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Neuronal voltage-dependent potassium (K) currents are crucial for various cellular functions, such as the integration of temporal information in the central nervous system. Data for the effects of intravenous anesthetics on human neuronal K currents are limited. It was the authors’ aim to evaluate the concentration-related effects of three opioids (fentanyl, alfentanil, sufentanil) and seven nonopioids (thiopental, pentobarbital, methohexital, propofol, ketamine, midazolam, droperidol) used in clinical anesthesia on neuronal voltage-dependent K currents of human origin.K currents were measured in SH-SY5Y cells using the whole cell patch-clamp technique. Currents were elicited by step depolarization from a holding potential of −80 to −50 mV through +90 mV, and their steady state amplitudes were determined.All drugs inhibited the K currents in a concentration-dependent and reversible manner. Because time dependence of inhibition differed among the drugs, effects were measured after 54–64 ms of the test pulse. The IC50 values (concentration of half-maximal inhibition) for current suppression ranged from 7 μM for sufentanil to 2 mM for pentobarbital. Suppression of the K currents by the opioids occurred at 10-fold lower IC50 values (concentration of half-maximal inhibition) than that by the barbiturates. As estimated from the concentration–response curves, K-current suppression at clinical concentrations would be less than 0.1% for the opioids and approximately 3% for the other drugs.Effects of intravenous anesthetics on voltage-dependent K currents occur at clinical concentrations. The IC50 values for current inhibition of the nonopioid anesthetics correlated with these concentrations (r = 0.95). The results suggest that anesthetic drug action on voltage-dependent K currents may contribute to clinical effects or side effects of intravenous anesthetics.