We have used the human calcium- and temperature-dependent (HaCaT) keratinocyte cell line to elucidate mechanisms of switching from a proliferating to a differentiating state. When grown in low calcium medium (<0.1 mM) HaCaT cells proliferate. However, an increase in the calcium concentration of the culture medium, [Ca(2+)](0), induces growth arrest and the cells start to differentiate. Numerous studies have already shown that the increase in [Ca(2+)](0) results in acute and sustained increases in intracellular calcium concentration, [Ca(2+)](i). We find that the Ca(2+)-induced cell differentiation of HaCaT cells is also accompanied by a significant decrease in mitochondrial membrane potential, DeltaPsi. By combining patch-clamp electrophysiological recordings and microspectrofluorimetric measurements of DeltaPsi on single cells, we show that the increase in [Ca(2+)](i) led to DeltaPsi depolarization. In addition, we report that tetraethylammonium (TEA), a blocker of plasma membrane K(+) channels, which is known to inhibit cell proliferation, and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), a blocker of plasma membrane Cl(-) channels, also affect DeltaPsi. Both these agents stimulate HaCaT cell differentiation. These data therefore strongly suggest a direct causal relationship between depolarization of DeltaPsi and the inhibition of proliferation and induction of differentiation in HaCaT keratinocytes.

Calcium↗

PubMedDate not supplied

[Electrophysiologic definition of sensory integration in the aphasic, (Evoked potentials, Slow potentials)].

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Aphasia↗

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Dopamine inhibition of action potentials in a prolactin secreting cell line is modulated by oestrogen.

Secretory activity of the anterior pituitary gland is regulated by the brain through stimulatory and inhibitory substances released from nerve endings in the median eminence of the hypothalamus and carried by the adenohypophysial portal blood system to their respective target cells. These hypothalamic influences are modulated by the feedback action of peripheral hormones. Prolactin (PRL) secreting cells are, at least partially, under the stimulatory influence of thyrotropin releasing hromone (TRH) and of oestrogens. However, they are mainly controlled by inhibitory substances among which dopamine (DA) is one of the most potent in vivo as well as in vitro. The inhibitory effect of DA is reversed by oestrogen in vitro. The mechanism by which these factors interact on their target cells is poorly understood. The recent discovery that anterior pituitary cells are excitable and that they are able to generate Ca2+-dependent action potentials has led to the suggestion that these effects are involved in a stimulus-secretion coupling at the membrane level. In this paper, we report that DA inhibits both the spontaneous and TRH-induced action potentials in clonal PRL pituitary cells. In addition, oestradiol-17 beta is able to reverse the inhibitory effect of DA.

Action Potentials↗