ENDOTOXIN-INDUCED L-ARGININE PATHWAY PRODUCES NITRIC-OXIDE MODULATES THE CA2-ACTIVATED K+ CHANNEL IN CULTURED HUMAN DERMAL PAPILLA CELLS()

Endotoxin induces an enzyme that synthesizes nitric oxide (NO) from L- arginine (NO synthase) in vascular smooth muscle cells, macrophages, a nd fibroblasts, leading to the release of NO, We evaluated the release of NO and its intracellular action on the Ca2+-activated K+ channel ( K-Ca channel) in cultured human dermal papilla cells by use of the ele ctron paramagnetic response (EPR) spin trapping method and the patch c lamp technique, In dermal papilla cells pretreated for 24 h with endot oxin (1 mu g/ml), application of 1 mM L-arginine generated NO, althoug h no measurable release of NO was observed in cells without endotoxin pretreatment, as determined by the EPR spin trapping method. With the patch clamp technique, we found that the K-Ca channel of dermal papill a cells had high conductance and was voltage dependent. In addition, a fter endotoxin pretreatment, the extracellular application of 100 mu M L-arginine modulated the K-Ca channel in the cell-attached patch conf igurations. In inside-out patch configuration, however, NO produced by L-arginine itself did not modulate the K-Ca channel. This modulation of the K-Ca channel was suppressed by pretreatment with 100 mu M N-ome ga-nitro-L-arginine methyl ester, an inhibitor of inducible and consti tutive NO synthases. Methylene blue, a blocker of guanylate cyclase, i nhibited the L-arginine-induced activation of the K-Ca channel, These results indicate that the endotoxin-induced L-arginine pathway generat es NO, which consequently modulates the K-Ca channel in cultured human dermal papilla cells by increasing of cyclic GMP-dependent phosphoryl ation.