Ca2+-sensing receptor-mediated regulation of volume-sensitive Cl- channelsin human epithelial cells

1. 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 volum e-sensitive Cl- channels in a human epithelial cell line (Intestine 407). 2. Reverse transcriptase-polymerase chain reaction and immunoblotting analy sis showed that Intestine 407 cells express CaR mRNA and protein. 3. 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. 4. Neomycin, spermine and La3+ augmented volume-sensitive Cl- currents. How ever, these CaR agonists failed to affect depolarization-induced inactivati on. 5. Intracellular application of GTP gammaS, but not GDP betaS, increased th e 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 GTP gammaS or GDP betaS. In contrast, GTP gammaS and GD P betaS failed to affect the inactivation kinetics of the Cl- current and t he accelerating effect of Ca2+ thereon. 6. The Cl- current amplitude was enlarged by stimulation with forskolin, di butyryl cAMP and IBMX. During the cAMP stimulation, extracellular Ca2+ fail ed to increase the Cl- current but did accelerate depolarization-induced in activation. 7. It is concluded that stimulation of the CaR induces upregulation of volu me-sensitive Cl- channels via a G: protein-mediated increase in intracellul ar cAMP in the human epithelial cell. However, the accelerating effect of e xtracellular divalent cations on the inactivation kinetics of the Cl- curre nt is induced by a mechanism independent of the CaR and cAMP.