Different Densities of Na-Ca Exchange Current in T-Tubular and Surface Membranes and Their Impact on Cellular Activity in a Model of Rat Ventricular Cardiomyocyte

Figure 4

Ca²⁺ transferred by individual ion flux pathways across the cellular membrane ((a); surface, white bars; t-tubules, black bars), through the cytosol (b), and across the junctional SR membrane (c) during one steady-state cycle (1 Hz) at different values of (0.48, 0.78, and 0.93). The columns marked Ca,s, Cab,s, NaCa,s, pCa,s and Ca,t, Cab,t, NaCa,t, pCa,t show the amounts of Ca²⁺ (in amol) transferred by L-type Ca current (, ), background Ca current (, ), Na-Ca exchange current (, ), and Ca pump current (, ) across the surface and t-tubular membrane, respectively. The columns marked and represent the related net amounts of Ca²⁺ transferred across each membrane separately. The total sarcolemmal Ca²⁺ entry during the cycle equals the total extrusion and is similar at all three values of (~124 amol). The grey columns denote the amounts of Ca²⁺ that enter cytosol through the surface and t-tubular subsarcolemmal spaces (, ), that are sequestered from the cytosol by SR (), and that are released from the junctional pools of SR at the surface and t-tubular membranes (, , in total ). At any steady state, .

(a)

(b)

(c)