All cells contain ion pumps that use the energy of ATP hydrolysis to pump ions across the plasma membrane. These pumps create an electrochemical gradient across the plasma membrane that is used to power other processes at the plasma membrane, including some transport processes. In animal cells, the main ion pump is the sodium-potassium pump.
-OUTSIDE CELL B. ([Na+]low, [K+]high) or ([Na+]high,[K+]low)
C. (excess + charge) or (excess - charge)
-(BETWEEN) A. (3[Na+]v,2[K+]^)，（2[Na+]^,3[K+]v), (3[Na+]^,2[K+]v)
-INSIDE CELL D. ([Na+]low,[K+]high) or ([Na+]high,[K+]low)
E. (excess + charge) or (excess - charge)