<prompt> In muscle cells, resting membrane potential is equal to the isoelectric potential ofNaCl-KMg  <response>: The isoelectric potential of Cl- is -70mV and of K is -90mV.According to Ganong and Principles of Medical Physiology, the actual measured RMP of a nerve fibre is -70mV rather than the calculated value of -90mV. So in nerve fibres, the RMP is equal to or closer to the isoelectric potential of Cl-.Whereas in muscle cells, the RMP is -90mV, which is equal to the isoelectric potential of K. 