K channels are expressed early in human T-cell development.

Area of Science:

• Immunology
• Cellular Physiology

Background:

• Mature T lymphocytes require functioning potassium (K+) channels for proliferation induced by phytohemagglutinin (PHA).
• Immature thymocytes, lacking the T3 receptor, do not proliferate in response to PHA.
• The role of K+ channels in the immunoincompetence of immature T cells is unknown.

Purpose of the Study:

• To investigate whether immature T3- thymocytes lack normal K+ channels.
• To compare the characteristics and PHA responsiveness of K+ currents in immature and mature T cells.

Main Methods:

• Electrophysiological recordings of K+ currents in T3- thymocytes and mature peripheral T cells.
• Analysis of K+ channel properties including voltage dependence, kinetics, and pharmacology.
• Assessment of the functional response of K+ currents to PHA stimulation.

Main Results:

• T3- thymocytes possess K+ currents with properties (voltage dependence, kinetics, pharmacology) similar to mature T cells.
• The maximal specific K+ conductance is comparable between immature and mature T cells, indicating similar channel density.
• PHA elicited variable responses in K+ current near threshold voltage, but consistently suppressed conductance at more positive voltages (10-20%).
• PHA's effects on K+ currents could not be explained by surface potential shifts.

Conclusions:

• Potassium (K+) channels are expressed early in T-cell differentiation, potentially before thymic processing.
• Differential PHA-induced responses of K+ currents do not account for the proliferative failure of T3- thymocytes.
• Changes in surface potential are unlikely to be a necessary early event in PHA-mediated T-cell activation.