Multiple calcium channels in synaptosomes: voltage dependence of 1,4-dihydropyridine binding and effects on function

Journal Article · Tue Jul 12 04:00:00 EDT 1988 · Biochemistry; (United States)

DOI:https://doi.org/10.1021/bi00414a049· OSTI ID:6829296

Dunn, S M.J.

The voltage dependence of binding of the calcium channel antagonist, (+)-(/sup 3/H)PN200-110, to rat brain synaptosomes and the effects of dihydropyridines on /sup 45/Ca/sup 2 +/ uptake have been investigated. Under nondepolarizing conditions (+)-(/sup 3/H)PN200-110 binds to a single class of sites with a K/sub d/ of 0.07 nM and a binding capacity of 182 fmol/mg of protein. When the synaptosomal membrane potential was dissipated either by osmotic lysis of the synaptosomes or by depolarization induced by raising the external K/sup +/ concentration, there was a decrease in affinity with no change in the number of sites. The effects of calcium channel ligands on /sup 45/Ca/sup 2 +/ uptake by synaptosomes have been measured as a function of external potassium concentration, i.e., membrane potential. Depolarization led to a rapid influx of /sup 45/Ca/sup 2 +/ whose magnitude was voltage-dependent. Verapamil almost completely inhibited calcium uptake at all potassium concentrations studies. In contrast, the effects of dihydropyridines (2 ..mu..M) appear to be voltage-sensitive. At relatively low levels of depolarization nitrendipine and PN200-110 completely inhibited /sup 45/Ca/sup 2 +/ influx, whereas the agonist Bay K8644 slightly potentiated the response. At higher K/sup +/ concentrations an additional dihydropyridine-insensitive component of calcium uptake was observed. These results provide evidence for the presence of dihydropyridine-sensitive calcium channels in synaptosomes which may be activated under conditions of partial depolarization.

• Research Organization: Univ. of Iowa, Iowa City (USA)
• OSTI ID: 6829296
• Journal Information: Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 27:14; ISSN BICHA
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
ALKALI METAL COMPOUNDS
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METAL COMPOUNDS
ANIMALS
AZINES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CALCIUM 45
CALCIUM COMPOUNDS
CALCIUM ISOTOPES
CATIONS
CELL CONSTITUENTS
CELL MEMBRANES
CHARGED PARTICLES
DAYS LIVING RADIOISOTOPES
ELECTRIC POTENTIAL
EVEN-ODD NUCLEI
HETEROCYCLIC COMPOUNDS
INTERMEDIATE MASS NUCLEI
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ISOTOPE APPLICATIONS
ISOTOPES
LABELLED COMPOUNDS
MAMMALS
MEMBRANES
NUCLEI
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
POTASSIUM COMPOUNDS
PYRIDINES
RADIOISOTOPES
RADIORECEPTOR ASSAY
RATS
RODENTS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
UPTAKE
VERTEBRATES