Dihydropyridines interact with calcium-independent potassium currents in embryonic mammalian sensory neurons

Early embryonic sensory neurons have two K currents resembling delayed rectifier and transient K currents of mature neurons. However, in contrast to those of adult neurons, the embryonic currents can hardly be separated either by electrophysiological or pharmacological methods, limiting their characterisation at these developmental stages. Using the whole-cell recording technique, we found that dihydropyridines (DHPs) inhibit the noninactivating component of the Ca-independent K currents of 13-day mouse embryo dorsal-root ganglion (DRG) cells. The inhibitory effect of nicardipine began around 0.5 microM and was nearly complete at 5 microM while Na currents were not altered. This effect was reversible and voltage-dependent. The same results were obtained using another DHP Ca antagonist, nimodipine, whereas Bay K 8644, a DHP Ca agonist, had no effect. Kinetic properties of the DHP-insensitive K current have been described and compared with those of transient K currents found in differentiated neurons. These results suggest that both Ca and K channels have DHP sites, possibly homologous, at this developmental stage. The DHP inhibition of Ca-independent K channels provides a new tool with which to study K channels both at a molecular level and during DRG development.