Excitable Membranes
Biol 330

1.  The intracellular and extracellular concentrations of four ions are listed below.  Which of the ions are in equilibrium when the membrane potential is -58 mV ?  Assume 18 C
 
 

Concentration  (mmol/L)
Ion
Intracellular
Extracellular
Cl-
15
150
Mg++
15
1.5
K+
150
15
Na+
15
150
2.  Increasing permeability of a cell membrane to Na+ will have what effect on Vm ??  Explain
 
 

3.  Experimentally increasing the extracellular K+ concentration in skeletal muscle will have what effect on resting membrane potential ?

4.  Lidocaine (novocaine) blocks fast voltage gated channels.  Explain its local anaesthetic properties.
 

5.  In a neuroglial cell culture, the intracellular K+ concentrations and membrane potential are measured to be 100 mM and -58mV, respectively at 18 C.  If the extracellular K+ concentration is doubled by the addition of K+ acetate, calculate the new extracellular K+ concentration.

6.  The ambient temperature of a hydrothermal vent tube worm is 80 degrees C.  The ion concentrations of its cells are unusual:

    Na+ (in) = 10 mM    Na+ (out) = 100mM
    K+  (in)   = 10 mM    K+ (out)  = 5 mM
    Cl- (in)  =  100mM    Cl- (out)  =  10 mM

Calculate the equilibrium potential for each ion.  R= 8.135 J/mol*K,  F= 96,480 J/V*mole,  T ( in degrees K) =  273 + C

7.  What is the resting membrane potential if these worm neurons are equally permeable to both Na+ and K+, but not Cl-  ?