Effects of cytochalasin B on calcium transport by 1,25(OH)2D3- or PTH-treated chick embryonic yolk sac in vitro and in vivo.
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 degree C had no significant effect on calcium uptake by the yolk sac membrane. Dinitrophenol (DNP) and lanthanum chloride (LaCl2) reduced 45Ca uptake from day 6 and 9 embryos by 15% and 30%, respectively. Cytochalasin B decreased the uptake of 45Ca 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)2D3 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 45Ca uptake into yolk sac disks by about 50% in embryos of all age groups tested. We also examined the effect of cytochalasin B on 45Ca 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 45Ca transport in day-9 and -12 vitamin D-treated embryos approximately 30% and 45%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Medicine, University of Connecticut, Farmington.
S K
SK
Lee
N B
NB
Clark
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002117:Calcitriol / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002642:Chick Embryo; D046508:Culture Techniques; D003571:Cytochalasin B / Q000494:pharmacology*; D008566:Membranes / Q000378:metabolism; D010281:Parathyroid Hormone / Q000494:pharmacology; D015017:Yolk Sac / Q000187:drug effects / Q000378:metabolism*
D010281:Parathyroid Hormone; D003571:Cytochalasin B; D002117:Calcitriol; D002118:Calcium