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Epidermal cells, such as keratinocytes, are regarded as the first sensory cells to transmit nociception and mechanoreception to free nerve endings extended from the dorsal root ganglion (DRG). Previous studies suggested that this transmission occurs as Ca2+ propagation via ATP receptors. Conversely, the influence of gap junctions on this Ca2+ propagation is largely unknown. Thus, we examined the localization and the role of connexin 43 among keratinocytes and DRG neurons. We co-cultured keratinocytes and DRG neurons and investigated the effect of pharmacological blockade of gap junctions on Ca2+ propagation upon stimulation of a single keratinocyte. Immunocytochemical experiments showed that connexin 43 is localized between keratinocytes and between keratinocytes and DRG neurons. Octanol, a gap junction inhibitor, significantly suppressed the concentrical Ca2+ propagation. Therefore, we conclude that the Ca2+ propagation mechanism via gap junctions from stimulated keratinocytes to free nerve endings should be taken into account. [ABSTRACT FROM AUTHOR]

As human-origin cells, human dental pulp stem cells (hDPSCs) are thought to be potentially useful for biological and medical experiments. They are easily obtained from lost primary teeth or extracted wisdom teeth, and they are mesenchymal stem cells that are known to differentiate into osteoblasts, chondrocytes, and adipocytes. Although hDPSCs originate from neural crest cells, it is difficult to induce hDPSCs to differentiate into neuron-like cells. To facilitate their differentiation into neuron-like cells, we evaluated various differentiation conditions. Activation of K+ channels is thought to regulate the intracellular Ca2+ concentration, allowing for manipulation of the cell cycle to induce the differentiation of hDPSCs. Therefore, in addition to a conventional neural cell differentiation protocol, we activated K+ channels in hDPSCs. Immunocytochemistry and real-time PCR revealed that applying a combination of 3 stimuli (high K+ solution, epigenetic reprogramming solution, and neural differentiation solution) to hDPSCs increased their expression of neuronal markers, such as ß3-tubulin, postsynaptic density protein 95, and nestin within 5 days, which led to their rapid differentiation into neuron-like cells. Our findings indicate that epigenetic reprogramming along with cell cycle regulation by stimulation with high K+ accelerated the differentiation of hDPSCs into neuronlike cells. Therefore, hDPSCs can be used in various ways as neuron-like cells by manipulating their cell cycle. [ABSTRACT FROM AUTHOR]