Using intracellular Ca²⁺ imaging and patch-clamp techniques we investigated the effects of histamine, ATP, cell swelling induced by hypotonic solution (HTS; 200 mosmol/l) and thapsigargin (TG)-induced store-operated Ca²⁺ entry (SOCE) on chloride currents in human keratinocytes (an immortalized, non-tumour HaCaT cell line). The effects of ATP and histamine were of primarily interest since HaCaT cells express H₂ histamine and P2Y2 purinergic receptors coupled to the phosphoinositide pathway and since keratinocytes are typically exposed to these substances during skin injury, inflammatory skin diseases and allergic reactions. In intact cells receptor agonists as well as TG induced a transient elevation of [Ca²⁺]_i in a Ca²⁺-free medium followed by a secondary [Ca²⁺]_i rise upon Ca²⁺ readmission due to SOCE. Agonists activated two kinetically distinct currents which showed different voltage dependence and were identified as Ca²⁺-activated (I_Cl(Ca)) and volume-regulated (I_Cl,swell) chloride currents. At 100 μM 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and 4,4′-diisothiocyanato-stilbene-2,2′-disulfonic acid (DIDS) more efficiently inhibited I_Cl(Ca) and I_Cl,swell, respectively (90±9% vs. 58±3% inhibition of I_Cl(Ca) and 33±14% vs. 97±2% inhibition of I_Cl,swell by NPPB and DIDS, respectively; n=4). The PLC inhibitor U-73122 blocked both agonist- and cell swelling-induced I_Cl,swell (at 1 μM by 72±14%; n=5 and 75±4%; n=3, respectively) while its inactive analogue U-73343 had no effect. I_Cl,swell could be directly activated by OAG, a cell-permeable diacylglycerol analogue, but not by InsP₃ infusion; protein kinase C also had no role in its regulation. Agonists had no effect on 100 μM OAG-induced current while HTS-induced current was insensitive to both agonists and OAG (in all cases current amplitude changed by less than 5%). Thus, agonists, OAG and cell swelling induced I_Cl,swell in a non-additive manner suggesting their convergence on a common pathway. Moreover, both I_Cl,swell and I_Cl(Ca) showed no or very little overlap (i.e. simultaneous activation) although various manoeuvres could induce these currents sequentially in the same cell. TG-induced SOCE strongly potentiated I_Cl(Ca) but abolished I_Cl,swell providing a clue for this paradox. Thus, we have established for the first time using keratinocyte model that I_Cl,swell can be physiologically activated under isotonic conditions by receptors coupled to the phosphoinositide pathway. These results also suggest a novel function for SOCE which can operate as a “selection” switch between closely localized channels; this way cells can translate a graded Ca²⁺ entry via SOC channels into different ion channel responses.