Open AccessComparison and characterization of retinal pericytes and retinal pigment epithelial cells on subcellular IP 3 ‐sensitive Ca2+ pools
Author(s) -
Li W.,
Ye X.,
Tao L.,
Zhan Y.,
Cohen S.,
Yanoff M.
Publication year - 1992
Publication title -
cell proliferation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.647
H-Index - 74
eISSN - 1365-2184
pISSN - 0960-7722
DOI - 10.1111/j.1365-2184.1992.tb01467.x
Subject(s) - retinal , population , cell fractionation , dissociation constant , membrane , biology , retinal pigment epithelium , retina , intracellular , biochemistry , chemistry , biophysics , microbiology and biotechnology , receptor , demography , neuroscience , sociology
. A comparative study of inositol 1,4,5‐trisphosphate (IP 3 )‐induced Ca 2+ mobilization in bovine retinal capillary pericytes (BRCP) and bovine retinal pigment epithelial cells (BRPE) was carried out. Both cells were permeabilized with saponin. The two cell types had similar basal levels of [Ca 2+ ]i (130 nM for BRCP, 132 nM for BRPE) and responded to IP, in a dose‐dependent manner. However, when stimulated by various concentrations of IP 3 (1–10 μM ) , the increase in [Ca 2+ ]i of BRCP was always two‐ to threefold higher than that in BRPE. Subcellular‐fractionation studies showed that a single population of IP 3 binding site with a high affinity and high specificity of IP 3 mainly localized to plasma membrane in these two cell types. Although the dissociation constant of specific [ 32 P]‐IP 3 binding sites (Kd 1.9–2.8 nM) was similar, the profile of maximal binding capacity (Bmax) of each fraction was markedly different. In comparison, plasma membrane fractions of BRCP were with Bmax of 165 fmol/mg protein versus 90 fmol/mg protein for BRPE membranes. The ATP‐dependent Ca 2 uptake and IP 3 ‐dependent Ca 2+ release were observed in the both plasma membrane fractions. With quantitative correlation, the membrane fraction (2 mg) of BRCP released 0.2 nmol Ca 2+ whereas BRPE only released 0.07 nmol Ca 2+ with the same dose of IP 3 (5 μM ). The selectively higher density of IP, binding sites in coupling to the larger Ca 2+ ‐release in the membrane of BRCP suggests that the quantity of Ca 2+ mobilized is determined by the spatially preferential distribution of membrane‐associated IP 3 binding sites. These findings may provide an explanation for the differences observed between BRCP and BRPE in IP,‐induced DNA replication.