Properties of BK_Ca channels in oral keratinocytes

Keratinocytes are important for epithelial antimicrobial barrier function. The activity of ion channels can affect the proliferation of keratinocytes. Little is known about Ca²⁺-activated K⁺ currents in these cells. Ion currents in normal human oral keratinocytes were characterized with a patch-clamp technique. In whole-cell configuration, depolarizing pulses evoked K⁺ outward currents (i_K) in oral keratinocytes. Iberiotoxin (200 nM) and paxilline (1 μM) suppressed I_K; however, neither apamin (200 nM) nor 5-hydroxydecanoate (30 μM) had any effects on it. Caffeic acid phenethyl ester, a compound of honeybee propolis, increased I _K with an EC₅₀ value of 12.8 ± 1.2 μM. In inside-out patches, a BK_Ca channel was observed in keratinocytes, but not in oral squamous carcinoma (OCE-M1) cells. Caffeic acid phenethyl ester or cinnamyl-3,4-dihydroxy-α-cyanocinnamate applied to the intracellular surface of a detached patch increased BK_Ca-channel activity. The results demonstrate that the properties of BK_Ca channels in normal human oral keratinocytes are similar to those described in other types of cells. Caffeic acid derivatives can also stimulate BK_Ca-channel activity directly.