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Analysis of Binding Sites for IGF-I on Membranes from Granulosa Cells of Small, Medium, and Large Porcine Follicles

  • Vincent W. Hylka
  • Brigitte Caubo
  • Sharon A. Tonetta

Abstract

We examined binding of IGF-I to granulosal membranes from small (<3 mm), medium (3–6 mm) and large (>8 mm) porcine follicles. Granulosa cells were aspirated and membranes prepared by dounce homogenization. Membranes from each group were incubated for 16 h at 4°C (optimal conditions) with I-IGF-I in the absence or presence of unlabeled IGF-I (0.01–1 μg/ml), IGF-II (0.5–5 μg/ml), or insulin (0.1–20 μg/ml). Scatchard analysis of the data demonstrated a curvilinear plot for all three groups. The high-affinity sites had the following Ka values (mean ± SEM; nM): small = 6.50 ± 0.09; medium = 6.45 ± 0.44; large = 6.48 ± 0.44. The binding capacities of the high-affinity sites for each group were (pmol/mg protein): small = 1.51 ± 0.17; medium = 1.15 ± 0.14; large = 1.40 ± 0.15. The low-affinity sites had the following Ka values (nM): small = 0.053 ± 0.008; medium = 0.077 ± 0.019; large = 0.077 ± 0.007. The low-affinity sites had the following binding capacities (pmol/mg protein): small = 20.40 ± 3.10; medium = 13.76 ± 0.78; large = 12.99 ± 0.55. Preferential binding for the high-affinity sites was IGF-I > IGF-II > insulin. These data show that although IGF-I plays a role in granulosal differentiation, the affinity and number of high-affinity binding sites do not change during follicular maturation. However, the number of low-affinity binding sites appears to be greater in granulosa cells from small follicles, suggesting a possible role for IGF-II and/or insulin in early follicular maturation.

Keywords

Granulosa Cell Follicular Fluid Scatchard Analysis Large Follicle Follicular Maturation 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Plenum Press, New York 1989

Authors and Affiliations

  • Vincent W. Hylka
    • 1
  • Brigitte Caubo
    • 1
  • Sharon A. Tonetta
    • 1
  1. 1.Livingston Reproductive Biology LaboratoryUniversity of Southern California School of MedicineLos AngelesUSA

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