PRESYNAPTIC INHIBITION OF [H-3] NITRENDIPINE BINDING AND MODIFICATIONOF MEMBRANE-PROPERTIES BY INSECTICIDAL DIHYDROPYRAZOLES IN MAMMALIAN BRAIN

Citation
Ag. Zhang et Ra. Nicholson, PRESYNAPTIC INHIBITION OF [H-3] NITRENDIPINE BINDING AND MODIFICATIONOF MEMBRANE-PROPERTIES BY INSECTICIDAL DIHYDROPYRAZOLES IN MAMMALIAN BRAIN, Pesticide biochemistry and physiology, 55(3), 1996, pp. 200-209
Citations number
49
Categorie Soggetti
Biology,Physiology,Entomology
ISSN journal
00483575
Volume
55
Issue
3
Year of publication
1996
Pages
200 - 209
Database
ISI
SICI code
0048-3575(1996)55:3<200:PIO[NB>2.0.ZU;2-H
Abstract
RH-3421 and RH-5529 displace specifically bound [H-3]nitrendipine in m ouse brain synaptosomes, suggesting that dihydropyrazoles act at presy naptic L-type calcium channels in mammalian brain. Scatchard analysis revealed that both compounds interfere with binding of [H-3]nitrendipi ne through a mechanism which reduces the number of available radioliga nd binding sites (B-max) without altering the affinity (K-d) for remai ning sites. In addition, there was no discernible change in either the rate of association of [H-3]nitrendipine or in the rate of radioligan d dissociation when the binding preparation was exposed to dihydropyra zoles, Such a binding profile indicates that dihydropyrazoles operate as noncompetitive blockers of [H-3]nitrendipine binding without allost eric involvement. The effects of RH-3421 and RH-5529 on the physical p roperties of synaptic plasma membranes prepared from mouse brain were also evaluated using the fluorescence probes 1,6-diphenyl-1,3,5-hexatr iene (DPH) and 1-(4-trimethyl-ammonium phenyl)-6-phenyl-1,3,5-hexatrie ne (TMA-DPH), which monitor the physical state of lipids in the membra ne core and membrane surface, respectively. Exposure of synaptic membr anes to RH-3421 and RH-5529 resulted in a reduction in fluorescence po larization of both probes, confirming that these lipid domains are acc essible to dihydropyrazoles. Estimates of static and dynamic parameter s show that lipid order and fluidity are modified within surface and c ore regions by dihydropyrazoles; however, the changes to regions probe d by TMA-DPH appear more closely correlated with binding data. Overall , our results are consistent with the proposal that dihydropyrazoles r educe the availability of [H-3]nitrendipine binding sites, possibly by modifying the physicostructural properties of the surface membrane. H owever, we do not exclude the possibility that dihydropyrazoles are ir reversible inhibitors of [H-3]nitrendipine binding or cause more subtl e interference with regulatory biomolecules in the channel environment . (C) 1996 Academic Press