Characterization oc Ca2+-channels responsible for K+-evoked [H-3]noradrenaline release from rat brain cortex synaptosomes and their response to amyotrophic lateral sclerosis IgGs

The contribution of the different Ca2+-channel subtypes to the K+-evoked [H -3]noradrenaline release from rat cerebral cortex synaptosomes has been inv estigated. In the same experimental model, it was also verified whether the calcium-mediated neurotransmitter release is influenced by IgGs purified f rom sera of seven patients affected by sporadic amyotrophic lateral scleros is. Synaptosome treatment with 3.0 mu M nifedipine or 2.0 mu M calciseptine , which block L-type channels, slightly decreased [H-3]noradrenaline releas e, the reduction being 7 and 13% of the control values, respectively. The b lockade of N-type Ca2+-channels with omega-conotoxin-GVIA (0.001-1.0 mu M) induced a concentration-dependent reduction of the neurotransmitter release , with maximum effect of 34%. omega-Agatoxin-IVA failed to significantly af fect the studied release, which was instead markedly reduced by omega-conot oxin-MVIIC. After the blockade of N-type channels with maximal concentratio ns of omega-conotoxin-GVIA, 3.0 mu M omega-conotoxin-MVIIC reduced the rele ase by 58%. Synaptosome treatment with amyotrophic lateral sclerosis IgGs e nhanced the K+-evoked [H-3]noradrenaline release, which was mostly mediated by P/Q- and N-type Ca2+-channels. The increase induced by pathologic IgGs (0.2 mg/ml) ranged from 11 to 62% for the different patients, and it was co ncentration-dependent. The basal release was instead unaffected by IgG trea tment. The results of the present study suggest that the K+-evoked [H-3]nor adrenaline release from brain cortex synaptosomes is mainly mediated by act ivation of P/Q- and N-type Ca2+-channels. Autoantibodies present in the ser a of patients affected by sporadic amyotrophic lateral sclerosis may intera ct with these channels by producing an increased calcium influx, with conse quent enhancement of the neurotransmitter release. Preliminary results of t he present study have been published in abstract form (Martire et al., 1997 , Pharmacol. Res. 35:9). (C) 1999 Academic Press.