The values of the ionic conductances for excitatory neurotransmitters can be found from the paper published by A. L. Hodgkin and A.F. Huxley. Are the values same for inhibitory neurotransmitters? Is yes, then what is the difference?
Hi Bijeet,
I think the values of ionic conductances are the same. The only difference will be at postsynaptic level. At an excitatory synapse, neurotransmitter opens channels in the postsynaptic membrane that are permeable to cations, principally Na+ and K+. On the contrary, the direction of IEPSP is outward; an outward Cl− current represents an influx of the negatively charged Cl−, which will hyperpolarize the cell. Another possibility is that the inhibitory synapse channel is permeable to K+, with a Nernst potential of −90 mV. An increased permeability to K+ can bring the membrane potential close to the Nernst potential for K+ and thus hyperpolarize the cell.
The ionic conductance given in Hodgin & Huxley paper are measured during resting membrane potential or spike. If your are intersting in the conductance of GABA LGIC, you need to know the channel subunit composition in order to find the channel conductance. In a more general point of view GABA receptor are permeable to Cl- and HCO3-, therefore you need to control them in both your pipet and extracellular solution.
The conductance not change, only if you change the cannel in deep, maybe you ask of driver forcé of the ion in the inhibotry condition and in these case you must to take atention at you solution. remember, the mass of ion moved when a cannel are open is very low, but the cahrge are bigger, take atention to nerst potential
GABA-A (inhibitory) postsynaptic receptors are ionotropic and primarily conduct chloride (Cl-) ions. Under most conditions the chloride equilibrium potential will be close to the membrane resting potential, ER; when ER = ECl-there will be no net ion flux through the GABA-A channel in the presence of the inhibitory synaptic transmitter. If ER is more negative than ECl- the driving force on the chloride ions will lead to a net efflux of chloride during the action of the inhibitory transmitter, generating depolarizing IPSPs. If ER is more positive than ECl- there will be a net influx through the channel during transmitter action, and th IPSPs will be hyperpolarizing.
Hi Bijeet,
As Pascal mentioned, GABAA receptors are permeable to both Cl- and HCO3- ions, and their conductances vary considerably based on subunit composition. To get a sense of the heterogeneity that's out there in this population of receptors, I'd recommend checking out:
http://www.jneurosci.org/content/19/8/2960.full.pdf
You may find figure 6 to be particularly informative with regards to your question.
One caveat, though, GABAB receptors are GPCRs, with G-proteins that typically activate K+ conductances (although, there are of course other targets as well). If you plan to model or study ion-specific conductances in your system of interest, it's well worth considering before hand which of these two channel types carry the bulk of GABA-mediated IPSPs.
http://www.jneurosci.org/content/19/8/2960.full.pdf