Cold and warmth intensify pain-linked sodium channel gating effects and persistent currents

Voltage gated sodium channels (Navs) play a key physiological role in excitable tissues as they generate and propagate action potentials and thus are crucial in excitability and temperature sensation. Mutations in genes encoding Navs can lead to severe inherited diseases, and some of these so-called channelopathies show temperature-sensitive phenotypes, for example for example, paramyotonia congenita, Brugada syndrome, febrile seizure syndromes, and inherited pain syndromes like erythromelalgia (IEM) and paroxysmal extreme pain disorder (PEPD). Nevertheless, most investigations of mutation-induced gating effects have been conducted at room temperature, and thus the role of body temperature, cooling or warming in channelopathies remains poorly understood. We investigated the temperature sensitivity of four Nav subtypes (expressed in HEK293 cells) using the automated patch clamp system SyncroPatch 384: Nav1.3, Nav1.5, Nav1.6, and Nav1.7, and two mutations in Nav1.7 causing IEM (Nav1.7/L823R) and PEPD (Nav1.7/I1461T). The experiments at 15°C, 25°C, and 35°C revealed a shift of the midpoint of the activation voltage dependence (V1/2) to more hyperpolarized potentials with increasing temperature for all investigated subtypes. V1/2 of steady-state fast inactivation, on the other hand, was nearly unaffected. Nav1.3 exhibited strongly slowed inactivation kinetics compared to the other subtypes that resulted in enhanced persistent current, especially at 15°C, indicating a possible role in cold-induced hyperexcitability. Impaired fast inactivation of the PEPD causing mutation Nav1.7/I1461T was significantly enhanced by cooling the temperature to 15°C. The subtype-specific modulation as well as the intensified mutation induced gating changes stress the importance to consider temperature as a regulator for channel gating and its impact on cellular excitability as well as disease phenotypes. Detailed electrophysiological investigation of Navs at different temperatures is essential to understand the properties and to gain a deeper insight into the complex gating mechanisms of Navs at physiological temperature, otherwise important effects might be missed. The data collected in this work can form the basis for the development of detailed neuronal computer models, based on Hodgkin-Huxley or Markov models, which benefit from the here provided high n-number. Understanding the altered gating mechanisms of temperature sensitive pain linked Nav mutations is also essential for the identification of potential therapeutic targets and strategies in the treatment of this diseases.