Ultrastructure and permeability characteristics of the membranes of mucous granules of the hagfish

Defensive slime formation in Pacific hagfish requires Ca2+ and aquaporin mediated swelling of released mucin vesicles

“…This suggests that the two kinds of swelling can be traced to differences in the vesicle membranes. Luchtel et al (Luchtel et al, 1991) also proposed that vesicle rupture was mediated by the vesicle membrane, and suggested that it is permeable to monovalent anions and cations of all valencies, and that the movement of these ions into the vesicle causes osmotic influx of water. Given the high concentrations of Na + and Cl -in seawater, it is indeed likely that their concentration gradients would Lowercase letters indicate significant differences (P<0.05) among control treatments, and uppercase letters indicate significant differences (P<0.05) among solutions containing mercury.…”

“…Vesicles can be stabilized in concentrated (1 mol l −1 or higher) solutions containing polyvalent anions such as citrate, sulfate and phosphate, but appear to rupture in solutions containing monovalent anions, regardless of the valency of the associated cation (Luchtel et al, 1991;Salo et al, 1983). Based on these observations, Luchtel et al (Luchtel et al, 1991) hypothesized that ions from seawater enter the vesicle down their concentration gradients, resulting in an influx of water and the swelling and rupture of the vesicle.…”

“…In contrast to exocytotic release, in which mucin vesicles fuse with the apical plasma membrane of a mucous cell, holocrine release from hagfish slime glands results in the rapid and mass release of numerous mucin vesicles from many GMCs (Deyrup-Olsen and Luchtel, 1998). When the vesicles come into contact with seawater, they rapidly burst and the mucins interact with seawater and threads to produce slime (Luchtel et al, 1991).…”

“…The exudate combines with seawater to form slime, an effective defense mechanism because of its ability to lodge on gills and impair respiration (Lim et al, 2006;Zintzen et al, 2011). The exudate consists of two principal components, long (~up to 15 cm), thin (~1-3 μm wide) protein threads and mucin-like glycoproteins (Luchtel et al, 1991;Salo et al, 1983). Recent findings have demonstrated that during mixing of slime exudate with seawater, the mucins elongate into strands and assist in the unravelling of condensed slime threads .…”

“…Hagfish mucin vesicles are disc-shaped structures that are ~7 μm along the major axis, and are encased by a lipid bilayer (Luchtel et al, 1991). Vesicles can be stabilized in concentrated (1 mol l −1 or higher) solutions containing polyvalent anions such as citrate, sulfate and phosphate, but appear to rupture in solutions containing monovalent anions, regardless of the valency of the associated cation (Luchtel et al, 1991;Salo et al, 1983).…”