Figure 2.

TTX-S Na_vs are localized to T-tubules. TTX-S Na_vs, including Na_v1.1, Na_v1.3, and Na_v1.6, are located at the T-tubules of CMs where they are thought to participate in the regulation of excitation-contraction coupling. Non-phosphorylated Na_v-β1 subunits are co-localized with TTX-S Na_v-α subunits at the T-tubules where they play roles in calcium signaling and homeostasis. Na_v1.5 is localized at the lateral membrane as well as the ID (Figure 3). At the lateral membrane, Na_v1.5 is complexed with syntrophin and dystrophin. Abbreviations: L-type calcium channel (LTCC), phospholamban (PLB), ryanodine receptor (RyR), sarcoplasmic reticulum Ca²⁺-ATPase (SERCA), sodium-calcium exchanger (NCX), transverse tubules (T-tubule).