Distribution of somatostatin receptors in RINm5F insulinoma cells
Previous studies with heterogeneous populations of pancreatic cells have provided evidence for the presence of somatostatin (SRIF) receptors in cytosol and secretion vesicles, as well as the plasma membrane. To examine the distribution of SRIF receptors between soluble and membrane fractions in a homogeneous pancreatic islet cell population, we have used the clonal RINm5F insulinoma cell line. These cells contain specific, high affinity binding sites for (/sup 125/I-Try11)SRIF on the cell surface, and occupancy of these sites by SRIF and SRIF analogs correlates with inhibition of insulin secretion. Stable, steady state binding was achieved using both intact cells and membranes by performing binding incubations with (25I-Tyr11)SRIF at 22 C. Half-maximal inhibition of (/sup 125/I-Tyr11)SRIF binding occurred with 0.21 +/- 0.11 nM SRIF in membranes and 0.35 +/- 0.30 nM SRIF in cells. In contrast, the binding of (/sup 125/I-Tyr11)SRIF to cytosolic macromolecules was not reduced by concentrations of SRIF as high as 100 nM, demonstrating that this binding was of much lower affinity. RINm5F membranes were further purified using a Percoll gradient to prepare a microsomal fraction, which was enriched in adenylate cyclase activity, and a secretory granule fraction, which was enriched in insulin. (125I-Tyr11)SRIF binding to the microsomal fraction (3.8 +/- 0.3 fmol/mg) was 3 times higher than to secretion granules (1.2 +/- 0.2 fmol/mg). Thus, high affinity SRIF binding sites were most abundant in microsomal membranes and were low or undetectable in secretory granules and cytosol. To determine whether translocation of SRIF receptors to the plasma membrane accompanied insulin secretion, we examined the effects of various insulin secretagogues on (/sup 125/I-Tyr11)SRIF binding to intact cells.
- Research Organization:
- Harvard School of Public Health, Boston, MA (USA)
- OSTI ID:
- 5210486
- Journal Information:
- Endocrinology; (United States), Journal Name: Endocrinology; (United States) Vol. 122:3; ISSN ENDOA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
ANIMAL CELLS
ANIMALS
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL LOCALIZATION
BODY
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CELL MEMBRANES
DAYS LIVING RADIOISOTOPES
DIGESTIVE SYSTEM
ELECTRON CAPTURE RADIOISOTOPES
ENDOCRINE GLANDS
GLANDS
GLUCAGON
HORMONES
INSULIN
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LEUCINE
MAMMALS
MEMBRANE PROTEINS
MEMBRANES
MICROSOMES
NUCLEI
ODD-EVEN NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANOIDS
ORGANS
PANCREAS
PEPTIDE HORMONES
PEPTIDES
POLYPEPTIDES
PROTEINS
RADIOISOTOPES
RATS
REACTION KINETICS
RECEPTORS
RODENTS
SECRETION
SOMATOSTATIN
TRACER TECHNIQUES
TUMOR CELLS
VERTEBRATES