Calcium-independent Potassium Current Research Articles

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.

Features of a calcium independent, caffeine sensitive outward current in single smooth muscle cells from guinea pig portal vein

Using the single electrode voltage-clamp technique, vascular smooth muscle cells from the guinea pig portal vein showed an initial inward (Ca2+) current followed by an outward current which peaked within 100 ms and then declined to a steady level in a few seconds. Caffeine (1 mmol/l) selectively blocked the transient component of the outward current (ITO) and allowed differentiation of the outward current into two components: ITO and a caffeine resistant background current. The potassium channel blockers TEA (10 mmol/l) and 4-AP (5 mmol/l) produced about 90% suppression of ITO. ITO was identified as a calcium independent potassium current. Analysis of the inactivation and recovery from inactivation of ITO revealed similarities to the A-current first described for molluscan neurones (11) and later for crista terminalis of rabbit heart (4). Being much slower than this current it also bears similarities in its inactivation kinetics to a transient outward current identified in rabbit portal vein (2, 6).