The calcium-sensing receptor (CaR) stimulates ERK1 in rat fibroblasts, but its effect on other MAP kinases is not known. We used a model of renal distal tubule, the MDCK cell, to determine the effects of Call. stimulation on Jun kinase (JNK) activity. Stimulation of the Call with 5 mM Ca2+ resulted in a time-dependent increase in JNK activity. Activation of JNK occurred preferentially with stimulation on the basal surface relative to the apical surface. Basal administration of the CaR agonist gadolinium (30 mu m) also stimulated JNK activity. Pertussis toxin blocked the ability of both CaR agonists to stimulate JNK, indicating that the effect was mediated through G(i alpha) class G proteins. Finally, we used confocal microscopy to determine that the CaR was located predominantly on the basal surface. These studies demonstrate for the first time that the CaR stimulates JNK activity.