(full paper is archived in the Miller Library)
Title: Novel effects of Conus californicus venom on voltage-gated potassium channels
Student Author(s): Etchebarne, Brett E.
Faculty Advisor(s): Gilly, William
Location: Final Papers Biology 175H
Date: June 1999
Abstract: Cone snails are predatory marine gastropods of the genus Conus which proliferated to over 500 species worldwide largely through the use of novel peptide toxins (conotoxins) that are injected into prey items through a harpooning apparatus. Conotoxins have evolved for maximal effect on prey species hunted by each cone snail species (Duda and Palumbi, 1999). All cone snail venoms examined thus far contain peptides that act with great specificity on a variety of channels including K+, Na+, Ca2+, and ACh receptors (Olivera et al, 1999). Conus californicus is indigenous to the California coastline. Venom samples were collected by extruding the contents of one venom duct into 0.5 ml external recording solution and were further diluted during experiments. Voltage-depenent K+ currents were recorded from Shaker B K+ channels, in which both N- and C-type inactivation were eleminated, using the whole-cell patch-clamp technique. When applied to the bathing solution, the venom was found to induce rapid inactivation of Ik.K+ current was reduced in a time- and concentration-dependent manner that fits satisfactorily with a simple model of open-channel block that applies to tertiary amines and quarternary ammonium (QA) that block K+channels at the inner mouth of the channel, but only after the channel has opened following a voltage step. Several lines of evidence are consistent with the venom acting on the external side of the membrane. First, the venom interacts with externally applied tetraethylammonium (TEA). an impermeant QA. An internal blocker would be expected to to be unaffected by external TEA. Second, recovery from venom-induced Ik block is similar to that from QA-block in its dependence on voltage, but different from QA in that recovery shows no acceleration in solutions with elevated external K= concentration. Lack of this effect suggests that the venom component in question is not acting to block internally, because it cannot be dislodged by inward Ik negative voltages. Third, channel-blocking action was preserved following dialysis of the venom at a 3500-molecular weight cut off. This suggests a large molecule such as a peptide is the active component.