Effect of growth and maturation on membrane-initiated actions of 1,25-dihydroxyvitamin D3—II: Calcium transport, receptor kinetics, and signal transduction in intestine of female chickens
✍ Scribed by Birgitta Larsson; Ilka Nemere
- Publisher
- John Wiley and Sons
- Year
- 2003
- Tongue
- English
- Weight
- 195 KB
- Volume
- 90
- Category
- Article
- ISSN
- 0730-2312
No coin nor oath required. For personal study only.
✦ Synopsis
Abstract
We recently reported (Larsson and Nemere [2003]: Endocrinology 144:1726) the effects of growth and maturation on 1,25(OH)~2~D~3~‐membrane initiated effects in the intestine of male chickens. Here we extend our observations to studies on females with two stages of high calcium demand: growth (7–14 weeks) and egg laying (28–58 weeks). The rapid stimulatory effect of 130 pM 1,25(OH)~2~D~3~ on calcium transport was assessed as a physiological response in perfused duodena of 7‐, 14‐, 28‐, and 58‐week‐old chickens, and determined to be 308%, 184%, 170%, and 153%, respectively, of corresponding controls after 40 min. Saturation analyses of [^3^H]1,25(OH)~2~D~3~ binding to nuclear vitamin D receptor (VDR) indicated an absence of cooperative binding, no changes in dissociation constant (K~d~) with age, and an increase in maximum binding capacity (B~max~) between 7‐week birds and older age groups. Analyses of saturable binding of [^3^H]1,25(OH)~2~D~3~ to the membrane associated rapid response steroid binding protein (1,25D~3~‐MARRS bp) in basal lateral membranes (BLM), indicated cooperative binding, and an increase in both B~max~ and K~d~ with age. No changes in the age‐related expression of 1,25D~3~‐MARRS bp were found, as judged by Western analyses, suggesting that a shift in ligand binding to lower affinity membrane components accounted for the increase in calculated B~max~. Basal levels of protein kinase C (PKC) activity decreased with age, as did hormone enhancement of activity. Basal levels of protein kinase A (PKA) activity remained constant with age, while the magnitude of hormone stimulation increased. Comparison of dose‐response curves for ion transport and kinase activities in 7‐week chicks suggested that PKC mediates phosphate transport while PKA mediates calcium transport. Thus, the age‐related loss of calcium transport is most likely related to loss of PKC‐mediated phosphate transport. © 2003 Wiley‐Liss, Inc.