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Talk Abstract
Modeling Synchronized Calcium Oscillations in Pituitary Cells Coupled Through Gap Junctions

Yue-Xian Li
Departments of Mathematics and Zoology
University of British Columbia
Vancouver, B.C., Canada V6T 1Z2

The role of electrical activities in the endocrine cells of the pituitary gland remains obscure although most pituitary cells are known to possess mechanisms of generating action potentials (APs) like neurons. Hormone-secretion by pituitary cells is mainly controlled by stimulating/inhibiting factors released from the neuroendocrine cells in the hypothalamus. Thus, local coordination between neighboring pituitary cells has long been considered insignificant because it appears to be unnecessary if all cells respond to the same signal and are thus "synchcronized" whenever the signal is present. However, it is found recently that APs in neighboring pituitary cells can synchronize via gap-junctional coupling. This makes a review of the role of electrical coupling on local coordination between pituitary cells necessary. Now we know that pituitary cells do generate APs that can synchronize in neighboring cells. The question is what can such synchronized electrical activity bring about. This study attempts to give one answer to this question by modelling pituitary cells coupled through gap-junctions. In some pituitary cells such as gonadotrophs, Ca2+ entry during spontaneous membrane spiking does not contribute significantly to their secretory functions while agonist-induced, oscillatory Ca2+ release from intracellular stores plays the key role. Although the intracellular Ca2+ oscillators in neighboring cells do not talk to each other directly, they both interact with their respective plasma membranes via an activation-inhibition loop, i.e. APs generated by the plasma activates the intracellular oscillator while the latter inhibits the electrical activity of the membrane. Our model study shows that synchrony in APs can synchonize the intracellular Ca2+oscillators in neighboring cells. An interesting theoretical question also arises from this study, i.e. under what general conditions can oscillators coupled in an activation-inhibition loop phase-lock to each other? Some preliminary results will be discussed.

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1998-1999 Mathematics in Biology