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Low-threshold T-type Ca^2+ channels are distinctive voltage-operated gates for external Ca^2+ 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 Ca^2+ channel α_1, subunits were cloned and their biophysical properties were characterized after expression in mammalian expression systems. In this study, α_1G and α_1H low-threshold Ca^2+ channels were expressed and characterized in Xenopus oocytes after adding 5´ and 3´ untranslated portions of a Xenopus β globin to improve their expression levels. The added portions dramatically enhanced the expression levels of the α_1G and α_1H T-type channels. When currents were recorded in 10mM Ba^2- as the charge carrier, the activation thresholds were about -60mV, peak currents appeared at -20mV, 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 α_1G currents were smaller than those of α_1H. Taken together, the electrophysiological properties of the α_1G and α_1H channels expressed in Xenopus oocytes were similar to the previously reported characteristics of low-threshold Ca^2+ channel currents.
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