Differential plasma membrane targeting of voltage-dependent calcium channel subunits expressed in a polarized epithelial cell line

1. Voltage-dependent calcium channels (VDCCs) show a highly non-uniform dis tribution in many cell types, including neurons and other polarized secreto ry cells. We have examined whether this can be mimicked in a polarized epit helial cell line (Madin-Darby canine kidney), which has been used extensive ly to study the targeting of proteins. 2. We expressed the VDCC alpha 1A, alpha 1B or alpha 1C subunits either alo ne or in combination with accessory subunits alpha 2-delta and the differen t beta subunits, and examined their localization immunocytochemically. An a lpha 1 subunit was only targeted to the plasma membrane if co-expressed wit h the accessory subunits. 3. The combination alpha 1C/alpha 2-delta and all beta subunits was always localized predominantly to the basolateral membrane. It has been suggested that this is equivalent to somatodendritic targeting in neurons. 4. In contrast, the alpha 1B subunit was expressed at the apical membrane w ith all the accessory subunit combinations, by 24 h after microinjection. T his membrane destination shows some parallels with axonal targeting in neur ons. 5. The alpha 1A subunit was consistently observed at the apical membrane in the combinations alpha 1A/alpha 2-delta/beta 1b or beta 4. In contrast, wh en co-expressed with alpha 2-delta/beta 2a, alpha 1A w as clearly targeted to the basolateral membrane. 6. In conclusion, the VDCC alpha 1 subunit appears to be the primary determ inant for targeting the VDCC complex, but the beta subunit can modify this destination, particularly for alpha 1A.