Effects of cytochalasin B on calcium transport by 1,25(OH)2D3- or PTH-treated chick embryonic yolk sac in vitro and in vivo
✍ Scribed by Lee, S. Kyeong ;Clark, Nancy B.
- Publisher
- John Wiley and Sons
- Year
- 1993
- Tongue
- English
- Weight
- 711 KB
- Volume
- 266
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
Abstract
The present study was done to elucidate the mechanism(s) by which calcium is taken up or transported across the yolk sac membrane of the embryonic chick. We examined the effect of various inhibitors or experimental conditions on the uptake of calcium in vitro. Treatment with ouabain, verapamil, antimycin A and calcium ionophore A23187; substitution of choline for sodium or potassium in the buffer; or incubation of the tissue at 0°C had no significant effect on calcium uptake by the yolk sac membrane. Dinitrophenol (DNP) and lanthanum chloride (LaCl~2~) reduced ^45^Ca uptake from day 6 and 9 embryos by 15% and 30%, respectively. Cytochalasin B decreased the uptake of ^45^Ca in yolk sac membrane disks of day 6 embryos, but not in older embryos. The effects of cytochalasin B were explored further in embryos pretreated with either 1,25(OH)~2~D~3~ or PTH, both of which enhance calcium uptake. Cytochalasin B decreased calcium uptake in 9‐day and 12‐day vitamin D‐treated embryos to about 60% of their hormone‐enhanced level and also decreased PTH‐stimulated ^45^Ca uptake into yolk sac disks by about 50% in embryos of all age groups tested.
We also examined the effect of cytochalasin B on ^45^Ca transport across the yolk sac membrane in vivo. Cytochalasin B did not affect this transport in control (vehicle‐treated) embryos. However, it significantly decreased the enhanced in vivo ^45^Ca transport in day‐9 and ‐12 vitamin D‐treated embryos approximately 30% and 45%, respectively. Additionally, cytochalasin B decreased the transport of calcium from yolk to blood by about 40% in PTH‐treated day‐9 embryos. These results indicated that both calcium uptake and transport by hormone‐stimulated yolk sac membranes involves endocytosis but that some other mechanism(s) must also be involved. © 1993 Wiley‐Liss, Inc.