COMMENT
Ih current - hyperpolarization-activated nonspecific Na and K channel
- contributes to the resting membrane potential
- controls the afterhyperpolarization
Reference:
1. Maccaferri, G. and McBain, C.J. The hyperpolarization-activated current
(Ih) and its contribution to pacemaker activity in rat CA1 hippocampal
stratum oriens-alveus interneurons, J. Physiol. 497.1:119-130,
1996.
V1/2 = -84.1 mV
k = 10.2
reversal potential = -32.9 +/- 1.1 mV
at -70 mV, currents were fitted by a single exponetial of t = 2.8+/- 0.76 s
at -120 mV, two exponentials were required, t1 = 186.3+/-33.6 ms
t2 = 1.04+/-0.16 s
2. Maccaferri, G. et al. Properties of the
Hyperpoarization-activated current in rat hippocampal CA1 Pyramidal
cells. J. Neurophysiol. Vol. 69 No. 6:2129-2136, 1993.
V1/2 = -97.9 mV
k = 13.4
reversal potential = -18.3 mV
3. Pape, H.C. Queer current and pacemaker: The
hyperpolarization-activated cation current in neurons, Annu. Rev.
Physiol. 58:299-327, 1996.
single channel conductance is around 1 pS
average channel density is below 0.5 um-2
0.5 pS/um2 = 0.00005 mho/cm2 = 0.05 umho/cm2
4. Magee, J.C. Dendritic Hyperpolarization-Activated Currents Modify
the Integrative Properties of Hippocampal CA1 Pyramidal Neurons, J.
Neurosci., 18(19):7613-7624, 1998
Deals with Ih in CA1 pyramidal cells. Finds that conductance density
increases with distance from the soma.
soma g = 0.0013846 mho/cm2
dendrite g (300-350 um away) = 0.0125 mho/cm2
see Table 1 in th paper
ENDCOMMENT
UNITS {
(mA) = (milliamp)
(mV) = (millivolt)
}
NEURON {
SUFFIX Ihvip
USEION h READ eh WRITE ih VALENCE 1
RANGE gkhbar,ih
GLOBAL rinf, rexp, tau_r
}
INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}
PARAMETER {
v (mV)
p = 5 (degC)
dt (ms)
gkhbar = 0.001385 (mho/cm2)
eh = -32.9 (mV)
}
STATE {
r
}
ASSIGNED {
ih (mA/cm2)
rinf rexp
tau_r
}
BREAKPOINT {
SOLVE deriv METHOD derivimplicit
ih = gkhbar*r*(v - eh)
}
INITIAL {
rates(v)
r = rinf
}
DERIVATIVE deriv { :Computes state variable h at current v and dt.
rates(v)
r' = (rinf - r)/tau_r
}
PROCEDURE rates(v) { :Computes rate and other constants at current v.
:Call once from HOC to initialize inf at resting v.
TABLE rinf, rexp, tau_r DEPEND dt, p FROM -200 TO 100 WITH 300
rinf = 1/(1 + exp((v+84.1)/10.2))
rexp = 1 - exp(-dt/(tau_r))
tau_r = 100 + 1/(exp(-17.9-0.116*v)+exp(-1.84+0.09*v))
}
UNITSON