Expression of Ca-Activated K+ Channels in Human Dermal Fibroblasts and Their Roles in Apoptosis

Backgrounds/Aims: 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 Ca2+-activated K+ (KCa) channels has been demonstrated in many types of tissues, but not in dermal fibroblasts. We investigated the expression of KCa channels and their effects on proliferation and apoptosis in human dermal fibroblasts. Methods: 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 KCa channel family, large-conductance KCa (BK), intermediate-conductance KCa (IK) and small-conductance KCa 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 KCa channels on cell proliferation and the mechanisms involved. Results and Conclusions: All 3 members of the KCa 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 KCa 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. Copyright © 2009 S. Karger AG, Basel [PUBLICATION ABSTRACT]