Okadaic acid enhances neurotransmitter release at botulinum toxin (BoTx-A) poisoned mouse motor nerve terminals (MNTs)

DEPETRIS, RS, URBANO, FJ (COMPILADOR), & UCHITEL, OD.

Córdoba, Argentina.

Taller; III Taller de Neurociencias.; 2001

L-type voltage dependent calcium channels (VDCC) are coupled to nerve evoked neurotransmitter release during functional recovery of BoTx-A poisoned MNTs(§). However, the mechanisms responsible for this coupling and its modulation are yet unknown. Considering this, here we study whether the coupling to neurotransmitter release of these channels could be modulated by serine/threonine phosphorylation. BoTx-A was injected subcutaneously onto Levator auris longus muscle and quantal content was estimated by the failure method. We tested the effect of okadaic acid (OA), a specific serine/threonine phosphatase inhibitor, on L-type VDCC mediated neurotransmitter release (i.e., after MNTs preincubation with P/Q- and N-type VDCC blockers w-Agatoxin IVA 120nM and w-conotoxin GVIA 1µM). From 2 to 4 weeks after the application of BoTx-A, quantal content was increased by 1 µM OA (P<0.001). However, from 5 to 7 weeks no neurotransmitter release by L-type VDCC was observed and the application of OA was ineffective. This OA-induced increment in quantal content was reduced by Calciseptine 300 nM (>80% of reduction, P<0.01) suggesting that OA-action involved L-type VDCC. Therefore, these results suggest that from 2 to 4 weeks after the application of BoTx-A, neurotransmitter release is enhanced by serine/threonine phosphorylation through the modulation of L-type VDCC. (§) Santafe, Urbano, Lanuza & Uchitel. Neuroscience 95(2000): 227–34. Supported by: Univ. Buenos Aires (TW29), CONICET (PIP 4631/96) and SCYT-ANPCYT (PICT 97/1848). Dr. F.J. Urbano was a CONICET postdoctoral fellow.