Expression of low voltage-activated Ca2+ channels in Xenopus oocytes

Low-threshold T-type Ca2+ channels are distinctive voltage-operated gates for external Ca2+ entry around a resting membrane potential due to their low voltage activation. These phenomena have already been extensively studied due to their relevance in diverse physiological functions. Recently, three T-type Ca2+ channel alpha (1) subunits were cloned and their biophysical properties were characterized after expression in mammalian expression systems. In this study, alpha (1G) and alpha (1H) low-threshold Ca2+ channels were expressed and characterized in Xenopus oocytes after adding 5 ' and 3 ' untranslated portions of a Xenopus P globin to improve their expression levels. The added portions dramatically enhanced the expression levels of the alpha (1G) and alpha (1H) T-type channels. When currents were recorded in 10 MM Ba2+ as the charge carrier, the activation thresholds were about -60 mV, peak currents appeared at -20 mV, and the reversal potentials were between +40 and +45. The activation time constants were very similar to each other, while the inactivation time constants of the alpha (1G) currents were smaller than those of alpha (1H). Taken together, the electrophysiological properties of the alpha (1G) and alpha (1H) channels expressed in Xenopus oocytes were similar to the previously reported characteristics of low-threshold Ca2+ channel currents.