FUNCTIONAL DIVERSITY OF TOXINS FROM SPIDERS OF THE GENUS Phoneutria

CAMPOS F.V. (1), LÚCIO A.D. (1), MATAVEL A. (1), LEÃO R.M. (1), KUSHMERICK C. (1), CRUZ J.S. (1), CORDEIRO M.N. (2), RICHARDSON M. (2), DINIZ C.R. (1,2) AND BEIRÃO P.S.L. (1)

(1) Department of Biochemistry and Immunology, ICB-UFMG, Belo Horizonte, MG; (2) Fundação Ezequiel Dias, Belo Horizonte, MG, Brazil

Spiders of the genus Phoneutria are prevalent over wide areas of Brazil, and their venoms contain a rich variety of peptides, most with activities on ion channels. After the pioneering work of Dr. C. R. Diniz, a number of investigators have been engaged in the determination of the structural and functional diversity of toxins contained in the venom of the spider Phoneutria nigriventer. Five fractions of polypetide toxins (mw. 3.5-8.5 kDa) have been described in this venom, including an insect-specific toxin. More recently, a small (4 kDa) family of neurotoxins has been identified in three species of the same genus: Phoneutria nigriventer, Phoneutria reidyi and Phoneutria keyserlingi. Preliminary work suggested that these toxins act on ion channels. We have focused our interest in the mechanism of action of the toxins, by determining the channels they target and their mechanisms of action. We have used the patch clamp technique, in the whole cell configuration, and appropriate cell types to directly measure currents carried through Na, Ca and K channels, and have used biophysical and pharmacological markers to identify the subtypes of channels that were affected. Most of the toxins found in the fraction PhTx2 have strong inhibitory effect on Na channel inactivation. This effect can account for the prevailing excitatory effect of the crude venom. In contrast, fraction PhTx3 is more diverse, containing toxins that inhibit Ca channels (w-PnTx3-3) and A-type K channels (PnTx3-1). Toxins that belong to the 4 kDa family inhibit L-type Ca channels, with different efficacies (PRTx27C3>PNTx27C4PNTx26An0C3, toxin PKTx32C4 having no effect). Since the overall inhibition of Ca channels is frequency-dependent, we propose that PhTx2 toxins potentiate the effect of PhTx3 fraction.

KEY WORDS: spider venom, neurotoxin, peptide, ion channel

FINANCIAL SUPPORT: CNPq and FAPEMIG

CORRESPONDENCE TO: PAULO BEIRÃO, Depto. Bioquímica ICB-UFMG. Phone: 55 31 3499-2663 / Fax: 55 31 3499-2614; email: pslb@ufmg.br