Exocytosis in Astrocytes: Transmitter Release and Membrane Signal Regulation

Abstract

Astrocytes, a type of glial cells in the brain, are eukaryotic cells, and a hallmark of these are subcellular organelles, such as secretory vesicles. In neurons vesicles play a key role in signaling. Upon a stimulus-an increase in cytosolic concentration of free Ca(2+) ([Ca(2+)](i))-the membrane of vesicle fuses with the presynaptic plasma membrane, allowing the exit of neurotransmitters into the extracellular space and their diffusion to the postsynaptic receptors. For decades it was thought that such vesicle-based mechanisms of gliotransmitter release were not present in astrocytes. However, in the last 30 years experimental evidence showed that astrocytes are endowed with mechanisms for vesicle- and non-vesicle-based gliotransmitter release mechanisms. The aim of this review is to focus on exocytosis, which may play a role in gliotransmission and also in other forms of cell-to-cell communication, such as the delivery of transporters, ion channels and antigen presenting molecules to the cell surface.

The uptake, retention and clearance of drug-loaded dendrimer nanoparticles in astrocytes – electrophysiological quantification

“…Astrocytes, like other eukaryotic cells, contain secretory vesicles with varied diameter and are suitable for vesicle luminal cargo release, as for the delivery of membrane-associated receptors to the plasma membrane. [45][46][47][48] Compared with neurons, the kinetics of exocytosis was shown to be slower in astrocytes 49 with several types of discrete vesicle interactions with the plasma membrane 24,50 as recorded in this study. The interaction of NPs with the plasma membrane and especially how NPs modify merging of the unitary vesicle with the plasma membrane have not been carried out but are important in relation to intracellular retention and possible clearance of NPs.…”

Excitable Astrocytes: Ca2+- and cAMP-Regulated Exocytosis

“…DCVs in cultured astrocytes contain the secretory proteins secretogranins II [34,65,103] and III [104]. Besides secretogranins, DCVs/less DCVs [28] in culture can also store chromogranins [42], ANP [19,65], neuropeptide Y (NPY) [103,105] and a fraction of cellular ATP [36,37]. DCVs containing secretogranins were recently reported in astrocytes in human brain tissue [42], confirming the existence of DCV vesicles also in situ.…”

“…In cultured astrocytes, several vesicular compartments were determined that may undergo regulated exocytosis, including clear electron-lucent small SLMVs; their morphology strongly resembles that of synaptic vesicles (SVs) of nerve terminals [21,68,71,79], dense core vesicles (DCVs)/less DCVs [34,96], and secretory lysosomes [24]. These vesicles may (co)store and release low and/or high molecular weight chemical messengers [28,96].…”

“…-dependent vesicle-based mechanism (i.e. exocytosis), by using a variety of experimental approaches, including optical methods, membrane capacitance measurements, electrochemical amperometry, as well as via selective interference with proteins of the exocytotic machinery [28,29]. The process of exocytosis, which may occur under physiologic conditions, involves the merger of gliosignal-containing vesicles with the plasma membrane.…”

Local electrostatic interactions determine the diameter of fusion pores

“…Astrocytes are electrically silent and abundant glial cells in the brain, which actively contribute to information processing in the central nervous system by releasing gliotransmitters. 37 In astrocytes, reversible discrete steps in C m were observed in controls with 2 mM Ca 2C ( Fig. 2A) and in conditions without Ca 2C (Fig.…”