# [Neuroscience] Re: The relationship between gap junction conductance and coupling coefficient?

r norman via neur-sci%40net.bio.net (by r_s_norman from comcast.net)
Thu Jul 2 06:20:41 EST 2009

```On Wed, 1 Jul 2009 20:44:31 -0700 (PDT), Bill
<connelly.bill from gmail.com> wrote:

>Does anyone know the relationship between gap junction conductance and
>coupling coefficient?
>
>Coupling coefficient is the ratio of the voltage change in cell2 over
>the voltage change in cell1, when current is injected into cell1.
>
>I can see the circuit: Two resistors to ground (Rm of cell 1 and 2),
>linked by the resistance of the gap junction. I can see that as the
>resistance of the gap junction drops to 0, the coupling coefficient
>goes to 1 (Assuming the membrane resistance of the two cells is
>(close) equal, which is a fiar assumption). I can also see, the
>coupling coefficient goes to 0 when there is no coupling between the
>cells.
>
>But is it possible to convert the coupling coefficent to a gap
>junction conductance?

The coupling coefficient is simply Rm2/(Rg + Rm2), the membrane
resistance  of cells 2 divided by the total of the gap resistance and
the membrane resistance.  If you know Rm2 you can do what you ask
since the junction conductance is simply 1/Rg.  If you don't know it,
you can't.

```