INHIBITION OF NEURONAL CALCIUM CHANNELS BY A NOVEL PEPTIDE SPIDER TOXIN, DW13.3

Peptide toxins have proved to be useful agents, both in discriminating between different components of native calcium channel currents and i n the molecular isolation and designation of their cloned channel coun terparts. Here, we describe the isolation and characterization of the biochemical and physiological properties of a novel 74-amino acid pept ide toxin (DW13.3) extracted from the venom of the spider Filistata hi bernalis. The subtype specificity of DW13.3 was investigated using cal cium channel currents recorded from two separate expression systems an d several different cultured mammalian cell preparations. Overall, DW1 3.3 potently blocked all native calcium channel currents studied, with the exception of T-type currents recorded from GH3 cells. Examination of transiently expressed calcium channels in oocytes showed that DW13 .3 had the highest affinity for alpha 1A, followed by alpha 1B > alpha 1C > alpha 1E. The affinity of DW13.3 for alpha 1B N-type currents va ried by 10-fold between expressed channels and native currents. Althou gh block occurred in a similar 1:1 manner for all subtypes, DW13.3 pro duced a partial block of both alpha 1A currents and P-type currents in cerebellar Purkinje cells. Selective occlusion of the P/Q-type channe l ligand omega-conotoxin MVIIC (but not omega-agatoxin IVA) from its b inding site in Purkinje neurons suggests that DW13.3 binds to a site c lose to the pore of the channel. The inhibition of different subtypes of calcium channels by DW13.3 reflects a common ''macro'' binding site present on all calcium channels except T-type.