Spatial Distribution of Ca2+ Signals during Repetitive Depolarizing Stimuli in Adrenal Chromaffin Cells

Abstract

Exocytosis in adrenal chromaffin cells is strongly influenced by the pattern of stimulation. To understand the dynamic and spatial properties of the underlying Ca(2+) signal, we used pulsed laser Ca(2+) imaging to capture Ca(2+) gradients during stimulation by single and repetitive depolarizing stimuli. Short single pulses (10-100 ms) lead to the development of submembrane Ca(2+) gradients, as previously described (F. D. Marengo and J. R. Monck, 2000, Biophysical Journal, 79:1800-1820). Repetitive stimulation with trains of multiple pulses (50 ms each, 2Hz) produce a pattern of intracellular Ca(2+) increase that progressively changes from the typical Ca(2+) gradient seen after a single pulse to a Ca(2+) increase throughout the cell that peaks at values 3-4 times higher than the maximum values obtained at the end of single pulses. After seven or more pulses, the fluorescence increase was typically larger in the interior of the cell than in the submembrane region. The pattern of Ca(2+) gradient was not modified by inhibitors of Ca(2+)-induced Ca(2+) release (ryanodine), inhibitors of IP(3)-induced Ca(2+) release (xestospongin), or treatments designed to deplete intracellular Ca(2+) stores (thapsigargin). However, we found that the large fluorescence increase in the cell interior spatially colocalized with the nucleus. These results can be simulated using mathematical models of Ca(2+) redistribution in which the nucleus takes up Ca(2+) by active or passive transport mechanisms. These results show that chromaffin cells can respond to depolarizing stimuli with different dynamic Ca(2+) signals in the submembrane space, the cytosol, and the nucleus.

Dual role of calbindin‐D28K in vesicular catecholamine release from mouse chromaffin cells

“…6b). These measurements confirmed the presence of depolarization‐evoked Ca 2+ gradients as previously described for chromaffin cells (Marengo and Monck 2000, 2003). However, these measurements did not reveal differences in the depolarization‐evoked cytosolic Ca 2+ transients in WT and KO cells (Fig.…”

“…Figure 6(b and c) demonstrates that it was possible to discriminate between submembrane and cytosolic Ca 2+ dynamics, as shown previously (Marengo and Monck 2000, 2003). The increase in the submembrane Ca 2+ concentration is slightly faster than in the cytosol in both WT and KO chromaffin cells.…”

How the stimulus defines the dynamics of vesicle pool recruitment, fusion mode, and vesicle recycling in neuroendocrine cells

“…; Sorensen ). In this regard, high‐frequency stimulation of chromaffin cells provokes an important global Ca 2+ increase (Klingauf and Neher ; Marengo and Monck ; Fulop and Smith ), which triggers exocytosis of secretory vesicles irrespectively of their location and mobilizes vesicles from upstream to downstream pools (Voets et al . ; Marengo ).…”

“…). The intense stimulation of chromaffin cells provokes an important global Ca 2+ increase (Klingauf and Neher ; Marengo and Monck ; Fulop and Smith ), promoting exocytosis irrespective of the secretory vesicle location, mobilizing vesicles from upstream to downstream pools (Voets et al . ; Marengo ), and triggering the release of the totality of the transmitters stored in the chromaffin granules (Elhamdani et al .…”

“…Under basal conditions the action potential (AP) firing rate of chromaffin cells is low, approximately 0.2-0.5 Hz, while under stress the system approaches 10-20 Hz (Brandt et al 1976;Holman et al 1994;Fulop et al 2005). The intense stimulation of chromaffin cells provokes an important global Ca 2+ increase (Klingauf and Neher 1997;Marengo and Monck 2003;Fulop and Smith 2006), promoting exocytosis irrespective of the secretory vesicle location, mobilizing vesicles from upstream to downstream pools (Voets et al 1999;Marengo 2005), and triggering the release of the totality of the transmitters stored in the chromaffin granules (Elhamdani et al 2001;Fulop et al 2005). On the other hand, in rest conditions the firing frequency is low, Ca 2+ does not markedly accumulate (Fulop and Smith 2006), and therefore exocytosis would be limited to a group of vesicles that is closely coupled to VDCCs (Voets et al 1999;Marengo 2005;Or e and Artalejo 2005;Alvarez et al 2008).…”