Volume-regulated chloride conductance in the LNCaP human prostate cancer cell line

Patch-clamp recordings were used to study ion currents induced by cell swelling caused by hypotonicity in human prostate cancer epithelial cells, LNCaP. The reversal potential of the swelling-evoked current suggested that Cl- was the primary charge carrier (termed I-Cl,I-swell). The selectivity sequence of the underlying volume-regulated anion channels (VRACs) for different anions was Br- approximate to I- > Cl- > F- > methanesulfonate >> glutamate, with relative permeability numbers of 1.26, 1.20, 1.0, 0.77, 0.49, and 0.036, respectively. The current-voltage patterns of the whole cell currents as well as single-channel currents showed moderate outward rectification. Unitary VRAC conductance was determined at 9.6 +/- 1.8 pS. Conventional Cl- channel blockers 5-nitro-2-(3-phenylpropylamino) benzoic acid (100 mu M) and DIDS (100 mu M) inhibited whole cell I-Cl,I-swell in a voltage-dependent manner, with the block decreasing from 39.6 +/- 9.7% and 71.0 +/- 11.0% at +50 mV to 26.2 +/- 7.2% and 14.5 +/- 6.6% at -100 mV, respectively. Verapamil (50 mu M), a standard Ca2+ antagonist and P-glycoprotein function inhibitor, depressed the current by a maximum of 15%. Protein tyrosine kinase inhibitors downregulated ICl, swell (genistein with an IC50 of 2.6 mu M and lavendustin A by 60 +/- 14% at 1 mM). The protein tyrosine phosphatase inhibitor sodium orthovanadate (500 mu M) stimulated I-Cl,I-swell by 54 +/- 11%. We conclude that VRACs in human prostate cancer epithelial cells are modulated via protein tyrosine phosphorylation.