TITLE kht.mod The high threshold conductance of cochlear nucleus neurons
COMMENT
NEURON implementation of Jason Rothman's measurements of VCN conductances.
This file implements the high threshold potassium current found in several brainstem
nuclei of the auditory system, including the spherical and globular bushy cells
(Manis and Marx, 1991; Rothman and Manis, 2003a,b) and multipolar (stellate)
cells of the ventral cochlear nucleus, principal cells of the medial
nucleus of the trapzoid body (Brew and Forsythe, 1995, Wang and Kaczmarek,
1997) and neurons of the medial superior olive. The current is likely mediated by
Kv3.1 potassium channel subunits. 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 4aminopyridine and TEA, but is spared by mamba snake toxi
dendrotoxin I.
Similar conductrances are found in the homologous neurons of the avian auditory
system (Reyes and Rubel; Zhang and Trussell; Rathouz and Trussell), and the
conductance described here, in the absence of more detailed kinetic measurements
, is probably suitable for use in modeling that system.
Original implementation by Paul B. Manis, April (JHU) and Sept, (UNC)1999.
File split implementation, February 28, 2004.
Contact: pmanis@med.unc.edu
ENDCOMMENT
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
(nA) = (nanoamp)
}
NEURON {
SUFFIX kht
USEION k READ ek WRITE ik
RANGE gkhtbar, gkht, ik
GLOBAL ninf, pinf, ntau, ptau
}
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)
gkhtbar = 0.01592 (mho/cm2) <0,1e9>
nf = 0.85 <0,1> :proportion of n vs p kinetics
}
STATE {
n p
}
ASSIGNED {
ik (mA/cm)
gkht (mho/cm2)
pinf ninf
ptau (ms) ntau (ms)
}
LOCAL nexp, pexp
BREAKPOINT {
SOLVE states
gkht = gkhtbar*(nf*(n^2) + (1nf)*p)
ik = gkht*(v  ek)
}
UNITSOFF
INITIAL {
trates(v)
p = pinf
n = ninf
}
PROCEDURE states() { :Computes state variables m, h, and n
trates(v) : at the current v and dt.
n = n + nexp*(ninfn)
p = p + pexp*(pinfp)
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!
ninf = (1 + exp((v + 15) / 5))^0.5
pinf = 1 / (1 + exp((v + 23) / 6))
ntau = (100 / (11*exp((v+60) / 24) + 21*exp((v+60) / 23))) + 0.7
ptau = (100 / (4*exp((v+60) / 32) + 5*exp((v+60) / 22))) + 5
}
PROCEDURE trates(v) { :Computes rate and other constants at current v.
:Call once from HOC to initialize inf at resting v.
LOCAL tinc
TABLE ninf, nexp, pinf, pexp
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
nexp = 1  exp(tinc/ntau)
pexp = 1  exp(tinc/ptau)
}
FUNCTION vtrap(x,y) { :Traps for 0 in denominator of rate eqns.
if (fabs(x/y) < 1e6) {
vtrap = y*(1  x/y/2)
}else{
vtrap = x/(exp(x/y)  1)
}
}
UNITSON
