Proceedings of The Physiological Society

Physiology 2014 (London, UK) (2014) Proc Physiol Soc 31, PCB189

Poster Communications

Contractile desensitisation to UTP is enhanced in spontaneously-hypertensive rats only after hypertension is established

C. A. Nash2, R. Jackson1, R. Challiss2, J. M. Willets3, R. D. Rainbow1

1. Cardiovascular Sciences, University of Leicester, Leicester, United Kingdom. 2. Cell Physiology and pharmacology, University of Leicester, Leicester, United Kingdom. 3. Cancer Studies & Molecular Medicine, University of Leicester, Leicester, United Kingdom.

Spontaneously-hypertensive rats (SHR) develop hypertension between 6 and 10 weeks of age. The mechanisms of development of hypertension are not clear, however it has been suggested that there are both increases in calcium channel subunit expression and alterations in GPCR signalling. We hypothesised that contractile desensitisation would be attenuated in SHR compared to Wistar Kyoto (WKY) or Wistar rats, therefore increasing the contractile response and so contributing to the hypertensive phenotype. Briefly, male SHR, WKY or Wistar rats were culled and mesenteric arteries removed for use on a wire-myograph. 3rd order vessels were mounted from 6 week old SHR and WKY, or 12 week old SHR, WKY and Wistar animals and held at a tension equivalent to a pressure of 90 mmHg. Contractile responses to angiotensin II, endothelin-1 and UTP were equivalent in SHR, WKY and Wistar animals at both 6 and 12 weeks of age. Contraction in response to depolarisation with 60 mM K+ was enhanced in SHR at both 6 (25±2.3 vs 12±1.3 mN/mm, P<0.001) and 12 weeks (20.8±4.5 vs 8.6±1.8 mN/mm, P<0.001) compared to WKY. Contractile desensitisation was assessed using a 5 min pulse of an EC50 concentration of UTP, 5 min washout, a desensitising maximal UTP concentration for 5 min, wash and a re-application of an EC50 concentration of UTP for 5 min (1). Desensitisation was assessed by expressing the second EC50 response as a percentage of the first, a larger percentage representing a greater desensitisation. In vessels from 6 week-old animals, there was no difference in the contractile desensitisation between SHR and WKY (32±5 % vs 31±4 %, P>0.05). However, at 12 weeks of age there was a significant increase in contractile desensitisation (WKY 33±9 % vs SHR 65±5 %). Wistar age-matched animals showed a similar level of desensitisation to WKY animals (36±4 %). All data from ≥8 vessels from ≥4 animals and were compared using a Student's t-test (SHR and WKY) or one-way ANOVA (with Bonferroni's post-hoc test) for comparison of all 3 rat strains.G protein-coupled receptor kinase-2 (GRK2) is thought to be a key regulator of GPCR desensitisation. Using western blotting, the GRK2 expression was probed in WKY and SHR mesenteric smooth muscle. Expression of GRK2 was markedly increased by 1.7 fold in SHR compared to WKY at 12 weeks of age (p<0.05), however no difference was observed in 6 week-old rats.These data demonstrate that the expression of GRK2 and the desensitisation of contractile response are increased in SHR compared to WKY and Wistar rats. These data suggest that, rather than contributing to the hypertensive phenotype, the increased desensitisation response may actually be a compensatory development to oppose the enhanced contractile phenotype in the hypertensive animals.

Where applicable, experiments conform with Society ethical requirements