Minimal model for intracellular calcium oscillations and electrical bursting in melanotrope cells of Xenopus laevis

A minimal model is presented to explain changes in frequency, shape, and am plitude of Ca2+ oscillations in the neuroendocrine melanotrope cell of Xeno pus Laevis. It describes the cell as a plasma membrane oscillator with infl ux of extracellular Ca2+ via voltage-gated Ca2+ channels in the plasma memb rane. The Ca2+ oscillations in the Xenopus melanotrope show specific featur es that cannot be explained by previous models for electrically bursting ce lls using one set of parameters. The model assumes a K-Ca-channel with slow Ca2+-dependent gating kinetics that initiates and terminates the bursts. T he slow kinetics of this channel cause an activation of the K-Ca-channel wi th a phase shift relative to the intracellular Ca2+ concentration. The phas e shift, together with the presence of a Na+ channel that has a lower thres hold than the Ca2+ channel, generate the characteristic features of the Ca2 + oscillations in the Xenopus melanotrope cell.