Calcium dynamics in the secretory granules of neuroendocrine cells

Abstract

a b s t r a c t Cellular Ca 2+ signaling results from a complex interplay among a variety of Ca 2+ fluxes going across the plasma membrane and across the membranes of several organelles, together with the buffering effect of large numbers of Ca 2+ -binding sites distributed along the cell architecture. Endoplasmic and sarcoplasmic reticulum, mitochondria and even nucleus have all been involved in cellular Ca 2+ signaling, and the mechanisms for Ca 2+ uptake and release from these organelles are well known. In neuroendocrine cells, the secretory granules also constitute a very important Ca 2+ -storing organelle, and the possible role of the stored Ca 2+ as a trigger for secretion has attracted considerable attention. However, this possibility is frequently overlooked, and the main reason for that is that there is still considerable uncertainty on the main questions related with granular Ca 2+ dynamics, e.g., the free granular [Ca 2+ ], the physical state of the stored Ca 2+ or the mechanisms for Ca 2+ accumulation and release from the granules. This review will give a critical overview of the present state of knowledge and the main conflicting points on secretory granule Ca 2+ homeostasis in neuroendocrine cells.

An Intracellular Ammonium Transporter Is Necessary for Replication, Differentiation, and Resistance to Starvation and Osmotic Stress in Trypanosoma cruzi

“…We also evaluated starvation-induced autophagy in these cells by incubating them in PBS or LIT medium for 20 h. Immunofluorescence microscopy was done using antibodies against the autophagy marker Atg8.1, which is the ortholog of LC3-II in mammalian cells ( 14 ). TcAMT -KO cells had significantly increased numbers of autophagosomes per cell under starvation conditions (PBS incubation) ( Fig.…”

“…The cells were resuspended at a density of 1 × 10 7 /ml in PBS or LIT medium and left for 20 h at 28°C. For Western blot and qRT-PCR assays, aliquots were taken prior to and after incubation for 20 h. Expression of the TcATG8.1 autophagy marker and autophagosome formation in T. cruzi epimastigotes incubated in LIT medium or under starvation conditions was estimated by immunofluorescence analysis using anti-TcATG8.1 antibody as described previously ( 14 ).…”

Acidocalcisomes of Trypanosoma brucei have an inositol 1,4,5-trisphosphate receptor that is required for growth and infectivity

“…Secretory granules of chromaffin cells (40), pancreatic β-cells (41), acinar (42) cells, secretory granules of airway goblet cells (43), and mast cells (44) have been shown to possess IP 3 Rs, although some of these results have been disputed (as discussed in ref. 45). However, it is interesting to note that some of these secretory granules, such as the mast cells granules, have similarities with acidocalcisomes (46).…”

CRISPR/Cas9-mediated endogenous C-terminal Tagging of Trypanosoma cruzi Genes Reveals the Acidocalcisome Localization of the Inositol 1,4,5-Trisphosphate Receptor

“…IP 3 Rs can also be targeted to the plasma membrane, where they are important for Ca 2ϩ entry (26). Secretory granules of a variety of cells (27)(28)(29)(30)(31) were reported to possess IP 3 Rs, although this was challenged (32). An IP 3 R localizes to the contractile vacuole in Paramecium tetraurelia, as detected with specific antibodies (33).…”