1. Archive
2. Vol.51, No.3

Roles of ₁ and ₁/ Subunits Derived from Cardiac L-Type Ca²⁺ Channels on Voltage-Dependent Facilitation Mechanisms

Abstract: Strong depolarization pulses facilitate L-type Ca²⁺ channels in various cell types including cardiac myocytes. The mechanisms underlying prepulse facilitation are controversial with respect to the requirements for channel subunits, cAMP-dependent protein kinase, and additional anchor proteins. The properties of voltage-dependent facilitation of the L-type Ca²⁺ channel was studied in recombinant cardiac ₁ subunits with or without cardiac subunit, expressed in Chinese hamster fibroblast cells. The magnitude of voltage-dependent I_Ba facilitation in the ₁ subunit channel is dependent on the duration of the prepulse as well as on the interval duration between prepulse and test pulse. The characteristics of this facilitation were not affected by coexpression of the subunit. These results indicate that cardiac ₁ subunits exhibit voltage-dependent facilitation because of their own intrinsic structure, independent of any other accessory subunit or additional regulatory proteins, and that cardiac subunits have no essential regulatory role at the onset or continuance of the voltage-dependent facilitation.

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