A βIV-spectrin/CaMKII signaling complex is essential for membrane excitability in mice

Ion channel function is fundamental to the existence oflife. In metazoans, the coordinate activities of voltagegated Na + channels underlie cellular excitability and control neuronal communication, cardiac excitation-contraction coupling, and skeletal muscle function. However, despite decades of research and linkage of Na + channel dysfunction with arrhythmia, epilepsy, and myotonia, little progress has been made toward understanding the fundamental processes that regulate this family ofproteins. Here, we have identified β IV -spectrin as a multifunctional regulatory platform for Na + channels in mice. We found that β IV -spectrin targeted critical structural and regulatory proteins to excitable membranes in the heart and brain. Animal models harboring mutant β IV -spectrin alleles displayed aberrant cellular excitability and whole animal physiology. Moreover, we identified a regulatory mechanism for Na + channels, via direct phosphorylation by β IV -spectrin-targeted calcium/calmodulin-dependent kinase II (CaMKII). Collectively, our data define an unexpected but indispensable molecular platform that determines membrane excitability in the mouse heart and brain.