Bikle D D, Ratnam A, Mauro T, Harris J, Pillai S
Department of Medicine, University of California, San Francisco, California 94121, USA.
J Clin Invest. 1996 Feb 15;97(4):1085-93. doi: 10.1172/JCI118501.
Extracellular calcium concentrations (Cao) > 0.1 mM are required for the differentiation of normal human keratinocytes in culture. Increments in Cao result in acute and sustained increases in the intracellular calcium level (Cai), postulated to involve both a release of calcium from intracellular stores and a subsequent increase in calcium influx through nonspecific cation channels. The sustained rise in Cai appears to be necessary for keratinocyte differentiation. To understand the mechanism by which keratinocytes respond to Cao, we measured the acute effects of Cao on Cai and calcium influx in keratinocytes at various stages of differentiation. We then demonstrated the existence of the calcium receptor (CaR) in keratinocytes and determined the effect of calcium-induced differentiation on its mRNA levels. Finally, we examined the role of Cai in regulating both the initial rise in Cai after the switch to higher Cao and the activity of the nonspecific cation channel through which calcium influx occurs. Our data indicate that the acute Cai response to Cao is lost as the cells differentiate and increase their basal Cai. These data correlated with the decrease in CaR mRNA levels in cells grown in low calcium. However, calcium influx as measured by 45Ca uptake increased with differentiation in 1.2mM calcium, consistent with the increase in CaR mRNA in these cells as well as the calcium-induced opening of the nonspecific cation channels. We conclude that the keratinocyte contains a CaR that regulates both the initial release of Cai from intracellular stores and the subsequent increase in calcium flux through nonspecific calcium channels. A rising level of Cai may turn off the release of calcium from intracellular stores while potentiating the influx through the nonspecific cation channels. Differentiation of keratinocytes appears to increase the CaR, which may facilitate the maintenance of the high Cai required for differentiation.
培养正常人类角质形成细胞的分化需要细胞外钙浓度（Cao）>0.1 mM。Cao的增加会导致细胞内钙水平（Cai）急性且持续升高，推测这涉及细胞内钙库释放钙以及随后通过非特异性阳离子通道的钙内流增加。Cai的持续升高似乎是角质形成细胞分化所必需的。为了解角质形成细胞对Cao作出反应的机制，我们测量了Cao对不同分化阶段角质形成细胞中Cai和钙内流的急性影响。然后我们证明了角质形成细胞中存在钙受体（CaR），并确定了钙诱导分化对其mRNA水平的影响。最后，我们研究了Cai在调节切换到较高Cao后Cai的初始升高以及钙内流所通过的非特异性阳离子通道活性方面的作用。我们的数据表明，随着细胞分化并增加其基础Cai，对Cao的急性Cai反应会丧失。这些数据与低钙培养细胞中CaR mRNA水平的降低相关。然而，以45Ca摄取量衡量的钙内流在1.2 mM钙中随着分化而增加，这与这些细胞中CaR mRNA的增加以及钙诱导的非特异性阳离子通道开放一致。我们得出结论，角质形成细胞含有一种CaR，它调节Cai从细胞内钙库的初始释放以及随后通过非特异性钙通道的钙通量增加。Cai水平的升高可能会关闭细胞内钙库的钙释放，同时增强通过非特异性阳离子通道的内流。角质形成细胞的分化似乎会增加CaR，这可能有助于维持分化所需的高Cai水平。
