Expression of ABC-type transport proteins in human platelets.

We have identified the ATP-binding cassette (ABC) transporter ABCC4 as an active constituent of mediator-storing granules in human platelets. In addition to multidrug resistance protein 4, other ABC-type transport proteins may contribute to platelet secretory function as well as determine intended or adverse effects of drugs. Here, we provide a comprehensive expression profiling of ABC transporters in human platelets based on a novel screening approach by combining the TaqMan low-density array RNA screening platform with a recently developed liquid chromatography/mass spectrometry (MS)/MS method for the simultaneous detection of membrane proteins. Transcripts of 25 ABC transporters were detected and showed differential expression compared with megakaryocytic progenitor cells. On the protein level ABCA7, ABCB4, ABCC1, ABCC3 and ABCC4 were identified by liquid chromatography/MS/MS and localized by immunofluorescence microscopy. Their functions may be related to glutathione and lipid homeostasis, secretion of lipid mediators, cell protection as well as drug transport.