A large, multiple-conductance chloride channel in normal human T lymphocytes

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Abstract
Chloride (Cl) channels have been proposed to play roles in lymphocyte functions including volume regulation and cellular cytotoxicity; however, direct studies of such channels in normal human lymphocytes are lacking. In the present study we describe a large conductance Cl channel observed in about 50% of excised, inside-out patches from normal human peripheral T lymphocytes. The channel has multiple conductance states with linear single-channel current-versus-voltage relationships in symmetrical Cl solutions. The most prevalent state is the largest, which has a conductance of about 365 pS. The channel closes in a voltage-dependent manner at both negative and positive potentials, but does not show voltage-dependent inactivation. The probability of opening is maximal between −15 mV and +15 mV and the voltage dependence is well described by two Boltzmann equations with half-maximal probabilities at −22.8 mV and +18.0 mV. The slopes of the voltage dependence suggest two gates in series with 5.7 and 9.6 equivalent charges. The channel was about 30 times more selective for Cl− than for Na+ or K+ under balanced osmolarity but less selective (approx. 11∶1) under a large osmotic gradient. The single-channel conductance increased with Cl concentration with an apparent saturation at about 581 pS and a Michaelis-Menten constant of about 120 mM. The selectivity sequence among anions, determined from changes in reversal potential was: I− > NO 3 − > Br−, Cl− > F−, isethionate, HCO 3 − > SO 4 2− > gluconate, propionate > aspartate ≫ Na+, K+ and was apparently the same for subconductance states. The sequence determined from measurable values of single-channel conductance was: I− > NO 3 − > Br− > Cl− > F− > HCO 3 − , isethionate. The channel was rapidly and reversibly blocked by 1 mM Zn2+ or 1 mM Ni2+ added to the cytoplasmic face. Possible roles of this maxi-Cl channel in lymphocyte function are discussed.