Acidic pH-activated Cl<SUP>&#8722;</SUP> Current and Intracellular Ca<SUP>2＋</SUP> Response in Human Keratinocytes

Acidic pH-activated Cl<SUP>&#8722;</SUP> Current and Intracellular Ca<SUP>2＋</SUP> Response in Human Keratinocytes

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^&#8722; current (I_Cl,pH) with slow kinetics of voltage-dependent activation. I_Cl,pHwas potently inhibited by an anion channel blocker 4,4`-diisothiocyanostilbene-2,2`-disulphonic acid (DIDS, 73.5% inhibition at 1&#1356;M). I_Cl,pHbecame more sensitive to pH_e by raising temperature from 24^oC to 37^oC. HaCaT cells also expressed Ca^2＋-activated Cl^&#8722; 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＋] (&#8280;[Ca^2＋]_acid) of HaCaT cells. The &#8280;[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 &#8280;[Ca^2＋]_acid. In summary, we found I_Cl,pH and &#8280;[Ca^2＋]_acid in human keratinocytes, and these ionic signals might have implication in pathophysiological responses and differentiation of epidermal keratinocytes.