Hyponatremia has no effect on the RMP (resting membrane potential) because
Resting membrane potential depends on the concentration of potassium ion and not on sodium ion. (REF TEXTBOOK OF MEDICAL PHYSIOLOGY GEETHA N 2 EDITION, 23)
The cell membrane is impermeable to Na+
ECF Na+ concentration is high
Intracellular K+ concentration is high
Equilibrium potential for Na+ is +60 mV
General physiology