Fig. 6. The number of β-subunits but not -subunits in the plasma membrane is dependent on the cell density. HeLa cells with different confluencies (20, 40, 60, 80 and 100%) were prepared. The amount of individual isoforms in the whole cell lysate (A), as well as in the plasma membrane (B), were examined by quantitative immunoblotting as described in Fig. 2. The loading volumes were adjusted based on the total protein amount. The immunoreactive bands were quantified and plotted as described in Fig. 2, with the amount of the 1-subunit at 20% confluence adjusted to 1. Three independent experiments were performed to obtain mean ± s.d. The immunoblotting results are also shown as insets.