Tarantula venom disrupts cells in unexpected way.

Cells regulate their internal environment using a sensitive network of membrane channels that control the flow of ions and water molecules into and out of the cells (SN: 10/18/03, p. 246). Two new studies published in the July 8 Nature claim that compounds in tarantula venom interfere with these channels in an unusual way.

Philip Gottlieb of the State University of New York, Buffalo and his colleagues investigated the action of one venom chemical on stretch-activated channels, which open and close in response to changes in a membrane's tension. Researchers had expected that the compound, a protein fragment, or peptide, bound to and closed the channel, which is normally open.

To test this model, the researchers synthesized a right-handed mirror image of the peptide and exposed cell membranes to it. Expecting the right-handed form to have no effect because its structure is slightly different from that of the natural form, the researchers observed that the right-handed peptide also inhibited the channels. Instead of doing so by attaching to each channel, however, the peptide slipped into and disrupted the membrane at spots near the channels. That caused the channel to lose its tension-sensing capacity, the scientists suspect.

In the second report, Roderick MacKinnon and Seok-Yong Lee of Rockefeller University in New York showed that another peptide from tarantula venom inhibits a different kind of channel in the same membrane-disrupting way.

Because ion channels are involved in cardiac arrhythmias and many diseases, such as muscular dystrophy, compounds that mimic the activity of these venom peptides could serve as potential drugs.--A.G.