TITLE klt.mod The low threshold conductance of cochlear nucleus neurons
COMMENT
NEURON implementation of Jason Rothman's measurements of VCN conductances.
This file implements the transient potassium current found in ventral cochlear
nucleus "Type I" cells, which are largely "stellate" or "multipolar" cells (Manis and
Marx, 1991; Rothman and Manis, 2003a,b; Manis et al, 1996). The current is likely
mediated by Kv4.2 potassium channel subunits, but this has not been directly
demonstrated. The specific implementation is described in Rothman and Manis, J.
Neurophysiol. 2003, in the appendix. Measurements were made from isolated
neurons from adult guinea pig, under reasonably stringent voltage clamp conditions.
The measured current is sensitive to 4-aminopyridine.
Original implementation by Paul B. Manis, April (JHU) and Sept, (UNC)1999.
File split implementaiton, April 1, 2004.
Contact: pmanis@med.unc.edu
ENDCOMMENT
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(nA) = (nanoamp)
}
NEURON {
SUFFIX ka
USEION k READ ek WRITE ik
RANGE gkabar, gka, ik
GLOBAL ainf, binf, cinf, atau, btau, ctau
}
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
PARAMETER {
v (mV)
celsius = 22 (degC) : model is defined on measurements made at room temp in Baltimore
dt (ms)
ek = -77 (mV)
gkabar = 0.00477 (mho/cm2) <0,1e9>
}
STATE {
a b c
}
ASSIGNED {
ik (mA/cm2)
gka (mho/cm2)
ainf binf cinf
atau (ms) btau (ms) ctau (ms)
}
LOCAL aexp, bexp, cexp
BREAKPOINT {
SOLVE states
gka = gkabar*(a^4)*b*c
ik = gka*(v - ek)
}
UNITSOFF
INITIAL {
trates(v)
a = ainf
b = binf
c = cinf
}
PROCEDURE states() { :Computes state variables m, h, and n
trates(v) : at the current v and dt.
a = a + aexp*(ainf-a)
b = b + bexp*(binf-b)
c = c + cexp*(cinf-c)
VERBATIM
return 0;
ENDVERBATIM
}
LOCAL q10
PROCEDURE rates(v) { :Computes rate and other constants at current v.
:Call once from HOC to initialize inf at resting v.
q10 = 3^((celsius - 22)/10) : if you don't like room temp, it can be changed!
ainf = (1 / (1 + exp(-1*(v + 31) / 6)))^0.25
binf = 1 / (1 + exp((v + 66) / 7))^0.5
cinf = 1 / (1 + exp((v + 66) / 7))^0.5
atau = (100 / (7*exp((v+60) / 14) + 29*exp(-(v+60) / 24))) + 0.1
btau = (1000 / (14*exp((v+60) / 27) + 29*exp(-(v+60) / 24))) + 1
ctau = (90 / (1 + exp((-66-v) / 17))) + 10
}
PROCEDURE trates(v) { :Computes rate and other constants at current v.
:Call once from HOC to initialize inf at resting v.
LOCAL tinc
TABLE ainf, aexp, binf, bexp, cinf, cexp
DEPEND dt, celsius FROM -150 TO 150 WITH 300
rates(v) : not consistently executed from here if usetable_hh == 1
: so don't expect the tau values to be tracking along with
: the inf values in hoc
tinc = -dt * q10
aexp = 1 - exp(tinc/atau)
bexp = 1 - exp(tinc/btau)
cexp = 1 - exp(tinc/ctau)
}
FUNCTION vtrap(x,y) { :Traps for 0 in denominator of rate eqns.
if (fabs(x/y) < 1e-6) {
vtrap = y*(1 - x/y/2)
}else{
vtrap = x/(exp(x/y) - 1)
}
}
UNITSON