Src is the best characterised. C-Src has been implicated in α2-adrenergic contraction of the porcine palmer lateral vein (Roberts, 2001) and angiotensin II induced contractions in mesenteric vasculature (Touyz et al., 2001) and rat renal vasculature (Che et al., 2005). However it is not involved in α2-adrenergic contraction of rat thoracic aorta (Carter et al., 2002). This study was performed to investigate the potential role of Src in angiotensin II induced contraction of rat thoracic aorta.

2.5mm thoracic aortic rings from male wister rats were suspended in a physiological buffer and challenged with 10μM phenylephrine solution. Each ring was then pre-treated with a tyrosine kinase inhibitor or inactive analogue and challenged with a 1μM angiotensin II solution. Tyrphostin A23 or the inactive analogue tyrphostin A1 was used as a global tyrosine kinase inhibitor. PP2 or the inactive analogue PP3 was used as the Src specific tyrosine kinase inhibitor. Isometric tension generated on addition of angiotensin II was expressed as a percentage of the maximum tension generated following the phenylephrine challenge. Inhibition was calculated by dividing this value with that when the vehicle only was used (control). Data was expressed as mean ± standard error and compared by Student’s paired t test. P < 0.05 denoted a significant difference.

100μM tyrphostin A23 significantly attenuated contraction (24± 3.9% (mean ± SE)) (p<0.05). Increasing the concentrations of PP2 caused a dose dependent inhibition of angiotensin II induced contraction. 6μM PP2 significantly attenuated contraction (25 ± 11%) (p<0.05). 30μM, PP2 inhibited contraction by 60 ± 6.4% (p<0.05). The inactive analogues did not alter the contractile response

The fact that tyrphostin A23 significantly attenuated contraction, confirms that tyrosine kinases are required for angiotensin II induced contraction of rat aorta. At a concentrations of 6μM, PP2 also attenuated angiotensin II induced vasoconstriction. PP2 is known to be selective at low micromolar concentrations in intact cells (Hanke et al., 1996). 30μM PP3 was without effect. In conclusion our study demonstrates for the first time that Src activity is necessary for angiotensin II induced contraction of rat aorta. Previous studies have shown that the involvement of the Src family of kinases in the contractile response is variable. Our results are in support of the theory that the specific tyrosine kinases that participate in vasoconstriction differ between species, vessels and agonists.

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