Gentamicin Inhibits Ca Channel TRPV5 and Induces Calciuresis Independent of the Calcium-Sensing Receptor-Claudin-14 Pathway.

Background: Treatment with the aminoglycoside antibiotic gentamicin can be associated with severe adverse effects, including renal Ca wasting. The underlying mechanism is unknown but it has been proposed to involve activation of the Ca-sensing receptor (CaSR) in the thick ascending limb, which would increase expression of claudin-14 (CLDN14) and limit Ca reabsorption. However, no direct evidence for this hypothesis has been presented.

Methods: We studied the effect of gentamicin using mouse models with impaired Ca reabsorption in the proximal tubule and the thick ascending limb. We used a promoter luciferase reporter assay to study CaSR activation and investigated the effect of gentamicin on activity of the distal nephron Ca channel transient receptor potential vanilloid 5 (TRPV5), as determined by patch clamp in HEK293 cells.

Results: Gentamicin increased urinary Ca excretion in wild-type mice after acute and chronic administration. This calciuretic effect was unaltered in mice with genetic CaSR overactivation and was present in furosemide-treated animals, whereas the calciuretic effect in mice and mice with impaired proximal tubular Ca reabsorption (claudin-2 [CLDN2]-deficient mice) was equivalent to that of wild-type mice. , gentamicin failed to activate the CaSR. In contrast, patch clamp analysis revealed that gentamicin strongly inhibited rabbit and human TRPV5 activity and chronic gentamicin administration downregulated distal nephron Ca transporters.

Conclusions: Gentamicin does not cause hypercalciuria activation of the CaSR-CLDN14 pathway or by interfering with proximal tubular CLDN2-dependent Ca reabsorption. Instead, gentamicin blocks distal Ca reabsorption by direct inhibition of the Ca channel TRPV5. These findings offer new insights into Ca wasting in patients treated with gentamicin.