Ionic channels and membrane hyperpolarization in human macrophages

Microelectrode impalement of human macrophages evokes a transient hyperpolarizing response (HR) of the membrane potential. This HR was found to be dependent on the extracellular concentration of K+ but not on that of Na+ or Cl-. It was not influenced by low temperature (12 degrees C) or by 0.2 mM ouabain, but was blocked by 0.2 mM quinine or 0.2 mM Mg2+-EGTA. These findings indicate that the HR in human macrophages is caused by the activation of a K+ (Ca2+) conductance. Two types of ionic channels were identified in intact cells by use of the patch-clamp technique in the cell-attached-patch configuration, low and high-conductance voltage-dependent K+ channels. The low-conductance channels had a mean conductance of 38 pS with Na+-saline and 32 pS with K+-saline in the pipette. The high-conductance channels had a conductance of 101 and 114 pS with Na+- and K+-saline in the pipette, respectively. Cell-attached patch measurements made during evocation of an HR by microelectrode penetration showed enhanced channel activity associated with the development of the HR. These channels were also high-conductance channels (171 pS with Na+- and 165 pS K+-saline in the pipette) and were voltage dependent. They were, however, active at less positive potentials than the high-conductance K+ channels seen prior to the microelectrode-evoked HR. It is concluded that the high-conductance voltage-dependent ionic channels active during the HR in human macrophages contribute to the development of the HR