Absence of Calcitriol-Mediated Nongenomic Actions in Isolated Intestinal Cells of the Damara Mole-Rat (Cryptomys damarensis)

Calcitriol [1,25(OH)₂D₃] actions on intestinal calcium transport involve genomic and nongenomic pathways. Whether nongenomic 1,25(OH)₂D₃-mediated actions are employed was investigated using isolated intestinal epithelial cells of naturally vitamin D-deficient underground-dwelling damara mole-rats (Cryptomys damarensis). 1,25(OH)₂D₃-mediated nongenomic pathways of intestinal calcium uptake, measured by opening of 1,25(OH)₂D₃-activated voltage-sensitive Ca²⁺ channels (VSCC), did not occur. Rapid (1 min) ⁴⁵Ca²⁺ transmembrane influx in intestinal cells was not significantly increased by the addition of 1,25(OH)₂D₃ (at concentrations from 10^-12 to 10^-6 nM), when compared to opening of VSCC in the presence of a depolarizing (elevated K+) buffer. Furthermore, even after 30 min calcium uptake was not significantly enhanced by the hormone. These findings support earlier reports that duodenal calcium absorption is independent of vitamin D and is a highly adaptive feature of a subterranean existence.