Dual pathways of calcium entry in spike and plateau phases of luteinizing hormone release from chicken pituitary cells: sequential activation of receptor-operated and voltage-sensitive calcium channels by gonadotropin-releasing hormone
It has previously been shown that, in pituitary gonadotrope cells, the initial rise in cytosolic Ca2+ induced by GnRH is due to a Ca2+ mobilization from intracellular stores. This raises the possibility that the initial transient spike phase of LH release might be fully or partially independent of extracellular Ca2+. We have therefore characterized the extracellular Ca2+ requirements, and the sensitivity to Ca2+ channel blockers, of the spike and plateau phases of secretion separately. In the absence of extracellular Ca2+ the spike and plateau phases were inhibited by 65 +/- 4% and 106 +/- 3%, respectively. Both phases exhibited a similar dependence on concentration of extracellular Ca2+. However, voltage-sensitive Ca2+ channel blockers D600 and nifedipine had a negligible effect on the spike phase, while inhibiting the plateau phase by approximately 50%. In contrast, ruthenium red, Gd3+ ions, and Co2+ ions inhibited both spike and plateau phases to a similar extent as removal of extracellular Ca2+. A fraction (35 +/- 4%) of spike phase release was resistant to removal of extracellular Ca2+. This fraction was abolished after calcium depletion of the cells by preincubation with EGTA in the presence of calcium ionophore A23187, indicating that it depends on intracellular Ca2+ stores. Neither absence of extracellular Ca2+, nor the presence of ruthenium red or Gd3+ prevented mobilization of 45Ca2+ from intracellular stores by GnRH. We conclude that mobilization of intracellular stored Ca2+ is insufficient by itself to account for full spike phase LH release.
- Research Organization:
- Univ. of Cape Town Medical School Observatory (South Africa)
- OSTI ID:
- 6974958
- Journal Information:
- Mol. Endocrinol.; (United States), Vol. 2:4
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
CALCIUM
BIOLOGICAL PATHWAYS
LH
SECRETION
CALCIUM 45
CATIONS
CHICKENS
COBALT COMPOUNDS
EGTA
GADOLINIUM COMPOUNDS
KINETICS
PITUITARY GLAND
PORINS
POTASSIUM
TRACER TECHNIQUES
ALCOHOLS
ALKALI METALS
ALKALINE EARTH ISOTOPES
ALKALINE EARTH METALS
ANIMALS
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
BIRDS
BODY
CALCIUM ISOTOPES
CARBOXYLIC ACIDS
CHARGED PARTICLES
CHELATING AGENTS
DAYS LIVING RADIOISOTOPES
ELEMENTS
ENDOCRINE GLANDS
EVEN-ODD NUCLEI
FOWL
GLANDS
GLYCOLS
GONADOTROPINS
HORMONES
HYDROXY COMPOUNDS
INTERMEDIATE MASS NUCLEI
IONS
ISOTOPE APPLICATIONS
ISOTOPES
MEMBRANE PROTEINS
METALS
NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANS
PEPTIDE HORMONES
PITUITARY HORMONES
PROTEINS
RADIOISOTOPES
RARE EARTH COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
VERTEBRATES
550201* - Biochemistry- Tracer Techniques