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

Journal Article · Tue Jul 12 00:00:00 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

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
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
IONS
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