Subcellular Calcium Transients Visualized by Confocal Microscopy in a Voltage-Clamped Vertebrate Neuron

Abstract

Confocal laser-scanned microscopy and long-wavelength calcium (Ca2+) indicators were combined to monitor both sustained and rapidly dissipating Ca2+ gradients in voltage-clamped sympathetic neurons isolated from the bullfrog. After a brief activation of voltage-dependent Ca2+ channels, Ca2+ spreads inwardly, and reaches the center of these spherical cells in about 300 milliseconds. Although the Ca2+ redistribution in the bulk of the cytosol could be accounted for with a radial diffusion model, local nonlinearities, suggesting either nonuniform Ca2+ entry or spatial buffering, could be seen. After electrical stimulation, Ca2+ signals in the nucleus were consistently larger and decayed more slowly than those in the cytosol. A similar behavior was observed when release of intracellular Ca2+ was induced by caffeine, suggesting that in both cases large responses originate from Ca2+ release sites near or within the nucleus. These results are consistent with an amplification mechanism involving Ca2(+)-induced Ca2+ release, which could be relevant to activity-dependent, Ca2(+)-regulated nuclear events.

All-or-None Ca2+Release from Intracellular Stores Triggered by Ca2+Influx through Voltage-Gated Ca2+Channels in Rat Sensory Neurons

“…This provided an easily discerned temporal separation of the portion of the increase in [Ca 2ϩ ] i produced by influx from that contributed by release (Fig. 2C) this study, however, the increase would not be predicted to exceed 500 msec (Hernandez-Cruz et al, 1990;Blumenfeld et al, 1992). efflux.…”

“…(Hernandez-Cruz et al, 1990;Blumenfeld et al, 1992), followed by diffusion toward the center of the soma. Powerful buffering, sequestration, and efflux processes (Miller, 1991;Werth et al, 1996) severely restrict the distance that Ca 2ϩ signals will travel.…”

Cytosolic organelles shape calcium signals and exo–endocytotic responses of chromaffin cells

“…These HCMDs can reach concentrations as high as 10-100 M [7,182] Because of rapid diffusion of Ca 2+ towards the surrounding cytosol, the HCMDs are highly restricted in time and space [7,183]. The presence of mobile calcium buffers accelerates diffusion and opposes the development of HCMDs [180,[184][185][186]; for example, at concentrations of 50 M, fura-2 increases the apparent rate of Ca 2+ diffusion four times [180].…”

Caffeine causes glycerophosphorylcholine accumulation through ryanodine-inhibitable increase of cellular calcium and activation of phospholipase A2 in cultured MDCK cells

“…The following studies were aimed at defining which of the many pathways of caffeine action is involved. (Slivka and Insel, 1987;Gronich et al, 1990;Nakamura et al, 1991;Weiss and Insel, 1991), and millimolar concentrations of caffeine may increase [Ca 2 + ] i c o n c e n t r a t i o n both in muscular (Fleischer et al, 1985;Campbell et al, 1987;Iino et al, 1988) and non-muscular cells (Lipscombe et al ., 1988;Burgoyne et al ., 1989;Hernandez-Cruz et al, 1990;Malgaroli et al, 1990;Zacchetti et al, 1991). Caffeine mobilizes cellular Ca 2+ from intracellular stores by activating Ca 2 + channels that are sensitive to ryanodine.…”

“…It is well known that in a variety of cell types such as muscular cells (Fleischer et al, 1985;Campbell et al , 1987;Iino et al, 1988), neurons (Lipscombe et al, 1988;Hernandez-Cruz et al, 1990;Zacchetti et al, 1991), endocrine cells (Burgoyne et al, 1989;Malgaroli et al, 1990) and the pancreatic acinar cells (Wakui et al, 1990), caffeine increases the intracellular free calcium ([Ca 2+ ] i ) level through ryanodine, a neutral plant alkaloid, -sensitive or -insensitive Ca 2 + channel located in intracellular calcium stores. However, there is no informations about the action of caffeine and ryanodine on the cellular calcium change in renal epithelial cells.…”