Acidic pH-activated Cl- Current and Intracellular Ca2+ Response in Human Keratinocytes

Abstract

The layers of keratinocytes form an acid mantle on the surface of the skin. Herein, we investigated the effects of acidic pH on the membrane current and [Ca(2+)](c) of human primary keratinocytes from foreskins and human keratinocyte cell line (HaCaT). Acidic extracellular pH (pH(e)</= 5.5) activated outwardly rectifying Cl(-) current (I(Cl,pH)) with slow kinetics of voltage-dependent activation. I(Cl,pH) was potently inhibited by an anion channel blocker 4,4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS, 73.5% inhibition at 1 microM). I(Cl,pH) became more sensitive to pH(e) by raising temperature from 24 to 37. HaCaT cells also expressed Ca(2+)-activated Cl(-) current (I(Cl,Ca)), and the amplitude of I(Cl,Ca) was increased by relatively weak acidic pH(e) (7.0 and 6.8). Interestingly, the acidic pH(e) (5.0) also induced a sharp increase in the intracellular [Ca(2+)] (Delta[Ca(2+)](acid)) of HaCaT cells. The Delta[Ca(2+)](acid) was independent of extracellular Ca(2+), and was abolished by the pretreatment with PLC inhibitor, U73122. In primary human keratinocytes, 5 out of 28 tested cells showed Delta[Ca(2+)](acid). In summary, we found I(Cl,pH) and Delta[Ca(2+)](acid) in human keratinocytes, and these ionic signals might have implication in pathophysiological responses and differentiation of epidermal keratinocytes.