Intracellular calcium buffering shapes calcium oscillations in Xenopus melanotropes

Pflügers Archiv - Tập 443 - Trang 250-256 - 2001
W. Koopman1, W. Scheenen1, L. Schoolderman2, P. Cruijsen2, E. Roubos1, B. Jenks1
1Department of Cellular Animal Physiology, Institute of Cellular Signalling, University of Nijmegen, Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
2Department of Cellular Animal Physiology, Nijmegen Institute for Neurosciences, University of Nijmegen, Nijmegen, The Netherlands

Tóm tắt

The pituitary melanotrope cell of Xenopus laevis displays cytosolic Ca2+ oscillations that arise for the interplay between the burst-like openings of voltage-operated Ca2+ channels and Ca2+-extrusion mechanisms. We have previously shown that Ca2+-extrusion rates increase with increases in [Ca2+]i, suggesting that Ca2+ itself plays a role in shaping the Ca2+ oscillations. The purpose of the present study was to test this hypothesis by manipulating the intracellular Ca2+ buffering capacity of the cell and determining the consequences of such manipulations for the shape of the Ca2+ oscillations. We manipulated the cytosolic buffering capacity by loading the fast Ca2+ chelator BAPTA into cells. During loading the [Ca2+]i was dynamically imaged with confocal laser scanning microscopy. The basal [Ca2+]i was reduced with BAPTA loading and this reduction was associated with lower Ca2+-extrusion rates, a broadening of the Ca2+ oscillations and declined oscillation frequencies. Short loading periods of the buffer led to new, stable patterns of Ca2+ signaling and to reduced but stable levels of peptide secretion. We propose that the cytosolic Ca2+ buffer capacity, and thus by inference the profile of intracellular Ca2+ buffering proteins, is an important factor in setting the frequency and shape of Ca2+ oscillations.