Practice question

Resting membrane potential stability essential for excitability maintained by differential permeability and active ion distribution. Key player is Na+/K+ ATPase, P-type ion pump encoded by ATP1A genes for alpha isoforms, ATP1B for beta, FXYD for gamma regulatory. Catalytic alpha subunit roughly 112 kDa with ten membrane spans contains nucleotide N domain binding ATP, phosphorylation P domain with conserved DKTGTLT aspartate that forms phosphoenzyme intermediate, actuator A domain and transmembrane ion binding pocket coordinating ions with carbonyl oxygens. Cycle Post-Albers: E1 high Na affinity intracellular binding three Na+, phosphorylation to E1P occluding, transition to E2P outward low Na affinity releasing, high K affinity binding two K+, dephosphorylation to E2, return. Electrogenic 3 out 2 in adds minus 3 millivolts directly plus creates gradients enabling K+ leak through Kv and Kir producing minus 70 to minus 90 millivolts. V-type pumps acidify lysosomes, F-type synthesizes ATP, ABC exporters expel drugs. Only P-class Na+/K+ ATPase directly maintains gradients underlying resting potential.