HISTAMINE MODULATES 3 TYPES OF K+ CURRENT IN A HUMAN INTESTINAL EPITHELIAL-CELL LINE

K+ conductance species in a human intestinal epithelial cell line (Intestine 407) were studied in connection with their sensitivities to an intestinal secretagogue, histamine, using the tight-seal whole-cell patch-clamp technique. Applications of positive command pulses rapidly induced outward K+ currents. The conductance became progressively larger with increasing command voltages, exhibiting an outwardly rectifying current voltage relation. Inward K+ currents were also rapidly activated upon applications of hyperpolarizing pulses at potentials negative to the equilibrium potential of K+ (E(K)), and the conductance inwardly rectified. Application of a Ca2+ ionophore, ionomycin, brought about activation of additional K+ currents. An inhibitor of protein kinase C, polymyxin B, did not affect the ionomycin-induced response. Histamine (10-200 mu M) also activated a similar K+ current which was abolished by cytosolic Ca2+ chelation. Under conditions where Ca2+ mobilization was minimized, histamine was found to significantly augment inwardly rectifying K+, but suppress outwardly rectifying K+, currents. Polymyxin B blocked these effects of histamine. An activator of protein kinase C, 1-oleoyl-2-acetylglycerol, mimicked the histamine effects. It is concluded that the intestinal epithelial cell has three distinct types of K+ conductance and that histamine modulates not only Ca2+-activated K+ conductance via Ca2+ mobilization, but also inward- and outward-rectifier K+ conductances via activation of protein kinase C.