Characterization of temperature-sensitive leak K⁺ currents and expression of TRAAK, TREK-1, and TREK2 channels in dorsal root ganglion neurons of rats

Leak K⁺ currents are mediated by two-pore domain K⁺ (K2P) channels and are involved in controlling neuronal excitability. Of 15 members of K2P channels cloned so far, TRAAK, TREK-1, and TREK-2 are temperature sensitive. In the present study, we show that strong immunoreactivity of TRAAK, TREK-1 and TREK-2 channels was present mainly in small-sized dorsal root ganglion (DRG) neurons of rats. The percentages of neurons with strong immunoreactivity of TRAAK, TREK-1 and TREK-2 channels were 27, 23, and 20%, respectively. Patch-clamp recordings were performed to examine isolated leak K⁺ currents on acutely dissociated small-sized rat DRG neurons at room temperature of 22 °C, cool temperature of 14 °C and warm temperature of 30 °C. In majority of small-sized DRG neurons recorded (76%), large leak K⁺ currents were observed at 22 °C and were inhibited at 14 °C and potentiated at 30 °C, suggesting the presence of temperature-sensitive K2P channels in these neurons. In a small population (18%) of small-sized DRG neurons, cool temperature of 14 °C evoked a conductance which was consistent with TRPM8 channel activation in cold-sensing DRG neurons. In these DRG neurons, leak K⁺ currents were very small at 22 °C and were not potentiated at 30 °C, suggesting that few temperature-sensitive K2P channels was present in cold-sensing DRG neurons. For DRG neurons with temperature-sensitive leak K⁺ currents, riluzole, norfluoxetine and prostaglandin F2α (PGE2α) inhibited the leak K⁺ currents at both 30 °C and 22 °C degree, and did not have inhibitory effects at 14 °C. Collectively, the observed temperature-sensitive leak K⁺ currents are consistent with the expression of temperature-sensitive K2P channels in small-sized DRG neurons.