Subterranean mole-rats naturally have an impoverished calciol status, yet synthesize calciol metabolites and calbindins.
Mole-rats (Family Bathyergidae) have no obvious source of calciol. They live in an environment devoid of sunlight and consume a herbivorous diet. Calciol status, metabolism and expression were examined in six species of Bathyergids. Serum levels of calcidiol in all species were < 5 micrograms/l and those of calcitriol were low (18.0 +/- 11.0 (SD) ng/l, N = 57) when compared to other rodents. Within 72 h of injecting animals with tritium-labelled calciol, most of the labelled prohormone had been metabolized to more polar metabolites. Three times more tritium-labelled calcitriol (19.3 +/- 2.9%) was present than (24R)-hydroxycalcidiol (6.2 +/- 10%). The natural absence of detectable circulating concentrations of calcidiol and the threefold greater amount of calcitriol to (24R)-hydroxycalcidiol produced indicate that calciol naturally is in short supply. Calciol-dependent calbindins were absent in the duodenum. Calbindin-D28k was present in the Purkinje cells of the cerebellum and in some collecting ducts and proximal and distal convoluted tubules of the kidney. Calbindin-D9k also was present but was localized uniquely in the juxtaglomerular cells of the five southern African species. These data confirm that Bathyergid mole-rats naturally have an impoverished calciol status. Despite the presence of calbindins in renal tissues, the functional importance of this hormone in calbindin synthesis and other normal mole-rat physiology is not known.
Buffenstein
R
R
Department of Physiology, Medical School, University of the Witwatersrand, Parktown, South Africa.
Jarvis
J U
JU
Opperman
L A
LA
Cavaleros
M
M
Ross
F P
FP
Pettifor
J M
JM
D000818:Animals; D064092:Calbindin 1; D064026:Calbindins; D002112:Calcifediol / Q000032:analysis / Q000096:biosynthesis* / Q000097:blood; D002117:Calcitriol / Q000032:analysis / Q000096:biosynthesis* / Q000097:blood; D002531:Cerebellum / Q000737:chemistry; D002762:Cholecalciferol / Q000008:administration & dosage / Q000493:pharmacokinetics*; D002855:Chromatography, Thin Layer; D004386:Duodenum / Q000737:chemistry; D005260:Female; D007150:Immunohistochemistry; D007668:Kidney / Q000737:chemistry; D012377:Rodentia / Q000097:blood / Q000378:metabolism*; D064030:S100 Calcium Binding Protein G / Q000032:analysis / Q000096:biosynthesis*
C576500:Calb1 protein, rat; D064092:Calbindin 1; D064026:Calbindins; D064030:S100 Calcium Binding Protein G; C576508:S100g protein, rat; D002762:Cholecalciferol; D002117:Calcitriol; D002112:Calcifediol