Gentamicin Inhibits Ca²⁺ Channel TRPV5 and Induces Calciuresis Independent of the Calcium-Sensing Receptor-Claudin-14 Pathway.

Abstract

Treatment with the aminoglycoside antibiotic gentamicin can be associated with severe adverse effects, including renal Ca²⁺ wasting. The underlying mechanism is unknown but it has been proposed to involve activation of the Ca²⁺-sensing receptor (CaSR) in the thick ascending limb, which would increase expression of claudin-14 (CLDN14) and limit Ca²⁺ reabsorption. However, no direct evidence for this hypothesis has been presented. We studied the effect of gentamicin <i>in vivo</i> using mouse models with impaired Ca²⁺ reabsorption in the proximal tubule and the thick ascending limb. We used a <i>Cldn14</i> promoter luciferase reporter assay to study CaSR activation and investigated the effect of gentamicin on activity of the distal nephron Ca²⁺ channel transient receptor potential vanilloid 5 (TRPV5), as determined by patch clamp in HEK293 cells. Gentamicin increased urinary Ca²⁺ 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 <i>Cldn14^-/-</i> mice and mice with impaired proximal tubular Ca²⁺ reabsorption (claudin-2 [CLDN2]-deficient <i>Cldn2^-/-</i> mice) was equivalent to that of wild-type mice. <i>In vitro</i>, 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 Ca²⁺ transporters. Gentamicin does not cause hypercalciuria <i>via</i> activation of the CaSR-CLDN14 pathway or by interfering with proximal tubular CLDN2-dependent Ca²⁺ reabsorption. Instead, gentamicin blocks distal Ca²⁺ reabsorption by direct inhibition of the Ca²⁺ channel TRPV5. These findings offer new insights into Ca²⁺ wasting in patients treated with gentamicin.