Specify basic channel properties

Step 2. Specify the channel's basic properties

Clicking on the Properties button reveals a menu that allows us to specify the basic properties of the channel.

Let's review the items in this menu.

The Properties Menu

Channel Name
Like the "suffix" in an NMODL-specified channel. Changing the name of the channel will change the suffix.
Selective for Ion . . .
Similar to the USEION statement. Your initial choices are NonSpecific, na, k, and Create a new type. If you choose Create a new type, up pops a little window with an edit field so you can type the name of the new ion followed by a space and then a number for its charge (this is analogous to NMODL's USEION x VALENCE n syntax).
       Example: to create a chloride current, type cl -1
After you create a new type of ion, it is automatically available at the hoc level and integrated into all relevant GUI tools (including this one!).

Ohmic i=g*(v-e)
   and
Goldman-Hodgkin-Katz
Specify whether the current-voltage relationship is instantaneously linear ("ohmic") or governed by the nonlinear GHK equation. A checkmark indicates which option has been selected ; the default is "ohmic."
Default gmax (or pmax)
Used to specify maximum conductance of an ohmic channel, or permeability of a GHK channel.
HH sodium channel
   and
HH potassium channel
Shortcuts for quickly configuring the Channel Builder to model one of the classical squid axon active currents--a good starting point for many new channel models.
Clone channel type
Spawns another Channel builder whose specifications are identical to the present one, with a single exception : an automatically generated "index" is appended to the "channel name." so that the two mechanisms won't interfere with each other. This is a good way to create a family of related channels.
Copy gates from
Imports gate properties from another Channel builder. This is an alternative way to create a family of related channels.
Text to stdout
Prints a concise description of the channel to stdout, i.e. the same window as the oc> prompt.
Gate Constructor
Brings up a tool for specifying gate properties.

Let's use the items in the Properties menu to fix the channel's name, ion, and default conductance and equilibrium potential.

A. Specify the channel's name.

Select
Properties / Channel Name
and a window with an edit field appears.

Click inside the edit field and change the name as desired (for this example I decided on myna).

Now click on the Accept button, or press the Enter key on the keyboard. The window will disappear and the new name will appear in the Channel Builder.

B. Specify the channel's ion.

Select
Properties / Selective for Ion . . .
and a secondary menu appears that lists the available ions.

From the list of available ions, choose na

After releasing the mouse button, notice the changes in the top panel of the Channel Builder :

"NonSpecific ohmic ion current" is now "na ohmic ion current"
"i_myna = g_myna * (v - e_myna)" is now "ina = g_myna * (v - ena)"
"Default gmax = 0 (S/cm2) e = 0 (mV)" is now "Default gmax = 0 (S/cm2)"

C. Specify the channel's default conductance and equilibrium potential.

Select
Properties / Default gmax
This brings up a "Default gmax" window that we can use to specify the default conductance.

For this example we need a value of 0.12 S/cm2.

The sodium equilibrium potential ena already has a default value, so we don't have to do anything about it.

What if our mechanism used some new ion x whose equilibrium potential ex is not already known to NEURON?

The Channel Builder would automatically assign ex a default value of 0.
The "Default gmax" window would offer a second row with widgets and and a numeric field so we could specify a nonzero value for ex.

Now that we have specified the basic properties of this channel, here's what the Channel Builder looks like :

Time to save everything to a session file! I called mine hhchannel.ses

Next we will specify the gating of our new channel.

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