Practice question

Intracellular ion composition is highly asymmetric relative to extracellular fluid actively maintained using ATP to support excitability volume and enzyme function. In most mammalian cells at rest dominant intracellular cation is potassium one thirty to one forty millimolar inside versus four to five outside ten to thirtyfold gradient while sodium inverse ten to fifteen inside versus one forty five outside chloride four to twenty inside versus one ten outside bicarbonate ten inside versus twenty five outside free calcium extremely low one hundred nanomolar inside versus one point two millimolar outside twelve thousandfold plus magnesium half millimolar free. Asymmetry established primarily by continuous Na+/K+ ATPase exporting three sodium importing two potassium generating chemical and electrical gradients plus NKCC importing K+, chloride and sodium channels like Kir Kir4.1 leaking potassium to set resting potential close to potassium Nernst minus ninety millivolts. High potassium required for sixty S ribosomal peptidyl transferase pyruvate kinase maintaining negative potential counterbalancing anionic proteins buffering pH via K+/H+ exchange preventing apoptosis. Reduction triggers caspase activation and cell shrinkage during apoptosis.