A peptide toxin blocking T-type calcium channels

Voltage-gated calcium channels mediate the entry of calcium ions along an electrochemical gradient into the cell. Within the cell calcium ions are key second messengers for controlling important physiological processes. Low voltage-gated T-type calcium channels are the main object of the submitted scientific proposal. The distribution of these channels in a wide variety of cell types and the low voltage of activation suggest that they are important in the regulation of cell calcium and electrical spiking activity. They are thought to play a role in smooth muscle contraction, aldosterone secretion, pacemaker activity in heart, fertilization, neuronal burst firing and insulin secretion. T-type currents are mainly detected at early stages of development and there is a growing evidence that they may also play an important role in regulation of the cell cycle, cell differentiation and fusion. Genetic abnormalities in expression of T-type channels have been proposed for several diseases. Therefore these ion channels appear as attractive new targets for the development of drugs. Venoms produced by many animals like scorpions, spiders, sea anemones, snakes and bees are rich sources of peptide toxins that interact remarkably selective with voltage-gated calcium channels. These tools have been used for biochemical and pharmacological characterization of different calcium channel types. The fact that no selective T-type calcium channel blockers have been discovered to date still impairs the characterization of this family of calcium channels. It is the aim of the submitted proposal to develop a useful selective T-type channel blocker. We isolated a novel peptide toxin from the venom of a spider. This toxin inhibits T-type calcium channels by modulating channel activation. During the course of the next year I will (1) map the binding site of the toxin on the channel (2) test the toxin`s activity on different other calcium channel types and splice variants (3) express the recombinant toxin in E.coli. Iodination of the toxin will yield a specific radioligand useful for radioligand binding studies. Mutant toxin will yield higher selectivity and affinity for T-type channels.