Question: A rather tame ltxnsp was recently found on Easter Island by a retired neurophysiologist. He reported the following measurements of ECF and ICF concentrations (in millimoles):
|
|
ICF
|
ECF
|
|
Pr+
|
100
|
1
|
|
Na+
|
?
|
?
|
|
K+
|
10
|
100
|
|
Cl-
|
150
|
250
|
|
HCO3-
|
1
|
10
|
a)He lacked the proper instruments for determining Na+ 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 -116 mv at 20°C (K = 58 mv at 20°C). What ions should be in a passive equilibrium across the membrane? Why?
c)He determined that the rising phase of the action potential in ltxnsp neurons was due to a sudden hugh increase in PK. What should be the sign and approximate amplitude of the voltage change of these action potentials? Why?
d)Which ions might be actively transported? Why?
e)Suppose that in other ltxnsp cells the HCO3- in the ICF = 10mM, 1mM in the ECF, and is passively distributed across the membrane. What should be the sign and magnitude of their membrane potential (Em)?