Question

1. Let us think of the Alaskan King crab living in water that is close to 0 C and even

below 0 C. Why isn’t seawater frozen at 0 C (mechanistically)?

2. Now, how is it that the crab can move and what would happen to the Ek value of the crab were to warm up to room temp (21C)?
3. How would this alter the resting membrane potential of an axon (HOW in relation to the equations you should be familiar with)?

Write out the EK value for 2 different temps and list the values.

Given:

[K] external = 5.3 mM

[K] internal = 168 mM

R=is the universal gas constant and is equal to 8.314 J.K^-1.mol^-1 (Joules per Kelvin per mole).

F=the Faraday's constant and is equal to 96485 C.mol^-1 (Coulombs per mole).

Z=1 (is the valence of the ionic species. For example, z is +1 for Na⁺, +1 for K⁺, +2 for Ca²⁺, -1 for Cl^-, etc. Note that z is unitless.)

T= is the temperature in Kelvin (K = °C + 273.15).

when you plug everything into the Nernst eq. the units will be in Volts

T1= 10 C so Ek =?

T2=20 C so Ek =?

4. Does this make sense with what is measured for resting membrane potentials at these different temperatures?

5. What other factors can account for changes in resting membrane potential with variation in temperature?

Answer 1

-Let us think of the Alaskan King crab living in water that is close to 0 C and even below 0 C. Why isn’t seawater frozen at 0 C (mechanistically)?

Ans: High concentration of salt in seawater lowers its freezing point from 0°C to -2°C (freezingpoint depression). Hence, the ambient temperature should reach a lower point to freeze the seawater.

-Now, how is it that the crab can move and what would happen to the Ek value of the crab were to warm up to room temp (21C)? How would this alter the resting membrane potential of an axon (HOW in relation to the equations you should be familiar with)?

Ans: Crab moves easily in seawater as it is not freezed at 00C. Potassium equilibrium potential (Ek) value of the crab changes from Veq =-81.34mV at 00C to Veq =-87.60mV at 210C, where Veq (equilibrium potential) or Potassium equilibrium potential (Ek). Therefore potassium equilibrium potential (Ek) decreases with increase in temperature.  

One should be familier with Nernst equation and Goldman-Hodgkin-Katz (GHK) equation for membrane potetial (Vm) calculations.

Resting membrane potential of a neuron is about -70 mV (mV=millivolt). At rest, there are relatively more potassium ions (K+) inside than outside. Since the Potassium equilibrium potential (Ek) is less than the restinng potential. Since resting potential of a neuron is about -70 mV (mV=millivolt), the decrease Ek values idicates there will be efflux of K+ ions from the cell.

-Write out the EK value for 2 different temps and list the values.

T1= 10 C so Ek =?

T2=20 C so Ek =?

Does this make sense with what is measured for resting membrane potentials at these different temperatures?

Ans:

T1= 100C so Ek =-84.32mV (milli Volt)

T2=200C so Ek =-87.30mV (milli Volt)

This makes sense that Ek values decrease with increase in temperature. Since resting potential of a neuron is about -70 mV (mV=millivolt), the decrease Ek values idicates there will be efflux of K+ ions from the cell and the rate of K+ ions efflux will be more at high temperature (i.e T2=200C ).

-What other factors can account for changes in resting membrane potential with variation in temperature?

Ans: Differences in ion concentration of the intracellular and extracellular fluids and the relative permeabilities of plasma membrane to different ion species.