I-KIR REGULATION IN MURINE MACROPHAGES - WHOLE-CELL AND PERFORATED-PATCH STUDIES

Previous studies have reported that the inwardly rectifying Kt conduct ance (G(Kir)) in macrophages is modulated by intracellular perfusion w ith inositol 1,4,5-trisphosphate (InsP(3)), inositol 1,3,4,5-tetrakisp hosphate (InsP(4)), or GTP analogues and by exposing cells to macropha ge-specific colony-stimulating factor (CSF) I. This study uses both co nventional whole cell and amphotericin B perforated patch studies to i nvestigate G(Kir) modulation in thioglycollate-elicited mouse peritone al macrophages (M theta). Under whole cell recording conditions with 1 50 mM Cl- in the patch pipette, G(Kir) decreased within 25 min. The G( Kir) decrease was slowed by exchanging glutamate for Cl- as the major anion in the pipette or by adding guanosine 5'-O-(2-thiodiphosphate) ( 50 nM) or ATP (0.5 mM) to the pipette. Addition of InsP(3) or InsP(4) to the pipette had no effect on the magnitude of G(Kir) or its rate of decrease but activated an outward current in the voltage range of +60 to +120 mV in 57% of the cells studied. Thus in murine M theta G(Kir) may be modulated by G proteins but is unaffected by inositol phosphat e metabolites, which have been reported to enhance G(Kir) in phorbol 1 2-myristate 13-acetate (PMA)-differentiated HL-60 cells. In contrast t o whole cell studies, perforated patch recordings of murine M theta G( Kir) were stable for >1 h. Perforated patch studies demonstrated that murine M theta also differ from PMA-differentiated HL-60 cells in that CSF I had no effect on G(Kir) Additionally, arachidonic acid, PMA, an d H2O2, agents implicated in macrophage activation, did not modulate G (Kir) We conclude that G(Kir) regulation in murine M theta differs fro m that reported in PMA-differentiated HL-60 cells and that although ou r data suggest that G(Kir) is modulated by G protein(s), they differ f rom the G proteins involved in M theta responses to CSF I and the othe r agents tested.