Minimal Model for Intracellular Calcium Oscillations and Electrical Bursting in Melanotrope Calles of Xenopus Laevis.

MATHEMATICAL models; CALCIUM; NEUROENDOCRINE cells; XENOPUS laevis

A minimal model is presented to explain changes in frequency, shape, and amplitude of Ca[sup 2+] oscillations in the neuroendocrine melanotrope cell of Xenopus Laevis. It describes the cell as a plasma membrane oscillator with influx of extracellular Ca[sup 2+] via voltage-gated Ca[sup 2+] channels in the plasma membrane. The Ca[sup 2+] oscillations in the Xenopus melanotrope show specific features that cannot be explained by previous models for electrically bursting cells using one set of parameters. The model assumes a K[sub Ca]-channel with slow Ca[sup 2+]-dependent gating kinetics that initiates and terminates the bursts. The slow kinetics of this channel cause an activation of the K[sub Ca]-channel with a phase shift relative to the intracellular Ca[sup 2+] concentration. The phase shift, together with the presence of a Na[sup +] channel that has a lower threshold than the Ca[sup 2+] channel, generate the characteristic features of the Ca[sup 2+] oscillations in the Xenopus melanotrope cell. [ABSTRACT FROM AUTHOR]

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