We studied the postulated involvement of the protein kinase C beta 1 (PKC beta 1) isoform in the regulation of endothelial permeability using human dermal microvascular endothelial cell line (HMEC-1). We overexpressed the recombinant PKC beta 1 gene via retroviral-mediated transduction in these cells. PKC beta 1 gene transfer was stable, and PKC beta 1 protein production was persistent for at least 1 month posttransduction. Addition of 2 x 10(-9) M and 2 x 10(-8) M phorbol 12-myristate 13-acetate (PMA) to the control (nontransduced) HMEC-1 cells increased the transendothelial 125I-albumin clearance rate (an index of endothelial permeability) from 2.5 +/- 0.2 x 10(-2) microliters/min to 5.4 +/- 1.2 x 10(-2) microliters/min and 16.8 +/- 3.1 x 10(-2) microliters/min, respectively. However, addition of 2 x 10(-9) M PMA to PKC beta 1-overexpressing HMEC-1 cells produced a maximal increase in the transendothelial 125I-albumin clearance rate of 15.9 +/- 2.0 x 10(-2) microliters/min. Challenge of these cells with 2 x 10(-8) M PMA did not further augment the increase in permeability. Activation with PMA was associated with the translocation of the PKC beta 1 from the cytosol to the membrane. These data show that PKC beta 1 overexpression augments the increase in endothelial permeability in response to PKC activation, suggesting an important function for the PKC beta 1 isoform in the regulation of endothelial barrier.