A large conductance [Ca(2+)](i)-independent K(+) channel expressed in HaCaT keratinocytes

Latest Insights into the In Vivo Studies in Murine Regarding the Role of TRP Channels in Wound Healing-A Review

Wound healing involves physical, chemical and immunological processes. Transient receptor potential (TRP) and other ion channels are implicated in epidermal re-epithelization. Ion movement across ion channels can induce transmembrane potential that leads to transepithelial potential (TEP) changes. TEP is present in epidermis surrounding the lesion decreases and induces an endogenous direct current generating an epithelial electric field (EF) that could be implicated in wound re-epithelialization. TRP channels are involved in the activation of immune cells during mainly the inflammatory phase of wound healing. The aim of the study was to review the mechanisms of ion channel involvement in wound healing in in vivo experiments in murine (mice, rats) and how can this process be influenced. This review used the latest results published in scientific journals over the last year and this year to date (1 January 2023-31 December 3000) in order to include the in-press articles. Some types of TRP channels, such as TRPV1, TRPV3 and TRPA1, are expressed in immune cells and can be activated by inflammatory mediators. The most beneficial effects in wound healing are produced using agonists of TRPV1, TRPV4 and TRPA1 channels or by inhibiting with antagonists, antisense oligonucleotides or knocking down TRPV3 and TRPM8 channels.

Enhancing Human Cutaneous Wound Healing through Targeted Suppression of Large Conductance Ca2+-Activated K+ Channels

The modulation of K+ channels plays a crucial role in cell migration and proliferation, but the effect of K+ channels on human cutaneous wound healing (CWH) remains underexplored. This study aimed to determine the necessity of modulating K+ channel activity and expression for human CWH. The use of 25 mM KCl as a K+ channel blocker markedly improved wound healing in vitro (in keratinocytes and fibroblasts) and in vivo (in rat and porcine models). K+ channel blockers, such as quinine and tetraethylammonium, aided in vitro wound healing, while Ba2+ was the exception and did not show similar effects. Single-channel recordings revealed that the Ba2+-insensitive large conductance Ca2+-activated K+ (BKCa) channel was predominantly present in human keratinocytes. NS1619, an opener of the BKCa channel, hindered wound healing processes like proliferation, migration, and filopodia formation. Conversely, charybdotoxin and iberiotoxin, which are BKCa channel blockers, dramatically enhanced these processes. The downregulation of BKCa also improved CWH, whereas its overexpression impeded these healing processes. These findings underscore the facilitative effect of BKCa channel suppression on CWH, proposing BKCa channels as potential molecular targets for enhancing human cutaneous wound healing.

KATP channel block inhibits the Toll-like receptor 2-mediated stimulation of NF-κB by suppressing the activation of Akt, mTOR, JNK and p38-MAPK

Changes in the K_ATP channel activity have been shown to regulate inflammation and immune responses. Using human keratinocytes, we investigated the effect of K_ATP channel inhibition on inflammatory mediator production in relation to the Toll like receptor-2-mediated-Akt, mTOR and NF-κB pathways, as well as JNK and p38-MAPK, which regulate the transcription genes involved in immune and inflammatory responses. 5-Hydroxydecanoate (a selective K_ATP channel blocker), glibenclamide (a cell surface and mitochondrial K_ATP channel inhibitor), the Akt inhibitor, rapamycin, Bay 11-7085 and N-acetylcysteine reduced the lipoteichoic acid- or peptidoglycan-induced production of cytokines and chemokines, and production of reactive oxygen species and increased the levels and activities of Kir 6.2, NF-κB, phosphorylated-Akt and mTOR, and the activation of JNK and p38-MAPK in keratinocytes. Inhibitors of c-JNK (SP600125) and p38-MAPK (SB203580) attenuated the lipoteichoic acid- or peptidoglycan-induced production of inflammatory mediators, the activation of the JNK and p38-MAPK, and the production of reactive oxygen species in keratinocytes. The results show that K_ATP channel blockers may reduce the bacterial component-stimulated production of inflammatory mediators in keratinocytes by suppressing the Toll-like receptor-2-mediated activation of the Akt, mTOR and NF-κB pathways, as well as JNK and p38-MAPK. The suppressive effect of K_ATP channel blockers appears to be achieved by the inhibition of reactive oxygen species production.

Potassium channel in the mitochondria of human keratinocytes

The activation of mitochondrial potassium channels induces cytoprotection in various cell types. Hence, the identification of ion channels present in the inner mitochondrial membrane of keratinocytes is important in distinguishing possible protective mechanisms in these cells. In this paper, inner membrane mitochondrial ion channels of the human keratinocyte HaCaT cell line were investigated using a patch-clamp technique. We observed potassium-selective channel activity with a conductance of 83 pS at positive voltages. The I-V curve indicates that the observed channel has rectifying properties. Moreover, the channel activity was inhibited by acidic pH and 1 mM lidocaine. Using reverse transcriptase-PCR, we found an mRNA transcript for the TASK-3 (tandem pore domain acid-sensitive K channels) channel. We observed co-localization of the TASK-3 protein and a mitochondrial marker in the mitochondria of HaCaT cells. Additionally, we showed that TASK-3 knockdown HaCaT cells markedly decreased viability after UVB radiation exposure compared with control cells. In summary, the single-channel activity and properties of a mitochondrial potassium channel in a keratinocyte HaCaT cell line have been described.

