1.
(12 pts) Remember the giant squid recorded Alices
Scientific Journal? These LGW
(Looking Glass World) predators have complex muscular and nervous systems, and
their excitatory cells (and surrounding fluids) exhibit the ionic
concentrations (in mM) listed in the Table below. Trans Looking Glass monovalent ions differ from ours, and the
ones commonly found in organisms on the other side are represented in the Table
below:
| Ion: | M+ | N+ | O- |
| Inside cells - | 260 | 4 | 34 |
| Outside cells - | 10 | 290 | 300 |
Patch-clamping
measurements indicate stimulated
squid nerve and muscle cells exhibit striking changes in membrane potential as
indicated below; these changes are called LAPs (or Looking-Glass Action
Potentials). The resting membrane
potential is +88 mV, and the log values for the ratio of the inorganic ions are
indicated along the side. Alice found
the temperature over there a uniform temperature of 298 o K
|
|
Logs of Concentration Ratios:
[M+]in/[M+]out = 1.41
[M+]out/[M+]in = -1.41
[N+]in/[N+]out = -1.86
[N+]out/[N+]in: = 1.86
[O-]in/[O-]out = -0.95 [O-]out/[O-]in = 0.95 Answer
all the following questions, showing all relevant calculations. |
A.
(4 pts) How is the resting potential
likely generated in these cells?
Briefly explain the basis for your answer.
B.
(4 pts) Describe the LAP and what
changes in membrane properties likely produce its various features.
C.
(4 pts) LAPs may be stimulated in the
lab by decreasing the resting potential electronically. How is a LAP likely stimulated in situ
when, for example, a squid motor nerve stimulates a muscle fiber?