Cometary magnitude distribution and the fading of comets

Cytotoxicity of equinatoxin II from the sea anemone Actinia equina involves ion channel formation and an increase in intracellular calcium activity

Equinatoxin II is a 20-kDa basic protein isolated from the sea anemone Actinia equina. The aim of our work was to investigate the primary molecular basis for the cytotoxic effects of equinatoxin II in two model systems: single bovine lactotrophs and planar lipid bilayers. Previous work has shown that equinatoxin II produces rapid changes in cell morphology, which are dependent on external calcium. It has also been reported that addition of equinatoxin II increases membrane electrical conductance, which suggests that the cytotoxic action of equinatoxin II involves an increase in the permeability of membranes to Ca2+. Extensive changes in cytosolic Ca2+ activity are thought to invoke irreversible changes in cell physiology and morphology. In this paper, we show that morphological changes brought about by equinatoxin II in bovine lactotrophs are associated with a rapid rise in cytosolic Ca2+ activity, monitored with a fura-2 video imaging apparatus. Moreover, incorporation of equinatoxin II into planar lipid bilayers produces Ca2+ permeable ion channels. This suggests that the mode of equinatoxin II cytotoxicity involves the formation of cation (Ca2+) permeable channels in cell membranes.

Secretin-regulated chloride channel on the apical plasma membrane of pancreatic duct cells

Using the patch clamp technique we have identified a small conductance ion channel that typically occurs in clusters on the apical plasma membrane of pancreatic duct cells. The cell-attached current/voltage (I/V) relationship was linear and gave a single channel conductance of about 4 pS. Since the reversal potential was close to the resting membrane potential of the cell, and unaffected by changing from Na+-rich to K+-rich pipette solutions, the channel selects for anions over cations in cell-attached patches. The open state probability was not voltage-dependent. Adding 25 mM-bicarbonate to the bath solution caused a slight outward rectification of the I/V relationship, but otherwise, the characteristics of the channel were unaffected. In excised, inside-out, patches the I/V relationship was linear and gave a single channel conductance of about 4 pS. A threefold chloride concentration gradient across the patch (sulphate replacement) shifted the single channel current reversal potential by -26 mV, indicating that the channel is chloride selective. Stimulation of duct cells with secretin (10 nM), dibutyryl cyclic AMP (1 mM) and forskolin (1 microM) increased channel open state probability and also increased the number of channels, and/or caused disaggregation of channel clusters, in the apical plasma membrane. Coupling of this channel to a chloride/bicarbonate exchanger would provide a mechanism for electrogenic bicarbonate secretion by pancreatic duct cells.