1-Sensitive and Self-Sensitive Cells (13 Oct) cell electrophysiology (3-…
1-Sensitive and Self-Sensitive Cells (13 Oct)
1- diffusion and mov. of charged molec.
across the memb.
ionic basis of memb. potentials
steady state memb. potential
roles of ion channels in excitable cells,
nerve cells and muscle cells
electrical signalling in specific cells
2- expression of ion channels and
memb. potentials are imp. in all cells
reason: functions regulated by
seperation of ions across memb.
AND mov. across memb.
they provide seperation of positive and negative
charge across memb.
cause diffusion of ions across memb.
structural changes in various proteins
change relative permeability of the memb.
large impact on the properties of the cells
ions are the most abundant dissolved solutes
can influence the osmolarity of the solution
eg. increase or decrease in Ca or K :
main ions in intra cellular and extra cellular fluid
change the osmotic equil.
dramatic chenges in cell size
3- mov. of charegd ions have
control mechanism over a number of functions in the body
secretion or absorption in apithelial cells
fundamental for sensory signalling
muscles >>>ions involed in triggering
the contraction and force production is Ca
release of Ca is mediated by actual potentials
of Na and K ions across the memb.
intracellular enzyme cascade
regular gene expression, cell growth and death
conc. of ions and presence of ion channells is impor. in regulation
mov. of ions critical for various func
4- how does the electrical properties of the cell (membrane potentials) influence the
mov. of these ions and the permeability
of the membrane for that particular ion
expression of ion channels is impo because positively charged ions can't diffuse through the lipid bilayer
drive the movement of one solute from one side of the mem. to the other
charge of the ion
have electrical force to diffuse across memb.
negati. chaged ions are repelled by negative charge inside the cell
what is the electrical properties of the cell on either side
with respect to the charge of the ion
5- a bulk solution is
always electrically neutral
if we consider extracellular and intracellular together
built of positive charge of the extra cellular
balanced by the negative charge on the inside of the memb
whole solution is electriclly balanced... this is memb potentialn we can measure it
2 recording electrodes
in the same solution : detecting the same composition of positive and neg. ions ... no voltage no difference in charge being detected...
one electrode in the intracellular solution
reference elec outside the cell
we can record positive and negative charge across memb.
record a mem. potential of about -60 mvolt
7- small number of charges generates large voltage
establishment of memb. potential and changes in memb. potential. during electrical signalling
comes about by the diffusion of small number of ionsp
diagram shows that the cons. grad. is huge but
the number of ions that you need to diffuse across the memb. to establish the membrane potential of -90 mv is just 6 ions small
the no/ of ions that move that develop that memb. potential P are incredibly small inrelation to total concentration of those ions
electrical signals or properties esatablished without significant changes in the concentration gradient
membrane is permeable to K+ why not K+ continue to diffuse down its conc. gradient to its ultimate entropy to have equal conc. of K+ on either side?
each time K+ diffuses out:
leaves behind a negative charge inside the cell and posiveve charge outside
establishing diffusion potential
introduce another force that acts on that ion
electrical force or electrical potential
tries to keep ions in the cell and
acts to pull K+ into the cell
these forces are in opposing directions
K+ will continue to diffuse out until equilibrium situ.
1 more item...
6- how memb. potential
become established in the first place
for diffus. we need conc. grad.
conc. of K+ inside the cell is much higher than conc.
of K+ outside the cell
conc. gradient of Na is in opposite direction
each of positively charged ions is balanced by an anion...
so the solution is electrically neutral
we need membrane that is permeable to the solute
memb. of our cells relatively more permeable to K+ than other solutes
it can diffuse down its conc. gradient.
ion channels are selective for K+>>> will let K+ diff. out
leave behind large negatively charged molec. inside the cell
that cant diff across
K+ diff. down its conc. grad. to the outside
excess negatively charged left behind in the intracellular cell a>>> that is what builds up the separation of charge and we can measure that as voltage
selective permeabilty of memb. to K+
allows diff. of K+ down its conc. grad.
estalishes separation of charge to that memb. potential
8- key points about diffusion potentials
seperation of charge requires a
selectively permeable memb.
allows move. of ions down its conc. grad.
sign of the voltage depends on charge
on the diffusing ion
diffusion of K+ out of the cell
inside of the cell more negative
diff. of cloride ion out of the cell: anion
positive charge inside the cell
we need to consider the direction
(into or out of the cell)
and the charge of that ion
-ve charged ion moving into the cell
have the same effect as +ve charged ion moving out of the cell
magnitude of voltage depends on the conc. grad.
larger conc. grad.
larger chemical driving force
need to develop a sufficient electrical force to counteract that conc. grad to reach eq.
diffu. potentials don't directly rely on metabolic energy
we dont require any direct pumping of these ions across the memb. for the diffusion potential to occur
but it requires an already stablished conc. gradient
electrical charge is generated by passive diffusion down that conc. grad.
we can calculate the memb potential that need to be at for that ion to be at eq. using the Nernst eq.