The vascular Ca2+-sensing receptor regulates blood vessel tone and blood pressure.

The extracellular calcium-sensing receptor CaSR is expressed in blood vessels where its role is not completely understood. In this study, we tested the hypothesis that the CaSR expressed in vascular smooth muscle cells (VSMC) is directly involved in regulation of blood pressure and blood vessel tone. Mice with targeted CaSR gene ablation from vascular smooth muscle cells (VSMC) were generated by breeding exon 7 LoxP-CaSR mice with animals in which Cre recombinase is driven by a SM22α promoter (SM22α-Cre). Wire myography performed on Cre-negative [wild-type (WT)] and Cre-positive (SM22α)CaSR(Δflox/Δflox) [knockout (KO)] mice showed an endothelium-independent reduction in aorta and mesenteric artery contractility of KO compared with WT mice in response to KCl and to phenylephrine. Increasing extracellular calcium ion (Ca(2+)) concentrations (1-5 mM) evoked contraction in WT but only relaxation in KO aortas. Accordingly, diastolic and mean arterial blood pressures of KO animals were significantly reduced compared with WT, as measured by both tail cuff and radiotelemetry. This hypotension was mostly pronounced during the animals' active phase and was not rescued by either nitric oxide-synthase inhibition with nitro-l-arginine methyl ester or by a high-salt-supplemented diet. KO animals also exhibited cardiac remodeling, bradycardia, and reduced spontaneous activity in isolated hearts and cardiomyocyte-like cells. Our findings demonstrate a role for CaSR in the cardiovascular system and suggest that physiologically relevant changes in extracellular Ca(2+) concentrations could contribute to setting blood vessel tone levels and heart rate by directly acting on the cardiovascular CaSR.

Molecular and clinical analysis of a neonatal severe hyperparathyroidism case caused by a stop mutation in the calcium-sensing receptor extracellular domain representing in effect a human 'knockout'.

OBJECTIVE: Loss-of-function calcium-sensing receptor (CAR) mutations cause elevated parathyroid hormone (PTH) secretion and hypercalcaemia. Although full Car deletion is possible in mice, most human CAR mutations result from a single amino acid substitution that maintains partial function. However, here, we report a case of neonatal severe hyperparathyroidism (NSHPT) in which the truncated CaR lacks any transmembrane domain (CaR(R392X)), in effect a full CAR 'knockout'. CASE REPORT: The infant (daughter of distant cousins) presented with hypercalcaemia (5.5-6  mmol/l corrected calcium (2.15-2.65)) and elevated PTH concentrations (650-950  pmol/l (12-81)) together with skeletal demineralisation. NSHPT was confirmed by CAR gene sequencing (homozygous c.1174C-to-T mutation) requiring total parathyroidectomy during which only two glands were located and removed, resulting in normalisation of her serum PTH/calcium levels. DESIGN AND METHODS: The R392X stop codon was inserted into human CAR and the resulting mutant (CaR(R392X)) expressed transiently in HEK-293 cells. RESULTS: CaR(R392X) expressed as a 54  kDa dimeric glycoprotein that was undetectable in conditioned medium or in the patient's urine. The membrane localisation observed for wild-type CaR in parathyroid gland and transfected HEK-293 cells was absent from the proband's parathyroid gland and from CaR(R392X)-transfected cells. Expression of the mutant was localised to endoplasmic reticulum consistent with its lack of functional activity. CONCLUSIONS: Intriguingly, the patient remained normocalcaemic throughout childhood (2.5 mM corrected calcium, 11 pg/ml PTH (10-71), age 8 years) but exhibited mild asymptomatic hypocalcaemia at age 10 years, now treated with 1-hydroxycholecalciferol and Ca2+ supplementation. Despite representing a virtual CAR knockout, the patient displays no obvious pathologies beyond her calcium homeostatic dysfunction.

Sustained nitric oxide production via l-arginine administration ameliorates effects of intestinal ischemia-reperfusion.

BACKGROUND: The role of nitric oxide in intestinal ischemia-reperfusion is unclear-some studies link it to the harmful effects of ischemia-reperfusion, while others report it to be protective. We propose that nitric oxide levels diminish in the reperfusion period in conjunction with the onset of increased capillary permeability. The aim of this study is to determine the effect of supplementing nitric oxide synthase with its substrate, l-arginine, on development of local mucosal injury and systemic capillary leak. MATERIALS AND METHODS: Rats underwent 30 min of superior mesenteric artery occlusion followed by 4 h of reperfusion. The vehicle groups received l-arginine either intravenously (4 mg/kg/min) or into the intestinal lumen. The intravenous groups received l-arginine either before the ischemic event or after 30 min of reperfusion. Capillary leak in the gut and lung were measured, as were degree of mucosal injury and number of infiltrating neutrophils. Appropriate controls were performed. RESULTS: Thirty minutes of mesenteric ischemia followed by 4 h of reperfusion significantly increased gut and lung leak, neutrophil infiltration, and the severity of mucosal injury. l-Arginine given iv prior to ischemia inhibited lung leak, mucosal injury, and neutrophil infiltration. When arginine was given during the reperfusion period, lung leak and neutrophil infiltration but not mucosal injury were reduced. Intraluminal l-arginine reduced mucosa injury, but had no effect on capillary leak. CONCLUSIONS: Supplementation with l-arginine enhances NO production, resulting in reduced systemic endothelial dysfunction. This may act as a useful clinical adjunct in the management of trauma patients in preventing the development of ARDS and multiple organ failure.