When hydrogen ions (H+

) enter a cell they quickly bind to various proteins, called buffers. This is so that the cell can control its pH precisely.

Interestingly, the same is true of Ca2+

ions, whose concentration also needs to be controlled carefully, but not true for Na+ or K+

ions.

If we assume that the reaction between H+

and its buffers is very fast, we can show that b =

bt h K + h

, where b is the concentration of H+

bound to buffers (in units of mM), bt is the total concentration of buffer (including all the buffer proteins that are not yet bound to H+

), h = [H

+

] (in units of mM) and K is a constant.

a. What are the units of K and bt?

b. Can bt or K be negative? Explain.

c. What is the physiological interpretation of bt − b?

d. How is db/dt related to dh/dt?

e. Suppose that bt is much bigger than K, but h is much less than K. Which increases more quickly, b or h? What are the physiological consequences of this? That is, explain how this shows that the buffer is controlling the pH.