Hyperpolarization-activated cyclic nucleotide-gated channels may contribute to regional anesthetic effects of lidocaine.

Abstract

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. 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. 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). 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.