Sensitivity of Ca-sensing receptor-transient receptor potential-mediated Ca influx to extracellular acidity in bEND.3 endothelial cells.

Ca-sensing receptors (CaSRs) are G protein-coupled receptors activated by elevated concentrations of extracellular Ca. In our previous works, we showed protein and functional expression of CaSR in mouse cerebral endothelial cell (EC) (bEND.3); the CaSR response (high Ca-elicited cytosolic [Ca] elevation) was unaffected by suppression of phospholipase C but in part involved Ca influx through transient receptor potential V1 (TRPV1) channels. In this work, we investigated if extracellular acidity affected CaSR-mediated Ca influx triggered by high (3 mM) Ca (CaSR agonist), 3 mM spermine (CaSR agonist), and 10 mM cinacalcet (positive allosteric modulator of CaSR). Extracellular acidosis (pH 6.8 and pH 6.0) strongly suppressed cytosolic [Ca] elevation triggered by high Ca, spermine, and cinacalcet; acidosis also inhibited Mn influx stimulated by high Ca and cinacalcet. Purinoceptor-triggered Ca response, however, was not suppressed by acidosis. Extracellular acidity also did not affect membrane potential, suggesting suppressed CaSR-mediated Ca influx in acidity did not result from the reduced electrical driving force for Ca. Our results suggest Ca influx through a putative CaSR-TRP complex in bEND.3 EC was sensitive to extracellular pH.