Single-channel analysis of a cloned human heart L-type Ca²⁺ channel α₁ subunit and the effects of a cardiac β subunit

Macroscopic and single-channel properties of a cloned human heart L-type Ca²⁺ channel α₁ subunit expressed in Xenopus oocytes were studied and the effects of a cardiac β subunit were evaluated. The α₁ subunit expressed current with much slower activation and inactivation kinetics than native cells. The β subunit increased the current amplitude and accelerated both activation and inactivation rates. Single-channel analysis revealed that the β subunit increased the probability of channel opening and shifted the voltage-dependence to more negative potentials without affecting conductance or open time. The data suggest that the β subunit modulates macroscopic current by increasing the probability of channel opening and shifting the voltage-dependence of the channel.