Human keratinocytes respond to direct current stimulation by increasing intracellular calcium: preferential response of poorly differentiated cells.

A direct current (DC) endogenous electric field (EF) is induced in the wound following skin injury. It is potentially implicated in the wound healing process by attracting cells and altering their phenotypes as indicated by the response to an EF of keratinocytes cultured as individual cells. To better define the signalization induced by a direct current electric field (DCEF) in human keratinocytes, we took advantage of an in vitro model more representative of the in vivo situation since it promotes cell-cell interactions and stratification. Human keratinocytes were grown into colonies. Their exposure to a DCEF of physiological intensity induced an increase of intracellular calcium. This variation of intracellular calcium resulted from an extracellular calcium influx and was mediated, at least in part, by the L-type voltage-gated calcium channel. The increase in intracellular calcium in response to a DCEF was however not observed in all the cells composing the colonies. The intracellular calcium increase was only detected in keratinocytes that didn't express involucrin, a marker of differentiated cells. These results indicate that DCEF is able to induce a specific calcium response in poorly differentiated keratinocytes. This study brings a new perspective for the understanding of the signaling mechanism of endogenous EF in reepithelialization, a critical process during skin wound healing.

Electric Potential Across Epidermis and Its Role During Wound Healing Can Be Studied by Using an In Vitro Reconstructed Human Skin.

BACKGROUND: After human epidermis wounding, transepithelial potential (TEP) present in nonlesional epidermis decreases and induces an endogenous direct current epithelial electric field (EEF) that could be implicated in the wound re-epithelialization. Some studies suggest that exogenous electric stimulation of wounds can stimulate healing, although the mechanisms remain to be determined. THE PROBLEM: Little is known concerning the exact action of the EEF during healing. The mechanism responsible for TEP and EEF is unknown due to the lack of an in vitro model to study this phenomenon. BASIC SCIENCE ADVANCES: We carried out studies by using a wound created in a human tissue-engineered skin and determined that TEP undergoes ascending and decreasing phases during the epithelium formation. The in vitro TEP measurements over time in the wound were corroborated with histological changes and with in vivo TEP variations during porcine skin wound healing. The expression of a crucial element implicated in Na+ transport, Na+/K+ ATPase pumps, was also evaluated at the same time points during the re-epithelialization process. The ascending and decreasing TEP values were correlated with changes in the expression of these pumps. The distribution of Na+/K+ ATPase pumps also varied according to epidermal differentiation. Further, inhibition of the pump activity induced a significant decrease of the TEP and of the re-epithelization rate. CLINICAL CARE RELEVANCE: A better comprehension of the role of EEF could have important future medical applications regarding the treatment of chronic wound healing. CONCLUSION: This study brings a new perspective to understand the formation and restoration of TEP during the cutaneous wound healing process.

Restoration of the transepithelial potential within tissue-engineered human skin in vitro and during the wound healing process in vivo.

Normal human epidermis possesses a transepithelial potential (TEP) that varies in different parts of the body (10­60mV). The role of TEP in normal epidermis is not yet identified; but after skin injury, TEP disruption induces an endogenous direct current electric field (100­200mV/mm) directed toward the middle of the wound. This endogenous electric field could be implicated in the wound healing process by attracting cells, thus facilitating reepithelialization. However, little is known on the restoration of the TEP during human skin formation and wound healing. In this study, the variations in TEP and Na+/K+ ATPase pump expression during the formation of the epithelium were investigated in vitro using human tissue-engineered human skin (TES) reconstituted by tissue engineering and in vivo with a porcine wound healing model. Results showed that TEP undergoes ascending and decreasing phases during epithelium formation in TES as well as during wound repair within TES. Similar results were observed during in vivo reepithelialization of wounds. The ascending and decreasing TEP values were correlated with changes in the expression of Na+/K+ ATPase pump. The distribution of Na+/K+ ATPase pumps also varied according to epidermal differentiation. Taken together, these results suggest that the variations in the expression of Na+/K+ ATPase pump over time and across epidermis would be a determinant parameter of the TEP, dictating a cationic transport during the formation and restoration of the epidermis. Therefore, this study brings a new perspective to understand the formation and restoration of TEP during the cutaneous wound healing process. This might have important future medical applications regarding the treatment of chronic wound healing.

Experimental validation of a statistical model for evaluating the past or future magnetic field exposures of a population living near power lines.

This study was designed to provide an experimental validation for a statistical model predicting past or future exposures to magnetic fields (MF) from power lines. The model estimates exposure, combining the distribution of ambient MF in the absence of power lines with the distribution of past or future MF produced by power lines. In the study, validation is carried out by comparing exposures predicted by the model with the actual measurements obtained from a large-scale epidemiological study. The comparison was made for a group of 220 women living near a 735 kV power line. Knowing that the individual arithmetic means of MF exposures follow a log-normal distribution, the Pearson correlation between the log-transformed measured means and the calculated ones was determined and found to be 0.77. Predicted values of MF exposures were slightly lower than measured values. The calculated geometric mean of the group was 0.33 microT, compared to 0.38 microT for the measured geometric mean. The present study shows good agreement between the measured MF exposure of an individual inside a house near a 735 kV line and the MF exposure calculated using a statistical model.