Binding of ( sup 125 I)iodipine to parathyroid cell membranes: Evidence of a dihydropyridine-sensitive calcium channel

Journal Article · Sun Apr 01 04:00:00 EDT 1990 · Endocrinology; (USA)

DOI:https://doi.org/10.1210/endo-126-4-2015· OSTI ID:6897245

Jones, J I; Fitzpatrick, L A ^[1]

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1. Univ. of Texas Health Science Center, San Antonio (USA)

The parathyroid cell is unusual, in that an increase in extracellular calcium concentrations inhibits PTH release. Calcium channels are glycoproteins that span cell membranes and allow entry of extracellular calcium into cells. We have demonstrated that the calcium channel agonist (+)202-791, which opens calcium channels, inhibits PTH release and that the antagonist (-)202-791, which closes calcium channels, stimulates PTH release. To identify the calcium channels responsible for these effects, we used a radioligand that specifically binds to calcium channels. Bovine parathyroid cell membranes were prepared and incubated under reduced lighting with (125I) iodipine (SA, 2000 Ci/mmol), which recognizes 1,4-dihydropyridine-sensitive calcium channels. Bound ligand was separated from free ligand by rapid filtration through Whatman GF/B filters. Nonspecific binding was measured by the inclusion of nifedipine at 10 microM. Specific binding represented approximately 40% of the total binding. The optimal temperature for (125I) iodipine binding was 4 C, and binding reached equilibrium by 30 min. The equilibrium dissociation constant (Kd) was approximately 550 pM, and the maximum number of binding sites was 780 fmol/mg protein. Both the calcium channel agonist (+)202-791 and antagonist (-)202-791 competitively inhibited (125I) iodipine binding, with 50% inhibition concentrations of 20 and 300 nM, respectively. These data indicate the presence of dihydropyridine-sensitive calcium channels on parathyroid cell membranes.

• OSTI ID: 6897245
• Journal Information: Endocrinology; (USA), Journal Name: Endocrinology; (USA) Vol. 126:4; ISSN ENDOA; ISSN 0013-7227
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALINE EARTH METALS
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BODY
CALCIUM
CARDIOVASCULAR AGENTS
CELL CONSTITUENTS
CELL MEMBRANES
DAYS LIVING RADIOISOTOPES
DRUGS
ELECTRON CAPTURE RADIOISOTOPES
ELEMENTS
ENDOCRINE GLANDS
GLANDS
HORMONES
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIGANDS
MEMBRANE PROTEINS
MEMBRANE TRANSPORT
MEMBRANES
METALS
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
ORGANS
PARATHORMONE
PARATHYROID GLANDS
PEPTIDE HORMONES
PORINS
PROTEINS
RADIOISOTOPES
REACTION KINETICS
RECEPTORS
SECRETION
TRACER TECHNIQUES
VASODILATORS