Expression of Ca2+ -activated K+ channels in human dermal fibroblasts and their roles in apoptosis

Cell proliferation and apoptosis are responsible for maintaining normal tissue homeostasis, and K(+) currents play important roles in regulating the physiological balance between them. This function of Ca(2+)-activated K(+) (K(Ca)) channels has been demonstrated in many types of tissues, but not in dermal fibroblasts. We investigated the expression of K(Ca) channels and their effects on proliferation and apoptosis in human dermal fibroblasts.

We used discoidin domain receptor 2 immunostaining to identify human dermal fibroblasts, and reverse transcription polymerase chain reaction, Western blot analysis and electrophysiological patch clamp recordings to evaluate the expression and characteristics of 3 members of the K(Ca) channel family, large-conductance K(Ca) (BK), intermediate-conductance K(Ca) (IK) and small-conductance K(Ca) channels. We also used the 3-(4,5-dimethyl-2-yl)-2,5-diphenyltetrazolium bromide assay, flow cytometry, Hoechst 33258 staining and Depsipher staining to investigate the effects of K(Ca) channels on cell proliferation and the mechanisms involved.

All 3 members of the K(Ca) channel family were found in fibroblasts. 1,3-Dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS1619, a BK channel activator) or 1-ethyl-2-benzimidazolinone (EBIO, an IK channel activator) decreased the proliferation of fibroblasts and induced apoptotic changes by mitochondrial membrane potential disruption. However, a pan-caspase inhibitor (Z-VAD-fmk) failed to prevent the apoptotic changes. Our findings indicate that 3 types of functional K(Ca) channels are expressed in human dermal fibroblasts and are involved in apoptosis of the cells through the mitochondrial apoptotic pathway, but seemingly in a caspase-independent manner.