title: Ca2+-sensing receptor-mediated regulation of volume-sensitive Cl- channels in human epithelial cells.
abstract: Since extracellular Ca2+ or Mg2+ has been reported to modulate swelling-activated Cl- currents, we examined the expression of the G protein-coupled Ca2+-sensing receptor (CaR) and its involvement in the regulation of volume-sensitive Cl- channels in a human epithelial cell line (Intestine 407). Reverse transcriptase-polymerase chain reaction and immunoblotting analysis showed that Intestine 407 cells express CaR mRNA and protein. The swelling-activated whole-cell Cl- current was voltage-independently augmented by extracellular Ca2+ or Mg2+. In addition, Ca2+ or Mg2+ voltage-dependently accelerated the inactivation kinetics of the Cl- current. Neomycin, spermine and La3+ augmented volume-sensitive Cl- currents. However, these CaR agonists failed to affect depolarization-induced inactivation. Intracellular application of GTPgammaS, but not GDPbeta]S, increased the amplitude of the swelling-induced Cl- current without affecting the basal current. The upregulating effect of Ca2+ on the Cl- current amplitude was abolished by either GTPgammaS or GDPbetaS. In contrast, GTPgammaS and GDPbetaS failed to affect the inactivation kinetics of the Cl- current and the accelerating effect of Ca2+ thereon. The Cl- current amplitude was enlarged by stimulation with forskolin, dibutyryl cAMP and IBMX. During the cAMP stimulation, extracellular Ca2+ failed to increase the Cl- current but did accelerate depolarization-induced inactivation. It is concluded that stimulation of the CaR induces upregulation of volume-sensitive Cl- channels via a G protein-mediated increase in intracellular cAMP in the human epithelial cell. However, the accelerating effect of extracellular divalent cations on the inactivation kinetics of the Cl- current is induced by a mechanism independent of the CaR and cAMP.
authors.affiliation: Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Shimizu
authors.forename: S
authors.initials: S
authors.lastname: Morishima
authors.forename: Y
authors.initials: Y
authors.lastname: Okada
mesh_terms: D001483:Base Sequence / Q000235:genetics; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D002460:Cell Line; D018118:Chloride Channels / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D004553:Electric Conductivity; D004847:Epithelial Cells / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D015870:Gene Expression; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives; D006801:Humans; D015151:Immunoblotting; D007425:Intracellular Membranes / Q000502:physiology; D008274:Magnesium / Q000378:metabolism; D008969:Molecular Sequence Data; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface / Q000819:agonists / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015290:Second Messenger Systems / Q000502:physiology
chemical_list: D018118:Chloride Channels; D044169:Receptors, Calcium-Sensing; D011956:Receptors, Cell Surface; D006160:Guanosine Triphosphate; D008274:Magnesium; D002118:Calcium