An Electrophysiological Study On The Effects Of MiDCA1 (A PLA2) From The Venom Of Micrurus dumerilii carinicauda

^{1Dal Belo, C.A}.**, ¹Randazzo-Moura, P., ²Toyama, M.H.**, ²Marangoni, S., ¹Fontana, M.D., ³Rowan, E. G. ⁴Southan, A .¹Hyslop, S., ¹Rodrigues-Simioni, L.

1 Dept. de Farmacologia, FCM and 2 Dept. de Bioquímica, UNICAMP Campinas, SP, Brasil; 3 Dept. of Physiology and Pharmacology, University of Strathclyde, Glasgow-G4 0NR, U.K. 4 Ionix Pharmaceuticals Ltd., 418 Cambridge Science Park, Cambridge, CB4 0PA, U.K.

To investigate the site and mechanism of action of a novel PLA2 named MiDCA1 in mouse neuromuscular preparations. Adult male Swiss white mice (28-30g) were used. After anaesthesia (cloral hydrate, 300 mg/kg, i.p.) the hemidiaphragms and sciatic nerve were take out and mounted (Dal Belo et al., Toxicon, 2004, in press). Miniature end-plate potentials (MEPPs), end-plate potentials (EPPs) and resting potentials (RP) were measured in phrenic nerve-diaphragm preparations by conventional microelectrode techniques. Extracellular recording techniques were used to record action potentials events (CAPs) from sciatic nerves. Preparations were kept in aerated (95%O2 - 5%CO2) Tyrode solution (pH 7.4, 37°C) ,composition in (mM): NaCl 137, KCl 2.7, CaCl2 1.8, MgCl2 0.49, NaH2PO4 0.42, NaHCO3 11.9 and glucose 11.1. Whole-cell patch-clamp recordings were made using electrodes with a resistence of 3-6 MW (Hamill et al., 1981) in DRG neurons.  MiDCA1(2.4 µM) increased quantal content of EPPs to 386 ± 12% of control after 10 min, (n=14; p<0.05) and caused a triphasic change in the frequency of MEPPs (n=3, p<0.05). MiDCA1 (0.6 µM) also increased the amplitude of CAPs (30 ± 9%, n=3, p<0.05). Similar increase (29 ± 1%) were seen when 3,4-DAP (10 µM) was used (p<0.05, n=3). ).  Potassium currents elicited in freshly dissociated dorsal root glanglia neurones were blocked by 31 ± 1% (p<0.05) in the presence of 2.4 µM MiDCA1, whereas there was no effect on sodium currents. MiDCA1 is a new presynaptic PLA2 that interfere with neurotransmitter release probably by blocking nerve-terminal potassium channels.

Support : FAPESP

Correspondence to: priscilarandazzo@yahoo.com.br