Roles of alpha(1) and alpha(1)/beta subunits derived from cardiac L-type Ca2+ channels on voltage-dependent facilitation mechanisms

Strong depolarization pulses facilitate L-type Ca2+ channels in various cel l types including cardiac myocytes. The mechanisms underlying prepulse faci litation are controversial with respect to the requirements for channel sub units, cAMP-dependent protein kinase, and additional anchor proteins. The p roperties of voltage-dependent facilitation of the L-type Ca2+ channel was studied in recombinant cardiac oil subunits with or without cardiac beta su bunit, expressed in Chinese hamster fibroblast cells. The magnitude of volt age-dependent I-Ba facilitation in the oil subunit channel is dependent on the duration of the prepulse as well as on the interval duration between pr epulse and test pulse. The characteristics of this facilitation were not af fected by coexpression of the beta subunit, These results indicate that car diac oil subunits exhibit voltage-dependent facilitation because of their o wn intrinsic structure, independent of any other accessory subunit or addit ional regulatory proteins, and that cardiac beta subunits have no essential regulatory role at the onset or continuance of the voltage-dependent facil itation.