Electrical equivalent circuit for the plasma membrane of a rat ventricular cell. Figure 2: Cm,TT: membrane capacitance of the junctional SL membrane coupled with the dyadic space; Cm,SL: membrane capacitance of the uncoupled free SL membrane; Currents through the uncoupled free SL membrane are (a) ICa,L,SL: L-type calcium current, (b) INa,SL: sodium current through the DHPR channel, (c) ICs,SL: cesium current through the DHPR channel, (d) INaC a,SL: sodium-calcium exchanger current, (e) INaCs,SL: sodium-cesium exchanger current, (f) I
: calcium pump current, (g) INa,b: background sodium current; Currents through the junctional SL membrane coupled with a dyadic space are (h) ICa,L,TT: L-type calcium current; (i) INa,TT: sodium current through the DHPR channel, (j) ICs,TT: cesium current through the DHPR channel, (k) INaCa,TT: sodium-calcium exchanger current, (l) INaCs,TT: sodium-cesium exchanger current; V
: potential in external medium; V
: intracellular potential; The coupling resistance between the surface sarcolemma and the transverse tubules being very small is neglected in our model hence V
: common transmembrane potential across both uncoupled and coupled membranes.