Functional Assessment of hNav1.x Ion Channels Using State- Dependent Protocols on the QPatch HT Automated Patch Clamp System
Voltage-gated sodium channels are transmembrane proteins that are responsible for the rapid depolarization that elicits the upstroke of action potentials in neurons and cardiac cells. Molecular cloning techniques have identified nine related voltage-gated sodium channels subtypes with distinct biophysical properties, interacting proteins, and cellular patterns of expression that are involved in electrical signaling. The goal of many research groups is to target specific sodium channels subtypes to develop selective inhibitors that could, in theory, produce safer and more efficacious drugs. To address compound sodium subtype profiling, we used a two-pulse
state-dependent protocol to develop a sub-type specific sodium channel (hNav1.1 to hNav1.8) panel on the QPatch HT patch clamp system. Additionally, we tested three stimulus protocols on hNav1.5 with known sodium inhibitors: 1) CiPA protocol for cardiac safety testing (tonic), 2) two-pulse state-dependent protocol (inactivation-dependent), 3) three-pulse protocol (tonic, inactivation-dependent, and V1/2 dependent inactivation). The CiPA protocol identified state-independent compounds (e.g. Flecainide) within three-fold of published
literature values but didn’t identify state-dependent compounds such as Lidocaine. The two-pulse protocol identified both state-dependent and independent compounds at pulse 2 with IC50 values within 4-fold published literature values. Data from the first two pulses of the three-pulse protocol had comparable pharmacology to the two-pulse protocol. The functional activity from V1/2 inactivation (a delayed 3rd pulse) was less predictive of state-dependent inhibition than the two-pulse protocol but may reflect the in vivo inhibition. The hNav1.x panel using the two-pulse protocol can be useful to profile target identification, selectivity and state-dependence of novel compounds. (QPatch Automated Patch Clamp System is manufactured by Sophion Bioscience).