ASER ROTHSTEIN 



95 



inner membrane contains a lipid phase in which are found metabohsm coupled 

 carrier mechanisms for transporting potassium into and sodium out of the 

 cell. The system is represented diagramatically in figure 13. 



H2PO4 



MgHP04 



Mg** <- 



Na* ^ 



EXTRACELLULAR SPACE ^-PERIPHERAL COMPARTMENT OF CELL-> 

 Fig. 13. Scheme of events at the cell surface. 



Mg METAPHOSPHATE 



^-INTERIOR OF CELL-^ 



In the resting cell monovalent cations are in equilibrium across the anion 

 impermeable outer membrane. The equilibrium is readily altered by changing 

 the electrolyte content of the medium. For example, if K+ concentration is 

 raised in the medium, there is a redistribution of ions between the medium 

 and the outer zone of the cell. K+ enters the outer zone and H+ leaves, resulting 

 in an acidification of the medium. This exchange involves only limited numbers 

 of ions however, for the outer zone constitutes only a small fraction of the cell. 



