Heterologous expression of the human wild-type and variant Na_V 1.8 (A1073V) in rat sensory neurons

Silent inflammatory bowel disease (IBD) is a condition in which individuals with the active disease experience minor to no pain. Voltage-gated Na⁺ (Na_V ) channels expressed in sensory neurons play a major role in pain perception. Previously, we reported that a Na_V 1.8 genetic polymorphism (A1073V, rs6795970) was more common in a cohort of silent IBD patients. The expression of this variant (1073V) in rat sympathetic neurons activated at more depolarized potentials when compared to the more common variant (1073A). In this study, we investigated whether expression of either Na_V 1.8 variant in rat sensory neurons would exhibit different biophysical characteristics than previously observed in sympathetic neurons.

Endogenous Na_V 1.8 channels were first silenced in DRG neurons and then either 1073A or 1073V human Na_V 1.8 cDNA constructs were transfected. Na_V 1.8 currents were recorded with the whole-cell patch-clamp technique.

The results indicate that 1073A and 1073V Na_V 1.8 channels exhibited similar activation values. However, the slope factor (k) for activation determined for this same group of neurons decreased by 5 mV, suggesting an increase in voltage sensitivity. Comparison of inactivation parameters indicated that 1073V channels were shifted to more depolarized potentials than 1073A-expressing neurons, imparting a proexcitatory characteristic.

These findings differ from previous observations in other expression models and underscore the challenges with heterologous expression systems. Therefore, the use of human sensory neurons derived from induced pluripotent stem cells may help address these inconsistencies and better determine the effect of the polymorphism present in IBD patients.