The effects of rises in external K+ on the hyperpolarization-activated cation current I h 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 similar to 45% and similar to 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.