to wrote:I would like to add an NMDA receptor with a realistic calcium permeability as a point process to my model synapse. All NMDA mechanisms I can find use the NONSPECIFIC_CURRENT i, which does not change any intracellular ion concentrations.
If you want to make it a pure Ca current, comment out the
NONSPECIFIC_CURRENT i
and insert
USEION ca READ eca WRITE ica
You'll need to make several other changes, but do them one at a time, testing at
each step to ensure that you're getting what you expected to get. For example,
1. The NEURON block probably declares e as a RANGE variable, but you won't
be using it, so get rid of it.
2. It also probably declares i as a RANGE variable. Change that to ica. Also change i
to ica in the ASSIGNED and BREAKPOINT blocks.
3. You'll need to add
eca (mV)
to the ASSIGNED block.
That's enough to make a synaptic mechanism with a pure Ca current.
If you want to have this be a mixed current, add whatever USEION or
NONSPECIFIC_CURRENT declarations you need, along with their conductances
etc.. If N ionic species are involved, you'll find it more convenient to specify a
total synaptic conductance and have N-1 parameters in the range 0-1 that specify
the fraction that is attributable to each ion (you'll need to bulletproof this by adding
some code to an INITIAL block that ensures that the sum of these parameters is <= 1).
Then the current for each ion will be, for example,
ica = g*fca*(v-eca)
ina = g*fna*(v-ena)
i = g*(1-fca-fna)*(v-e)
where g is governed by whatever kinetics you specified.
How can I plot a NONSPECIFIC_CURRENT i from a point process?
Just make sure that each current component, whether nonspecific or attributable to
a specific ionic species, is declared as a RANGE variable. All RANGE variables are
accessible to hoc.