Intracellular calcium buffering shapes calcium oscillations in Xenopus melanotropes

Abstract

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.

Cysteinyl leukotriene 2 receptor‐mediated vascular permeability via transendothelial vesicle transport

“…The fact that BAPTA blocked vascular permeability but only marginally influenced the number of CysLT‐stimulated FITC‐albumin accumulation sites (Fig. 5) reveals that the Ca 2+ ‐buffering capacity of BAPTA is important for setting weaker oscillating Ca 2+ signals, as described previously in Xenopus melanotropes (22), which might influence exocytosis of labeled‐albumin from the vascular endothelial cells into the extravascular space.…”

The intracellular dissipation of cytosolic calcium following glucose re‐addition to carbohydrate depleted Saccharomyces cerevisiae

“…Cytosolic calcium buffering has been described in various mammalian cells to bind 90–99.9% of the total cytosolic calcium, leaving only 0.1–10% free depending on the cell type [34]. The large amount of calcium buffering proteins not only protect cells from calcium toxicity, but may also be involved in setting parameters of intracellular Ca 2+ signaling [35]. The importance of intracellular pH for calcium handling in the cytoplasm has been demonstrated [36].…”

Calcium Efflux Systems in Stress Signaling and Adaptation in Plants

“…Intracellular Ca 2+ buffering is an important determinant of the Ca 2+ signal specificity, as both the magnitude and kinetics of Ca 2+ signatures are critically dependent on Ca 2+ buffering (Lew et al, 1984; Koopman et al, 2001). At the same time, there appears to be no correlation between cytosol buffering capacity and steady-state free Ca 2+ level (Rizzuto and Pozzan, 2006).…”