The role of endogenous beta subunits of the L-type Ca channel in native cardiac ventricular myocytes is unclear. We have therefore investigated the effect of inhibiting beta subunit expression in rat myocytes, by culturing isolated myocytes for 24 It with either antisense oligonucleotide against the beta subunit or with scrambled oligonucleotide (control). alpha(1) subunit expression and distribution were then determined by immunolabeling, and L-type Ca current measured using the whole cell patch-clamp technique. Cells treated with antisense showed increased perinuclear staining for alpha(1), decreased Ca current amplitude and a small rightward shift of the activation curve and the I-V relation, with no significant effect on inactivation. These data suggest that endogenous beta subunits in native cardiac myocytes help to traffic the alpha(1), subunit to the cell membrane and thus play a major role in determining Ca current amplitude. (c) 2006 Elsevier Inc. All rights reserved.