Resting membrane potential is maximally affected by which ion-

Ans. is 'b' i.e., K+ "RMP is mainly due to difference of concentrations ofK+ ions in ECF and ICF". -- Chaudhari* The cell membrane is selectively permeable. Due to presence of potassium leak channels K+ ions are freely permeable but permeability of Na+ is much less. In the generation of RMP, following sequence of events occur: -i) K+ diffuses out of cell along its concentration gradient (K+ concentration is very high inside the cells and very low in ECF).ii) The diffusion of K+ produces an intracellular negativity (due to non-diffusibleprotein anion in the cells) which is not nullified by the diffusion of Na+ in the opposite direction (membrane is impermeable to Na+) or diffusion of Cl- in same direction (Cl- concentration is already very high in ECF in comparison to ICF).iii) So, intracellular negativity is produced which opposes outward diffusion of K+ and when the equilibrium is reached, the inward force on K+ due to electrical gradient balances outward force on K+ due to concentation gradient.iv) Finally, at equilibrium inner side of cell is negatively charged with respect to outer side, and resting membrane potential is produced.* So, the RMP is principally due to concentration difference (chemical difference) of K+ in ECF and ICF. In neurons, the resting membrane potential is usually about -70 mV, which is close to the equilibrium potential for K+. Here, it is worth noting that RMP is close to the equilibrium potential of K+ but the value of RMP is exactly same as equilibrium potential of Cl~. It is because other ions also diffuse through membrane, though their effect is very little.