K_Ca2 channels are not expressed in wild type HEK 293 cells.

<p>A Immunostaining of HEK 293 cells transiently transfected with GFP and K_Ca2.2 (a,b,c) or K_Ca2.3 (d,e,f). GFP expressing cells are visible in a and d. Comparison with the brightfield images in c and f shows that only a proportion of the cells were transfected. Staining for K_Ca2 channels is shown in b and e where a signal is only visible in cells also expressing GFP. The scale bars indicate 10 µm. B Whole cell currents from a wild type HEK 293 cell recorded using a calcium containing internal solution before (▪) and after exposure to 10 nM apamin (•). The endogenous current is not inhibited. C Current voltage relationship for recordings in B. D Binding of ¹²⁵I-apamin to wild type, K_Ca2.2 and K_Ca2.3 expressing HEK 293 cells. Cells were incubated with 30 pM ¹²⁵I apamin in the absence (T) or presence (N.S.) of 100 nM UCL 1848. There is no significant binding in wild type cells. In contrast, total binding is much higher in cells expressing K_Ca2 expressing cells and is almost completely inhibited by UCL 1848.