A). The Na+
-Ca2+ antiporter (NCX) transports Ca2+ out of the cell against its concentration
gradient through transporting Na+ into the cell along its concentration gradient. With NCX, the
inward transport of 3 Na+
ion drives the outward transport of 1 Ca2+ ion. Typical Na+
, Ca2+
concentrations and membrane potential are indicated below. With this information, calculate
how low a Ca2+ concentration can be generated (in principle) inside the cell solely by NCX?
Utilize the same working we encountered in class for SGLT1, but consider that NCX is an
antiporter, whereas SGLT1 is a symporter. Thus the maximal electrochemical gradient of Ca2+
will be opposite that of glucose. (6)
B) Describe why NCX transport of 3 Na+
ion for each Ca2+ ion is necessary, rather than
transporting a single Na+
ion for each Ca2+ ion. (2)
C) Briefly describe one reason why minimizing intra-cellular Ca2+ may be useful for a cell’s
function? (2)
The electrical and chemical potential is: ∆?? = ???? [?]?
[?]?
+ ?????
The following may also be helpful: ??
???
?? [?]?
[?]?
=
61.5??
??
???10
[?]?
[?]?
Extracellular Na+ concentration is 140mM, intracellular Na+ concentration is 12mM, extracellular
Ca2+ concentration 2.5mM, and the resting membrane potential is -65mV.