Effect of rabbit duodenal mRNA on phosphate transport in Xenopus laevis oocytes: dependence on 1,25-dihydroxy-vitamin-D3.
Expression of Na(+)-dependent transport of phosphate (Pi) was analysed in Xenopus laevis oocytes after injection of poly(A)-rich RNA isolated from the duodenal mucosa of rabbits with increased levels of 1,25-(OH)2-VitD3 (injection of vitamin D3 or low-Pi diet) or from control animals. In parallel, the effect of elevated levels of vitamin D3 was studied in isolated duodenal brush-border membrane vesicles. In brush-border membrane vesicles, the rate of Na(+)-Pi cotransport was found to be doubled after 1,25-(OH)2-VitD3 injections while Na(+)-D-glucose cotransport (measured as a control) was not altered. In X. laevis oocytes, Na(+)-dependent Pi uptake was increased after injection of poly(A)-rich RNA isolated from duodenal mucosa of animals with increased levels of 1,25-(OH)2-VitD3 but not after injection of poly(A)-rich RNA isolated from control animals; between the two groups of mRNA no difference in the expression of the Na(+)-D-glucose transport system was observed. Sucrose density gradient fractionation suggests that mRNA species related to the increased Na(+)-dependent Pi uptake are of average chain lengths between 2 x 10(3) and 3 x 10(3) bases (2-3 kb). It is concluded that in duodenal enterocytes 1,25-(OH)2-VitD3 increases the content of mRNA species of 2-3 kb that might be involved either directly in Na-Pi cotransport or at least in controlling its activity.
Yagci
A
A
Institute of Physiology, University of Zürich, Switzerland.
Werner
A
A
Murer
H
H
Biber
J
J
D000818:Animals; D002117:Calcitriol / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism*; D004386:Duodenum / Q000033:anatomy & histology / Q000187:drug effects*; D005260:Female; D008297:Male; D008871:Microvilli / Q000187:drug effects*; D009865:Oocytes / Q000378:metabolism*; D012333:RNA, Messenger / Q000008:administration & dosage*; D011817:Rabbits; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D012333:RNA, Messenger; D050608:Sodium-Phosphate Cotransporter Proteins; D027981:Symporters; D002117:Calcitriol