Published in:
Journal of Neurochemistry, 72 (1999) 2, Seite 800-807
Language:
English
DOI:
10.1046/j.1471-4159.1999.0720800.x
ISSN:
0022-3042;
1471-4159
Origination:
Footnote:
Description:
Abstract : Effects of selective Ca2+ channel blockers onGABAergic inhibitory postsynaptic currents (IPSCs) were studied in the acutelydissociated rat nucleus basalis of Meynert (nBM) neurons attached with nerveendings, namely, the “synaptic bouton” preparation, and in thethin slices of nBM, using nystatin perforated and conventional whole‐cellpatch recording modes, respectively. In the synaptic bouton preparation,nicardipine (3 × 10‐6M) and ω‐conotoxin‐MVIIC(3 × 10‐6M) reduced the frequency of spontaneouspostsynaptic currents by 37 and 22%, respectively, whereasω‐conotoxin‐GVIA had no effect. After blockade of L‐ and P/Q‐typeCa2+ channels, successive removal of Ca2+ from externalsolution had no significant effect on the residual spontaneous activities,indicating that N‐, R‐, and T‐type Ca2+ channels are not involvedin the spontaneous GABA release. Thapsigargin, but not ryanodine, increasedthe frequency of spontaneous IPSCs in both the synaptic bouton and slicepreparations, suggesting the partial contribution of the intracellularCa2+ storage site to the spontaneous GABA release. In contrast,ω‐conotoxin‐GVIA (3 × 10‐6M) andω‐conotoxin‐MVIIC (3 × 10‐6M) suppressed theevoked IPSCs by 31 and 37%, respectively, but nicardipine produced nosignificant effect. The residual evoked currents were abolished inCa2+‐free external solution but not in the external solutioncontaining 10‐5M Ni2+, suggesting theinvolvement of N‐, P/Q‐, and R‐type Ca2+ channels but not L‐ andT‐type ones in the evoked IPSCs. Neither thapsigargin nor ryanodine had anysignificant effects on the evoked IPSCs. It was concluded that Ca2+ channel subtypes responsible for spontaneous transmitter release are different from those mediating the transmitter release evoked by nerve stimulation.