Development of a delayed outward-rectifying K+ conductance in cultured mouse peritoneal macrophages.

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Abstract
Patch clamp techniques were used to study ionic currents in cultured mouse peritoneal macrophages. Whole-cell voltage clamp studies of cells 1-5 h after isolation showed only a high-resistance linear membrane. After 1 day in culture, 82 of 85 cells studied had developed a voltage- and time-dependent K+ conductance similar to the delayed outward rectifier in nerve and muscle cells. The current activated when the membrane was depolarized above -50 mV. The sigmoidally rising current rose to a peak at a rate that increased with depolarization. Inactivation proceeded exponentially with a time constant of .apprxeq. 450 ms. Recovery from inactivation was slow (.tau. = 12 s). The reversal potentials for varying extracellular K+ concentrations followed the Nernst predictions for a K+-specific channel. The conductance was blocked by extracellular 4-aminopyridine and by intracellular tetraethylammonium chloride, Ba and Cs. Single-channel K+ currents comprising this net current had a conductance of 16 pS, exhibited bursting behavior, and inactivated with time. No inward currents were ever detcted in macrophages cultivated for up to 4 days. Short-term exposure to chemoattractant and transmitter agents failed to activate an inward current. Macrophages may change their membrane electrophysiological properties depending on their state of functional activation. The K+ conductance may develop prior to depolarizing conductances involved in the macrophage''s immunological functions.