CHLORIDE CHANNELS ACTIVATED BY OSMOTIC-STRESS IN T-LYMPHOCYTES

We have used whole-cell and perforated-patch recording techniques to c haracterize volume-sensitive Cl- channels in T and B lymphocytes. Posi tive transmembrane osmotic pressure (intracellular osmolality > extrac ellular osmolality) triggers the slow induction of a Cl- conductance. Membrane stretch caused by cellular swelling may underlie the activati on mechanism, as moderate suction applied to the pipette interior can reversibly oppose the induction of Cl- current by an osmotic stimulus. Intracellular ATP is required for sustaining the Cl- current. With AT P-free internal solutions, the inducibility of Cl- current declines wi thin minutes of whole-cell recording, while in.whole-cell recordings w ith ATP or in perforated-patch experiments, the current can be activat ed for at least 30 min. The channels are anion selective with a permea bility sequence of I- > SCN- > NO3-, Br- > Cl- > MeSO3- > acetate, pro pionate > ascorbate > aspartate and gluconate. G(Cl) does not show vol tage- and time-dependent gating behavior at potentials between - 100 a nd + 100 mV, but exhibits moderate outward rectification in symmetrica l Cl- solutions. Fluctuation analysis indicates a unitary chord conduc tance of approximately 2 pS at - 80 mV in the presence of symmetrical 160 mM Cl-. The relationship of mean current to current variance durin g the osmotic activation of Cl- current implies that each cell contain s on the order of 10(4) activatable Cl- channels, making it the most a bundant ion channel in lymphocytes yet described. The current is block ed in a voltage-dependent manner by DIDS and SITS (K(i) = 17 and 89 mu M, respectively, at + 40 mV), the degree of blockade increasing with m embrane depolarization. The biophysical and pharmacological properties of this Cl- channel are consistent with a role in triggering volume r egulation in lymphocytes exposed to hyposmotic conditions.