The use of small interfering RNA to elucidate the activity and function of ion channel genes in an intact tissue

Small interfering RNA (siRNA) directs the targeted destruction of mRNA encoding a specific protein, in a process known as RNA interference (RNAi). This stops translation of the targeted mRNA into protein, effectively silencing the gene. RNAi is a recent discovery, identified in mammalian cells in 2001, but it has rapidly advanced into a practical technique and is being used increasingly to investigate mammalian gene function. Tools are available to induce RNAi in cell lines, intact tissue preparations and even in vivo. Depending on the method used, loss of gene expression may be transient or sustained, enabling a wide range of functions to be investigated. RNAi therefore offers a powerful technique that can be used to produce targeted knockout of ion channel genes in mammalian cells. Its applications potentially include identification of ion channel function in health and disease, identification of novel channel genes and drug target validation. This paper outlines our current understanding of siRNA and the experimental requirements for producing efficient RNAi and gene silencing. Effective RNAi requires an appropriate siRNA sequence to be designed and an efficient method for delivering the siRNA to the cells of interest. Since not all potential siRNA sequences are effective, it is also important to verify the loss of gene expression by measuring the level of channel protein remaining. Limitations of the methods available for delivering siRNA are one of the main obstacles to producing efficient RNAi, especially in intact tissue preparations. Here we describe an in vitro method for targeted RNAi against the TASK-1 potassium channel gene in an isolated vascular preparation, using a DNA construct to direct the expression of siRNA, along with a non-viral method for transfecting cells within the vessel. Successful silencing of the TASK-1 gene is verified by immunostaining with an antibody directed against the TASK-1 protein.