Biophysical and Pharmacological Profiling of Multiple Voltage-Gated Sodium Channel Subtypes on QPatch II

Abstract

Voltage - gated sodium channels (VGSC) are responsible for the initiation and propagation of action potentials in excitable cells. VGSC have been identified as excellent drug targets for treatment of pain, epilepsy and to other neurological disorders. Early compounds, however, were developed using empirical approaches. The identification of the molecular identity of VGSC in combination with technological advances, such as the automated patch clamp technique, provide the basis for a rational design of subtype – selective compounds. To date, 9 functional mammalian isoforms (NaV1.1–1.9) have been described in the literature. The various subtypes differ in their expression pattern and exhibit distinct biophysical and pharmacological profiles. All have in common that they produce a transient inward current in response to membrane depolarization. During this process the VGSC transitions from a closed to and open into an inactivated state. Interestingly, inhibitor compounds often exhibit different pharmacological profiles dependent upon the ion channel conformational state. In the present study, the second generation QPatch (QPatch II; Sophion Bioscience) was used in combination with adaptive voltage protocols to investigate state-dependent inhibition of tetrodotoxin (TTX) and tetracaine on 8 different VGSC subtypes (NaV1.1-8). A first step was to determine the half inactivation potential V½(inactivation) for each individual cell. This value was then used during the next steps as preconditioning pulse. Such an adaptive protocol allowed to determine IC50 values for both the closed and the inactivated state and reduce heterogeneity of the cells. Both IC50 values and biophysical parameters of the different subtypes align well with literature values.