Effects of hyposmotic stress on exocytosis in isolated turbot, Scophthalmus maximus, hepatocytes

Abstract

The effect of hyposmotic shock on exocytosis was examined in isolated hepatocytes of turbot, a marine flatfish, using the molecular probe FM1-43. Sudden exposure to a reduced osmolality caused an increase in cell exocytic activity related to the osmotic gradient between intra- and extracellular fluids. Cytoskeletal microtubules could contribute to this hyposmotic-induced exocytosis since colchicine inhibited the process. Protein kinase C, phosphatidylinositol-3 kinase, phospholipases A2, C and D could constitute key enzymes in the mechanism since their inhibition by specific agents altered the hyposmotic-induced exocytic activity. Moreover, arachidonic acid and derivates from the 5-lipoxygenase pathway as well as calcium could participate in the process. As regulatory volume decrease (RVD) exhibited by turbot hepatocytes following hyposmotic stimulation involves similar features, a potential role of exocytosis in volume regulation is suggested. In particular, exocytosis could serve RVD by contributing to ATP release since this latter process similarly appeared to be phospholipase D-dependent and related to the osmotic gradient. This study provides the first evidence of a volume-sensitive exocytosis that could aim at volume constancy in a marine teleost fish cell type.

Physiology of Cell Volume Regulation in Vertebrates

“…Nonetheless, channels regulated by membrane stretch exist in the eukaryotic plasma membrane and may be of importance after sudden, large changes in cell volume, or under con-ditions when cells have exhausted their membrane reservoirs, although this is a controversial issue (see below). The dramatic changes in endo-and exocytosis rates observed in osmotically perturbed cells (747,852,1024) could also be initiated at least in part via mechanical/ chemical changes in the lipid bilayer (see Ref. 322).…”

“…322). Third, cell shrinkage inhibits, and cell swelling stimulates, exocytosis (and vesicle recycling in general), in a manner which is, not surprisingly, dependent on the cytoskeleton (747,852,1024,1034). Changes in vesicle recycling may regulate the transporters/channels both through signaling events, exemplified by the vesicle recycling-dependent, swellinginduced release of ATP from intestine 407 cells (1024) and through plasma membrane insertion/retrieval of the transport proteins.…”

A microarray-based transcriptomic time-course of hyper- and hypo-osmotic stress signaling events in the euryhaline fishGillichthys mirabilis:osmosensors to effectors

“…Protein kinase C (PKC) is a major cell signaling intersection with an established role during osmotic stress, including promoting cell volume regulation during hypo-osmotic stress (Ollivier et al, 2006) and activating Na + /K + /Cl -co-transporters during hyperosmotic stress (Lionetto et al, 2002). During hypo-osmotic stress in G. mirabilis gill tissue, PKC Δ mRNA expression was downregulated 1.7-fold during the second hour of exposure (Fig.…”

Differential Gene Expression in Liver, Gill, and Olfactory Rosettes of Coho Salmon (Oncorhynchus kisutch) After Acclimation to Salinity

“…PKN1 is part of the protein kinase C (PKC) superfamily and is activated by Rho family small G proteins. PKC is involved in osmotic stress signaling and promotes volume regulation after hypo-osmotic stress (Ollivier et al 2006). During hyperosmotic stress, PKC has been shown to activate Na + /K + /Cl − co-transporter (Lionetto et al 2002).…”