Active transport.
<P>
   The  sodium-potassium  pump  maintains  high  concentrations  of  Na^+
   outside  the cell and K^+ inside the cell, against their concentration
   gradients.
<P>
<Li> 3 cytoplasmic Na^+ bind to the pump.
<Li> ATP donates a phosphate group for energy.
<Li> The protein changes its shape, expelling Na^+ to the outside.
<Li> 2 extracellular K^+ bind to the pump, releasing the phosphate.
<Li> The pump resumes its original shape.
<Li> K^+ is released inside.
<P>
   Review:  <A ClAsS=MID Href="../../../med/Vid/Johnson6e/ch05/sodium_potassium_exchange_pump.swf" oNClick="popurlt('../../../../med/Vid/Johnson6e/ch05/sodium_potassium_exchange_pump.swf');txtcolor('pump1','gray');return false;" Id=pump1><iMg sRc="/images/shockwave.gif" aLt='' boRDer=0></A>