Extracellular Mg2+- and Ca2+-sensing in mouse distal convoluted tubule cells

An immortalized cell line (designated MDCT) has been extensively used to investigate the cellular mechanisms of electrolyte transport within the mouse distal convoluted tubule. Mouse distal convoluted tubule cells possess many of the functional characteristics of the in vivo distal convoluted tubule. In the present study, we show that MDCT cells also possess a polyvalent cation-sensing mechanism that is responsive to extracellular magnesium and calcium. Southern hybridization of reverse transcribed-polymerase chain reaction (RT-PCR) products, sequence determination and Western analysis indicated that the calcium-sensing receptor (Casr) is expressed in MDCT cells. Using microfluorescence of single MDCT cells to determine cytosolic Ca2+ signaling, it was shown that the polyvalent cation-sensing mechanism is sensitive to extracellular magnesium concentration ([Mg2+](o)) and extracellular calcium concentration ([Ca2+](o)) in concentration ranges normally observed in the plasma. Moreover, both [Mg2+](o) and [Ca2+](o) were effective in generating intracellular Ca2+ transients in the presence of large concentrations of [Ca2+](o) and [Mg2+](o), respectively. These responses are unlike those observed for the Cast in the parathyroid gland. Finally, activation of the polycation-sensitive mechanism with either [Mg2+](o) or [Ca2+](o) inhibited parathyroid hormone-, calcitonin-, glucagon-and arginine vasopressin-stimulated cAMP release in MDCT cells. These studies indicate that immortalized MDCT cells possess a polyvalent cation-sensing mechanism and emphasize the important role this mechanism plays in modulating intracellular signals in response to changes in [Mg2+](o) as well as in [Ca2+](o).