Characterization of the Dihydropyridine Binding Sites of Rat Neocortical Synaptosomes and Microvessels

Abstract

The dihydropyridine binding sites associated with rat neocortical synaptosomes and microvessels were compared using an in vitro [3H]PN 200-110 [(+)-[methyl-3H]-isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5- methoxycarbonylpyridine-3-carboxylate] binding assay. Saturation experiments yielded similar KD values (approximately 70 pM) and Bmax values (approximately 400 fmol/mg of protein) for the two membrane preparations. Interaction experiments with [3H]PN 200-110 and various calcium-modulating substances provided further evidence for the practically identical nature of the synaptosomal and microvascular dihydropyridine binding sites. These findings predict that lipophilic dihydropyridines, simultaneously occupying the two central binding sites, have the dual effect of altering neuronal function and local blood flow.

Stimulation of Muscarinic Acetylcholine Receptors Increases Synaptosomal Free Calcium Concentration by Protein Kinase‐Dependent Opening of L‐Type Calcium Channels

“…The increase in [Ca2+Ii in synaptosomes treated with PKC-stimulating phorbol esters also is inhibited by DHP channel blockers (Adamson et al, 1989). Furthermore, binding sites for dihydropyridines have been characterised on synaptosomes (Dooley et al, 1987), and the a2 subunit of the DHP receptor has been identified in rat brain synaptosomes using polyclonal antibodies (Sharp and Campbell, 1989).…”

Formation of cerebrovascular anomalies in the ageing rat is delayed by chronic nimodipine application

“…Dihydropyridine (dhp) binding sites on cerebral microvessels have similar, if not identical, pharmacological properties to neuronal dhp binding sites [3]. Nimodipine exerts a vasodilatory action by a blockade of vascular L-type calcium channels, hereby increasing cerebral blood flow [13], known to be impaired during ageing [6].…”

Polyamines and Ca2+ Mediate Hyperosmolal Opening of the Blood‐Brain Barrier: In Vitro Studies in Isolated Rat Cerebral Capillaries

“…Our experiments have indicated that entry of extracellular Ca2+ through a verapamil-and nisolclipinesensitive pathway, presumably voltage-sensitive Ca2+ channels, is a prerequisite for the 1 M mannitcsl-mediated stimulation of ODC activity and the concomitant increase in 45Ca2+ influx, HRP uptake, and DG uptake. Brain microvessel membranes possess voltagesensitive Ca2+ channels, as identified by high-affinity dihydropyridine binding sites, that are identical to those present in neocortical synaptosomal membranes (Dooley et al, 1987). Extracellular Ca2+ is required for the induction of ODC activity in cultured cells by a number of agonists.…”