The effects of rises in external K+ on the hyperpolarization-activated cation current Ih in rat dorsal root ganglion neurons

The effects of rises in external K⁺ (K_ext) were examined on the hyperpolarization-activated cation current (I _h) in rat dorsal root ganglion neurons using the whole-cell patch clamp technique. The results showed that K_ext increased I _h in a certain concentration and voltage-dependent manner. At the basal K_ext level (4 mmol/L), I _h had a maximal amplitude of 1085 ± 340 pA which was enhanced by ∼45% and ∼92% at 8 and 16 mmol/L K_ext, respectively. The midpoint activation voltage was significantly shifted from −98 mV in the hyperpolarizing direction by 8 and 12 mV at 8 and 16 mmol/L K_ext, respectively with alteration of the activation course of I _h. The short time constants of activation became longer with the increasing amplitude of the command potential upon rises in K_ext. The long time constants became shorter. The reversal potentials were shifted in the positive direction without significant alterations upon rises in K_ext. According to the functional role of I _h, K_ext increased I _h, resulting in an enhanced neuronal excitability, which might produce activation potential abnormality and perhaps neuropathic pain involved. Supported by the University of Science and Technology Foundation of Shanxi Province (Grant No. 200713010)