The opioid methadone induces a local anaesthetic-like inhibition of the cardiac Na⁺ channel, Na(v)1.5.

BACKGROUND AND PURPOSE: Treatment with methadone is associated with severe cardiac arrhythmias, a side effect that seems to result from an inhibition of cardiac hERG K⁺ channels. However, several other opioids are inhibitors of voltage-gated Na⁺ channels. Considering the common assumption that an inhibition of the cardiac Na⁺ channel Na(v)1.5, is the primary mechanism for local anaesthetic (LA)-induced cardiotoxicity, we hypothesized that methadone has LA-like properties leading to a modulation of Na(v)1.5 channels. EXPERIMENTAL APPROACH: The whole-cell patch clamp technique was applied to investigate the effects of methadone on wild-type and mutant human Na(v)1.5 channels expressed in HEK293 cells. A homology model of human Na(v)1.5 channels was used to perform automated ligand-docking studies. KEY RESULTS: Methadone inhibited Na(v)1.5 channels in a state-dependent manner, that is, tonic block was stronger with inactivated channels than with resting channels and a use-dependent block at 10 Hz. Methadone induced a concentration-dependent shift of the voltage dependency of both fast and slow inactivation towards more hyperpolarized potentials, and impaired recovery from fast and slow inactivation. The LA-insensitive mutants N406K and F1760A exhibited reduced tonic and use-dependent block by methadone, and docking predictions positioned methadone in a cavity that was delimited by the residue F1760. Dextromethadone and levomethadone induced discrete stereo-selective effects on Na(v)1.5 channels. CONCLUSIONS AND IMPLICATIONS: Methadone interacted with the LA-binding site to inhibit Na(v)1.5 channels. Our data suggest that these channels are a hitherto unrecognized molecular component contributing to cardiac arrhythmias induced by methadone.

The uretero-vesical jet as a functional diagnostic tool in childhood hydronephrosis.

Childhood hydronephrosis (HN) is accurately detected by ultrasound (US), but its functional work-up remains a domain of scintigraphy, the Whitaker-test, and clinical follow-up. We utilized color doppler US (CD-Jet) of uretero-vesical jets (UVJ) to visualize the post-obstructive ureteral flow in childhood HN. A total of 177 standardized CD-Jet were performed in 132 children aged 1 day to 14.9 years. Sixty-nine investigations in 43 patients with unilateral HN were compared with a standardized technetium 99m-mercaptotriacetylglycine nephrogram; in 10 infants both procedures were performed consecutively on the same day. UVJ were visible in 96% of all investigations. Ureteral obstruction resulted in absence of UVJ in 85% of examinations; in the remaining 15% the jet frequency was less than 10% observed in the contralateral control. Results are highly significant in both uretero-pelvic (P < 0.00007) and uretero-vesical lesions (P < 0.00005, Wilcoxon test) and are reproducible in sequential investigations. In nonobstructive distal HN the jet frequency averaged 70% of the unaffected side (P < 0.05). In proximal lesions it is equal. Jet evaluation in reflux nephropathy did not differ from controls. Compared with scintigraphy, CD-US identifies obstruction with a specificity of 94.2% and sensitivity of 94.8%. CD-US of UVJ therefore may serve as a reliable screening parameter in unilateral childhood HN.