A negative resistance region underlies the triggering property of membrane potential in human T-lymphocytes.

Steady-state current-voltage relationships (SSCVRs) of the plasma membrane of human T-lymphocytes were studied at the physiological temperature of 37 degrees C by using the whole-cell patch-clamp technique. SSCVRs displayed a characteristic N-like shape with a negative resistance region (NRR) in a voltage range of -45 to -35 mV. The majority of cells assayed revealed SSCVR patterns crossing the V-axis at three points (in mV): V1 = -55 to -45, V2 = -40 to -35, V3 = -30 to -10. SSCVRs of T-cells activated by phytohaemagglutinin (48-96 h) also displayed NRR, but crossed the V-axis at one point only (V1 = -55 to -60 mV). It implies the possibility of two stable levels of membrane potential (V1 and V3) for the resting T-cells, but only one (V1) for activated T-cells. These data thus account for the triggering property of T-cell membrane potential previously reported. The NRR can be explained on the basis of the Hodgkin-Huxley type n4j model of K+ channel kinetics. According to the model the possibility for a membrane to have one or two stable levels of membrane potential depends on the ratio of selective K+ conductance to non-selective leaky conductance (Gk/G(leak)). The steady-state level of K+ conductance in resting T-lymphocytes proved to be sensitive to Ca2+. Buffering Ca2+ ions from either external or internal solution resulted in an appreciable increase in K+ conductance. The possibility for membrane potential to have two stable levels of membrane potential in connection with the Ca2+ dependence of K+ conductance was supposed to be important for Ca(2+)-signalling during T-cell activation.