Figure 4. CaM is required for surface expression.

Immunocytochemistry of COS cells transfected with the indicated combinations of SK2:64/67, CaM, and a GFP expression plasmid. SK2:64/67 harbours three tandem copies of the myc epitope in the external loop between transmembrane domains 3 and 4. For each panel, transfected cells were visualized by expression of GFP (G; left), channel protein was detected with an anti-myc mouse monoclonal antibody and visualized by Texas Red-conjugated horse antimouse secondary antibody (R; middle) and the signals were merged (M; right). In each case, cells were examined either without (–) or with (+) the membrane permeabilization. Top, SK2:64/67 was not detected on the cell surface (–) but channel protein was detected inside permeablized cells (+). Middle, SK2:64/67 was detected on the cell surface (–) as well as inside the cell (+) when transfected with wild-type CaM or bottom, the Ca²⁺-independent CaM mutant, CaM1,2,3,4. (Reproduced with permission from: Lee et al. 2003.)