|
ICF
|
ECF P
|
|
Pr+
|
5
|
50 2
|
|
Na+
|
50
|
5 1
|
|
K+
|
100
|
200 .01
|
|
Cl-
|
109
|
250 3
|
|
HCO3-
|
?
|
? ?
|
a) He lacked the proper instruments for determining HCO3- concentrations, but was rather certain that no other major ions were present in the ECF and ICF. Can you calculate either concentration for him? (Show all calculations)
b) He measured Em (membrane potential) as -58 mv at 20°C (K = 58 mv at 20°C). What ions could be in a passive equilibrium across the membrane? Why?
Na+ because its electrical potential is the same as the membrane potential, allowing it to flow in and out spontaneously. The electrical potential was calculated by plugging in the ECF as [] out and ICF as [] in, therefore, 58log(5/50)= -58.
c) He determined that the rising phase of the action potential in ltxnsp neurons was due to a sudden hugh increase in PHCO3-. What should be the sign and approximate amplitude of the peak voltage reached by these action potentials? Why?
d) Which ions might be actively transported? Why?
e) Suppose that in other ltxnsp cells the HCO3- in the ICF = 1mM, 10mM in the ECF, and is passively distributed across the membrane. What should be the sign and magnitude of their membrane potential (Em)?