### Intracellular potassium depletion

Posted:

**Sun Sep 04, 2016 12:26 am**I want to simulate intracellular K+ depletion by outward K+ current in a semi-sphere space with radius of 1 uM and volume of 2.1 um3. The outward K+ current is set to be 5 nA with duration of 3 ms, which equals to an efflux of 1.55e-16 mole of K+. Thus the intracellular K+ should be reduced by 74 mM. I wrote the following mechanism to simulate change of intracellular K+ by this outward K+ current. The extracellular [K+] is assumed to be constant.

Simulation using this mechanism shows that with 160 mM K+ on both sides the intracellular [K+] was only reduced by less than 5 mM (160 -> 155.5 mM) by above K+ current in a single compartment cell with L and diam of 1.386 um.

Please help.

P.S. Here is the screenshot of the simulation.

Code: Select all

```
COMMENT
Modified from the code posted at
https://www.neuron.yale.edu/phpBB/viewtopic.php?f=16&t=1938&p=7158&hilit=intracellular+concentration#p7158
ENDCOMMENT
NEURON {
SUFFIX kiacc
USEION k READ ik WRITE ki,ko
RANGE ki0,ko0
}
UNITS {
(mV) = (millivolt)
(mA) = (milliamp)
FARADAY = (faraday) (coulombs)
(molar) = (1/liter)
(mM) = (millimolar)
}
PARAMETER {
ki0 = 160 (mM) : Initial K conc within the section
ko0 = 160 (mM) : Initial K conc in Extracellular space
}
ASSIGNED {
ik (mA/cm2)
diam (micron)
ko (mM)
}
INITIAL {
ki = ki0
}
STATE {
ki (mM)
}
BREAKPOINT {
SOLVE state METHOD cnexp
}
DERIVATIVE state {
ki' = -(1e4)*4*ik/(diam*FARADAY)
ko=ko0
}
```

Simulation using this mechanism shows that with 160 mM K+ on both sides the intracellular [K+] was only reduced by less than 5 mM (160 -> 155.5 mM) by above K+ current in a single compartment cell with L and diam of 1.386 um.

Please help.

P.S. Here is the screenshot of the simulation.