Effect of vitamin D depletion on calcium transport by the luminal and basolateral membranes of the proximal and distal nephrons.
To study the effect of vitamin D on calcium (Ca2+) reabsorption by the kidney, we measured Ca2+ uptake by the basolateral and luminal membranes of proximal and distal tubules obtained from rabbits fed a vitamin D-deficient diet for 3 weeks. Results were compared to those obtained with a group of control animals fed a normal diet. Serum Ca2+ concentrations were comparable in both groups. In the control group, serum PTH, 25-hydroxyvitamin D3, and 1,25-dihydroxyvitamin D3 remained relatively stable. In the vitamin D-deficient animals, serum PTH levels slightly, but not significantly, increased, and the levels of vitamin D metabolites abruptly fell. Vitamin D depletion produced a 40% decrease in ATP-dependent Ca2+ uptake by the basolateral membrane of the distal tubule. There was no change in the activity of the Na+/Ca2+ exchanger. A very significant effect was also observed in the luminal membrane of the distal tubule, where a 50% decrease in Ca2+ uptake was observed after the third week of vitamin depletion. Administration of 0.1 microgram 1,25-dihydroxyvitamin D3 16 and 2 h before death partially reestablished normal uptake. In contrast, no change in Ca2+ uptake could be detected in the basolateral or luminal membranes of the proximal tubule. These observations provide the first evidence of an effect of vitamin D on Ca2+ transport at both the basolateral and luminal membranes of the distal segment of the nephron.
Bouhtiauy
I
I
Maisonneuve-Rosemont Hospital, Montreal, Quebec, Canada.
Lajeunesse
D
D
Brunette
M G
MG
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002117:Calcitriol / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D007686:Kidney Tubules, Distal / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D009399:Nephrons / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000097:blood; D011817:Rabbits; D019831:Sodium-Calcium Exchanger; D014807:Vitamin D / Q000097:blood; D014808:Vitamin D Deficiency / Q000378:metabolism*
D002352:Carrier Proteins; D010281:Parathyroid Hormone; D019831:Sodium-Calcium Exchanger; D014807:Vitamin D; D000255:Adenosine Triphosphate; D002117:Calcitriol; D002118:Calcium