Endotoxin-Induced L-Arginine Pathway Produces Nitric Oxide and Modulates the Ca2+-Activated K+ Channel in Cultured Human Dermal Papilla Cells

Abstract

Endotoxin induces an enzyme that synthesizes nitric oxide (NO) from L-arginine (NO synthase) in vascular smooth muscle cells, macrophages, and fibroblasts, leading to the release of NO. We evaluated the release of NO and its intracellular action on the Ca2+-activated K+ channel (KCa channel) in cultured human dermal papilla cells by use of the electron paramagnetic response (EPR) spin trapping method and the patch clamp technique. In dermal papilla cells pretreated for 24 h with endotoxin (1 μg/ml), application of 1 mM L-arginine generated NO, although 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 KCa channel of dermal papilla cells had high conductance and was voltage dependent. In addition, after endotoxin pretreatment, the extracellular application of 100 μM L-arginine modulated the KCa channel in the cell-attached patch configurations. In inside-out patch configuration, however, NO produced by L-arginine itself did not modulate the KCa channel. This modulation of the KCa channel was suppressed by pretreatment with 100 μM Nω-nitro-L-arginine methyl ester, an inhibitor of inducible and constitutive NO synthases. Methylene blue, a blocker of guanylate cyclase, inhibited the L-arginine-induced activation of the KCa channel. These results indicate that the endotoxin-induced L-arginine pathway generates NO, which consequently modulates the KCa channel in cultured human dermal papilla cells by increasing of cyclic GMP-dependent phosphorylation.