Hyperpolarization-activated Cyclic Nucleotide-gated Channels May Contribute to Regional Anesthetic Effects of Lidocaine
Abstract Background: Local anesthetics (e.g., lidocaine) have been found to inhibit hyperpolarization-activated cyclic nucleotide-gated (HCN) channels besides sodium channels. However, the exact role of HCN channels in regional anesthesia in vivo is still elusive. Methods: Sciatic nerve block and intrathecal anesthesia were performed using lidocaine in wild-type and HCN1 channel knockout (HCN1−/−) mice. EC50 of lidocaine and durations of 1% lidocaine were determined. In electrophysiologic recordings, effects of lidocaine on HCN channel currents, voltage-gated sodium channel currents, and neural membrane properties were recorded on dorsal root ganglia neurons. Results: In both sciatic nerve block and intrathecal anesthesia, EC50 of lidocaine for tactile sensory blockade (2 g von Frey fiber) was significantly increased in HCN1−/− mice, whereas EC50 of lidocaine for pinprick blockade was unaffected. Durations of 1% lidocaine were significantly shorter in HCN1−/− mice for both sciatic nerve block and intrathecal anesthesia (n = 10). ZD7288 (HCN blocker) could significantly prolong durations of 1% lidocaine including pinprick blockade in sciatic nerve block (n = 10). Forskolin (raising cyclic adenosine monophosphate to enhance HCN2) could significantly shorten duration of pinprick blockade of 1% lidocaine in sciatic nerve block (n = 10). In electrophysiologic recordings, lidocaine could nonselectively inhibit HCN channel and sodium channel currents both in large and in small dorsal root ganglia neurons (n = 5 to 6). Meanwhile, lidocaine caused neural membrane hyperpolarization and increased input resistance of dorsal root ganglia neurons but not in large dorsal root ganglia neurons from HCN1−/− mice (n = 5–7). Conclusions: These data indicate that HCN channels may contribute to regional anesthetic effects of lidocaine. By inhibiting HCN channels, lidocaine could alter membrane properties of neurons.