Bioelectrical Phenomena - Principles of Biomedical Engineering - page 101

(a) Assume the ions in the experiment consist of Na + , Cl − , H + , and OH − , and

calculate the concentration of each ion inside the cartilage sample. The

dissociation constant for water is 10 −14 .

(b) Calculate the concentration of fixed negative charge, G − , inside the

cartilage.

(c) To test the mechanical properties of the cartilage sample, the researchers

placed the cartilage sample between two mechanical plates, and

compressed the sample such that the final sample volume V f was half the

original volume. Assuming that the volume of the salt bath is significantly

larger than the volume of the cartilage sample, the salt concentration in the

bath does not change appreciably after the compression. Calculate the

concentration of ions inside the cartilage sample after compression. Does

the electric potential measured across the cartilage boundary change [per-

sonal communication with Dr. Nada Bowtany, Rutgers University, 2004]?

3.12 Calculate the resting membrane potential for squid giant axon for which the

following data is available.

Species Na + ion K + ion

Intracellular(mM/L) 14 140

Extracellular(mM/L) 142 4

Nernst potential at 37°C (mV) + 61 − 94

A salmon egg deposited in sea water (Na + = 300 mM, K + = 2 mM, Ca 2+ = 3.13 1 mM

and Cl − =

43 mV with an intracel-
lular microelectrode. What can you tell about the composition of the salmon
eggs cytoplasm, if: (a) the membrane is only permeable to potassium (be quan-
titative), and (b) the membrane is only permeable to calcium (be quantitative)?

310 mM), shows a membrane potential of −

3.14 A novel polymer membrane has been formed with the intention of being used

in dialysis. Prior to using, one has to know the membrane permeability. To de-
termine the permeability, an easy technique is to place the membrane between
two chambers. Then one chamber is filled with 0.15M KCl, and the other side
is filled with 0.03M KCl. The measured potential difference across the mem-
brane is 10 mV with side 2 being more positive than side 1. Then the solutions
are replaced by 0.15M NaCl on one side and 0.03M on the other side. Now
the measured potential difference is 40.5 mV with side 1 being more positive
than side 2. What is the P Na /P Cl and P Cl /P K for this membrane?

3.15 Mammalian muscle cytoplasm is composed mainly of Na, K, and Cl. These

same ions dominate the extracellular fluid as well. The following table lists the
composition of cytoplasm and extracellular space of muscle cells:

Na (mM) K (mM) Cl (mM)

Cytoplasm 12 155 4

Extracellular space 145 4 120

(a) What are the Nernst potentials for these ions?