The channel physiology of the skin

During embryonic development, the skin, the largest organ of the human body, and nervous system are both derived from the neuroectoderm. Consequently, several key factors and mechanisms that influence and control central or peripheral nervous system activities are also present and hence involved in various regulatory mechanisms of the skin. Apparently, this is the case for the ion and non-ion selective channels as well. Therefore, in this review, we shall focus on delineating the regulatory roles of the channels in skin physiology and pathophysiology. First, we introduce key cutaneous functions and major characteristics of the channels in question. Then, we systematically detail the involvement of a multitude of channels in such skin processes (e.g. skin barrier formation, maintenance, and repair, immune mechanisms, exocrine secretion) which are mostly defined by cutaneous non-neuronal cell populations. Finally, we close by summarizing data suggesting that selected channels are also involved in skin diseases such as e.g. atopic dermatitis, psoriasis, non-melanoma cancers and malignant melanoma, genetic and autoimmune diseases, etc., as well as in skin ageing.

Characterization of large-conductance Ca2+-dependent and -independent K+ channels in HaCaT keratinocytes

To characterize ion channels expressed in cell membrane of human keratinocytes, patch-clamp recordings were carried out in HaCaT cells. Two types of large-conductance K(+) channels (about 250 pS) were measured. One type was activated by micromolar concentrations of intracellular Ca(2+) ions ([Ca(2+)](i)) and membrane depolarization, the other was [Ca(2+)](i) independent. The channels were neither dependent on intracellular ATP nor Mg(2+) nor on membrane stretch. We conclude that HaCaT keratinocytes express Ca(2+)-dependent maxi K(+) channels and still unknown large Ca(2+)-independent K(+) channels. These K(+) channels may affect the proliferation and differentiation of human keratinocytes by the influence on the resting potential, which may control the Ca(2+) influx across the cell membrane.

Properties of BK(Ca) channels in oral keratinocytes

Keratinocytes are important for epithelial antimicrobial barrier function. The activity of ion channels can affect the proliferation of keratinocytes. Little is known about Ca2+-activated K+ currents in these cells. Ion currents in normal human oral keratinocytes were characterized with a patch-clamp technique. In whole-cell configuration, depolarizing pulses evoked K+ outward currents (I(K)) in oral keratinocytes. Iberiotoxin (200 nM) and paxilline (1 microM) suppressed I(K); however, neither apamin (200 nM) nor 5-hydroxydecanoate (30 microM) had any effects on it. Caffeic acid phenethyl ester, a compound of honeybee propolis, increased I(K) with an EC50 value of 12.8 +/- 1.2 microM. In inside-out patches, a BK(Ca) channel was observed in keratinocytes, but not in oral squamous carcinoma (OCE-M1) cells. Caffeic acid phenethyl ester or cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate applied to the intracellular surface of a detached patch increased BK(Ca)-channel activity. The results demonstrate that the properties of BK(Ca) channels in normal human oral keratinocytes are similar to those described in other types of cells. Caffeic acid derivatives can also stimulate BK(Ca)-channel activity directly.

Cell-cycle-dependent expression of the large Ca2+-activated K+ channels in breast cancer cells

In a previous work, we have reported that the ionic nature of the outward current recorded in MCF-7 cells was that of a K+ current. In this study, we have identified a Ca2+-activated K+ channel not yet described in MCF-7 human breast cancer cells. In cells arrested in the early G1 (depolarized cells), increasing [Ca2+]i induced both a shift in the I-V curve toward more negative potentials and an increase in current amplitude at negative and more at positive potential. Currents were inhibited by r-iberiotoxin (r-IbTX, 50 nM) and charybdotoxin (ChTX, 50 nM). These data indicate that human breast cancer cells express large-conductance Ca2+-activated K+ (BK) channels. BK current-density increased in cells synchronized at the end of G1, as compared with those in the early G1 phase. This increased current-density paralleled the enhancement in BK mRNA levels. Blocking BK channels with r-IbTX, ChTX or both induced a slight depolarization in cells arrested in the early G1, late G1, and S phases and accumulated cells in the S phase, but failed to induce cell proliferation. Thus, the expression of the BK channels was cell-cycle-dependent and seems to contribute more to the S phase than to the G1 phase. However, these K+ channels did not regulate the cell proliferation because of their minor role in the membrane potential.