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

Bapty BW, Dai LJ, Ritchie G, Jirik F, Canaff L, Hendy GN, and Quamme GA: Extracellular  Mg2+-and Ca2+-sensing in mouse distal convoluted tubule cells. Kidney International 53:583-592,     1998.

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Abstract 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 Ca21 signaling, it was shown that the polyvalent cation-sensing mechanism is sensitive to extracellular magnesium concentration ([Mg21]o) and extracellular calcium concentration ([Ca21]o) in concentration ranges normally observed in the plasma. Moreover, both [Mg21]o and [Ca21]o were effective in generating intracellular Ca21 transients in the presence of large concentrations of [Ca21]o and [Mg21]o, respectively. These responses are unlike those observed for the Casr in the parathyroid gland. Finally, activation of the polycationsensitive mechanism with either [Mg21]o or [Ca21]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 [Mg21]o as well as in [Ca21]o.

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 Ca21 signaling, it was shown
that the polyvalent cation-sensing mechanism is sensitive to extracellular
magnesium concentration ([Mg21]o) and extracellular calcium concentration
([Ca21]o) in concentration ranges normally observed in the plasma.
Moreover, both [Mg21]o and [Ca21]o were effective in generating intracellular
Ca21 transients in the presence of large concentrations of [Ca21]o
and [Mg21]o, respectively. These responses are unlike those observed for
the Casr in the parathyroid gland. Finally, activation of the polycationsensitive
mechanism with either [Mg21]o or [Ca21]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 [Mg21]o as well as in [Ca21]o.

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