After raising Ko, the measured value of vm approximates that predicated by the Nernst equation for Km(equilibrium potential). The measured values are slightly less negative than those predicted by Nernst equation because of the small but finite gN IIII External K concentration(mM) Figure 17-3 The Vm of a cardiac muscle fiber varies inversely with the K concentration of the external medium. The oblique blue line represents the E predicted by y the Nernst equationAfter raising [K]o, the measured value of Vm approximates that predicated by the Nernst equeation for Km (equilibrium potential). The measured values are slightly less negative than those predicted by Nernst equation because of the small but finite gNa