Relationship between Extra- and Intracellular Calcium in Distal Segments of the Renal Tubule. Role of the Ca2+ Receptor RaKCaR

The effect of extracellular calcium ([Ca2+] e ) on cytosolic calcium ([Ca2+] i ) was investigated in thick ascending limbs and collecting ducts from the rat kidney, using the fluorescent dye fura-2. In cortical collecting ducts, basolateral but not apical changes in [Ca2+] e were associated with parallel changes in [Ca2+] i . Basal [Ca2+] i was hardly modified by nifedipine and verapamil but was decreased by 60% by basolateral La3+. Increasing peritubular [Ca2+] e triggered Ca2+ release from intracellular stores. This effect was not reproduced by agonists of the renal Ca2+-receptor RaKCaR, e.g., Ba2+, Mg2+, Gd3+, and neomycin, but was reproduced by Ni2+. Ni2+-induced mobilization of intracellular Ca2+ was larger in the inner medullary collecting duct, a segment which poorly responds to increasing [Ca2+] e .