Proceedings of The Physiological Society

Physiology 2015 (Cardiff, UK) (2015) Proc Physiol Soc 34, C36

Oral Communications

The calcium-sensing receptor in vascular smooth muscle and endothelial cells elicits opposing effects on vascular tone

M. Schepelmann1,2, P. Yarova1, I. Lopez-Fernandez1,3, S. C. Brennan1, T. Davies1, A. Aggarwal4, A. Herberger5, J. Hwong5, W. Chang5, V. Matchkov6, D. Ward7, R. Mentaverri3, D. Edwards8, P. J. Kemp1, D. Riccardi1

1. School of Biosciences, Cardiff University, Cardiff, United Kingdom. 2. School of Pharmacy and Pharmaceutical Sciences, Cardiff University, Cardiff, United Kingdom. 3. Faculty of Pharmacy, Université de Picardie Jules Verne, Amiens, France. 4. Department of Pathophysiology and Allergy Research, Medical University of Vienna, Vienna, Austria. 5. Endocrine Research Unit, University of California San Francisco, San Francisco, California, United States. 6. Department of Biomedicine, Aarhus University, Aarhus, Denmark. 7. Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom. 8. School of Medicine, Cardiff University, Cardiff, United Kingdom.

Background: The extracellular calcium-sensing receptor (CaSR) is expressed in vascular smooth muscle cells (VSMC) and endothelial cells (EC) of blood vessels where its functions are not well defined. To elucidate the role of the CaSR in the VSMC, we generated mice with constitutive targeted CaSR gene ablation by crossing exon 7 LoxP-CaSR and SM22α-Cre mice. Methods and results: All results shown as mean±SEM. Ex vivo wire myography performed on aortae and mesenteric arteries of Cre-negative (wild-type, WT) and SM22αCaSR∆flox/∆flox (VSMC-knock-out, VSMC-KO) showed that and phenylephrine (PE)-induced contractility was significantly reduced in blood vessels from VSMC-KO animals compared to WT (e.g. at 1 µM PE, aorta: N=18 KO and 19 WT, 78.9±6.3% vs 51.6±5.1% of max WT response, p<0.001 extra sum-of-squares F-test for comparison of fitted curves (ESSqF) which was not abolished by endothelial denudation or inhibition of NO synthase by NG-nitro-L-arginine methyl ester (L-NAME). Furthermore, exposing the vessels increasing extracellular calcium concentrations [Ca2+]o evoked contraction followed by relaxation in WT, but only relaxation in KO aortae (e.g. at 3 mM Ca2+, N=9, 19.9±7.8% contraction vs. 24.7±9.7% relaxation compared to baseline, p<0.001, ESSqF). These results suggest an endothelium-independent role for the VSMC-CaSR in contributing to blood vessel contractility. In vitro, Ca2+o or KCl elicited reduced intracellular Ca2+ responses in isolated VSMC from KO animals compared to WT. As expected, CaSR deletion from VSMC had an effect on blood pressure in vivo, where we observed hypotension in VSMC-KO compared to WT using tail cuff and radiotelemetry which was greatest during the night when the animals were active (N=5, 112.1±2.6 vs. 127.3 4.9 mm Hg systolic p<0.05 and 81.3±2.2 vs 101.4±4.9 mm Hg diastolic p<0.01, Holm-Sidak post-test of two-way ANOVA, surgery under general anesthesia using s.c. fluanisone 10 mg/kg body-weight, fentanyl 0.3 mg/kg and midazolam 1 mg/kg). To compare the effects of the VSMC-CaSR to those of the EC-CaSR, we assessed the vascular contractility of EC-CaSR knock out mice by crossing exon 7 LoxP-CaSR mice and inducible platelet derived growth factor subunit B (iPDGFB)-Cre mice (5 days tamoxifen injection). In contrast to the VSMC-KO mice, aortic contractility in response to PE of these iPDGFBCaSRΔflox/Δflox mice was significantly enhanced compared to WT (e.g. at 1 µM PE, N=9 KO and N=6 WT, 108.2±20.6 vs. 68.7±11.5, p<0.001, ESSqF) which was totally abolished by L-NAME, suggesting a NO-mediated vasodilatory effect of the EC-CaSR. Conclusions: Our findings clearly demonstrate that the vascular CaSR contributes to modulation of vascular tone and blood pressure, with opposing effects depending on the vascular cell type: the VSMC-CaSR contributes to arterial contraction while the EC-CaSR mediates arterial dilation.

Where applicable, experiments conform with Society ethical requirements