Temperature sensitivity of transduction and action potential conduction in a spider mechanoreceptor

Previous work has suggested that the activation energy of mechanotransduction is higher than expected from the simple electrochemistry of ion channels, but the temperature sensitivity of mechanically activated receptor current has not been measured directly before. We used the single- electrode voltage-clamp technique to measure receptor currents in sensory neurons of the VS-3 slit-sense organ in the spider, Cupiennius salei. Receptor currents were generated by deforming the cuticular slits. Conduction velocity in afferent axons from the same organ was also measured by recording action potentials at two locations in the leg during mechanical stimulation of the slits. Activation energies of mechanotransduction and conduction velocity were estimated by making the measurements at a range of temperatures. The mean activation energy for receptor current was 23.1 kcal/mol (96.6 kJ/mol), corresponding to a Q₁₀ value of 3.2. Conduction velocity in the afferent axons was ≃5 m/s at room temperature and it was much less temperature sensitive, with an activation energy of 6.3 kcal/mol (26.3 kJ/mol), corresponding to a Q₁₀ value of 1.5. These results provide the first direct measurements of the activation energy of mechanically activated currents and support previous suggestions that a high thermal energy barrier is involved in mechanotransduction.