Fenja Knoepp, Joerg Bettmer, Martin Fronius

Gadolinium-based-contrast-agents (GBCAs) are used for magnetic-resonance-imaging and associated with renal and cardiovascular adverse reactions caused by released Gd(3+) ions. Gd(3+) is also a modulator of mechano-gated ion channels, including the epithelial Na(+) channel (ENaC) that is expressed in kidney epithelium and the vasculature. ENaC is important for salt-/water homeostasis and blood pressure regulation and a likely target of released Gd(3+) from GBCAs causing the above-mentioned adverse reactions. Therefore this study examined the effect of Gd(3+) and GBCAs on ENaC's activity. Human αβγENaC was expressed in Xenopus laevis oocytes and exposed to Gd(3+), linear (Gd-DTPA, Magnevist) or cyclic (Dotarem) GBCAs. Transmembrane ion-currents (IM) were recorded by the two-electrode-voltage-clamp technique and Gd(3+)-release by Gd-DTPA was confirmed by inductively coupled plasma-mass spectrometry. Gd(3+) exerts biphasic effects on ENaC's activity: ≤0.3mmol/l decreased IM which was preventable by DEPC (modifies histidines). Strikingly Gd(3+)≥0.4mmol/l increased IM and this effect was prevented by cysteine-modifying MTSEA. Linear Gd-DTPA and Magnevist mimicked the effect of ≤0.3mmol/l Gd(3+), whereas the chelator DTPA showed no effect. Gd(3+) and Gd-DTPA increased the IC50 for amiloride, but did not affect ENaC's self-inhibition. Interestingly, cyclic Gd-DOTA (Dotarem) increased IM to a similar extent as its chelator DOTA, suggesting that the chelator rather than released Gd(3+) is responsible for this effect. These results confirm Gd(3+)-release from linear Gd-DTPA and indicate that the released Gd(3+) amount is sufficient to interfere with ENaC's activity to provide putative explanations for GBCA-related adverse effects.