Cl- channels in intact human T lymphocytes.

Area of Science:

• Ion channel physiology
• Cellular electrophysiology
• Lymphocyte biology

Background:

• Previously, a large, multiple-conductance chloride channel (Cl-) was identified in excised T lymphocyte patches, resembling maxi-Cl- channels.
• This channel's voltage dependence in excised patches limited its opening to nonphysiological voltages, with rare activity observed in cell-attached patches.

Purpose of the Study:

• To investigate the activation of Cl- channels in intact T lymphocytes at physiological temperatures and voltages.
• To determine if channel properties change upon patch excision.

Main Methods:

• Utilized cell-attached and inside-out patch-clamp recordings from normal T lymphocytes.
• Manipulated temperature (above 32°C vs. room temperature) and voltage to assess channel activity.
• Investigated the role of intracellular calcium (Ca2+) using ionomycin and mitogens.
• Examined the effects of specific blockers: zinc (Zn2+), SITS, DIDS, and NPPB.

Main Results:

• Maxi-Cl- channels were reversibly activated in 69% of cell-attached patches above 32°C, contrasting with <2% at room temperature.
• Upon excision, these channels exhibited characteristics similar to previously reported excised patches and were active at room temperature.
• Channel voltage dependence differed significantly between cell-attached and excised patches, with opening possible at physiological resting potentials in intact cells.
• Channel activation was independent of intracellular Ca2+ fluctuations.
• Single-channel currents were blocked by Zn2+, SITS, DIDS, and NPPB.

Conclusions:

• T lymphocyte Cl- channels can be activated in intact cells under physiological conditions (temperature and voltage).
• Patch excision alters channel properties, enabling activity at room temperature and different voltage dependencies.
• These maxi-Cl- channels are not Ca2+-dependent and can be modulated by specific chemical blockers.