Calcium channel kinetics of melanotrope cells in Xenopus laevis depend on environmental stimulation

Abstract We have tested the hypothesis that the type and kinetics of voltage-activated Ca2+ channels in a neuroendocrine cell depend on the cell’s long-term external input. For this purpose, the presence and kinetics of both low (LVA) and high-voltage-activated (HVA) L-type Ca2+ channels have been assessed in melanotrope pituitary cells of the amphibian Xenopus laevis . The secretory activity of this cell type can readily be manipulated in vivo by changing the animal’s environmental light condition, from a black to a white background. We here show that, compared to white background-adapted Xenopus , melanotropes from black background-adapted frogs have (1) a much larger size, as revealed by their 2.5 times larger membrane capacitance ( P < 0.001), (2) a 2 times higher HVA current density ( P < 0.05), (3) a clearly smaller Ca2+ -dependent inactivation (10%; P < 0.05), (4) L-type channels with 5 times slower activation and inactivation kinetics ( P < 0.05), and (5) slower kinetics of L-type channels that become faster and more similar to those in white-background adapted cells when the intracellular Ca2+ -buffering capacity is reduced. Furthermore, white-adapted melanotropes possess LVA-type Ca2+ channels, which are lacking from cells from black-adapted animals. The melanotrope calmodulin mRNA level does not differ between the two adaptation states. These results indicate that HVA L-type channel kinetics differ in relation to environmentally induced changes in cellular secretory state, probably mediated via intracellular Ca2+ -buffering, whereas the occurrence of LVA Ca2+ channels may depend on environmentally controlled channel gene expression.