MadSci Network: Biochemistry

Re: What is the relationship between Ca/P and K/Na ?

Date: Fri Mar 12 08:02:46 1999
Posted By: Michael Maguire, Faculty,Case Western Reserve Univ.
Area of science: Biochemistry
ID: 920987305.Bc

I assume that lymphatic fluid you mean the small amount of extracellular 
plasma/fluid that surrounds cells within the lymphatic drainage system.

Regardless, the pH of any fluid has nothing directly to do with Ca/P or 
Na/K.  pH is of course the negative log of the proton concentration, 
[H+].  None of these ions would have a major effect on pH, nor would their 
ratios.  The only possible exception would be phosphate, P, which, if 
present if high concentrations, would tend to decrease pH by binding 
available H+.  But, no extracellular fluid I am aware of has any 
significant concentration of phosphate at any time.

In most cells in eukaryotes, particularly in mammals, the amount of 
intracellular Na+ is about 5-10 mM while the intracellular K+ is 110-150 
mM, depending on the cell type.  There are exceptions, but relatively 
uncommon in mammals.  Thus the K/Na ratio would be 10-30.  It does not 
change markedly at any time, unless the cell is dying.

I am not sure what you mean by a "potassium pump."  The phrase "sodium 
pump" normally refers to an enzyme called Na+,K+-ATPase.  This is an 
enzyme in the plasma membrane of most cells that is the primary mechanism 
for maintaining the membrane potential and the ratio of Na and K across 
the membrane.  It uses the energy from ATP to pump 3 Na ions out (cytosol 
to extracellular space) and then, in the second part of the cycle, allow 2 
K ion back in.  This creates a charge imbalance of 1 plus charge per cycle 
thus making the inside of the cell more negative with respect to the 
outside of the cell.  This compensates for entry of Na by a variety of 
other transport systems, which use the electrochemical energy inherent in 
the Na gradient across the plasma membrane (150 mM outside, 5-10 mM 
inside, plus the negative inside membrane potential) to pump other ions, 
sugars and other substances out of or into the cell.

There is no "potassium pump".  Potassium normally enters and exits through 
K+ channels or other similar transport systems such as the Na,K-ATPase.  
Since the Na,K-ATPase does pump K into the cell, I suppose it could be 
called a "potassium pump", but this is not really the important 
physiological function of this enzyme, the sodium pumping is.

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