CaHT_HM1992

CaHT_HM1992#

class braincell.channel.CaHT_HM1992(size, g_max=Quantity(2., 'mS / cm^2'), temp=Quantity(309.15, 'K'), q10_p=3.55, temp_ref_p=Quantity(297.15, 'K'), q10_q=3.0, temp_ref_q=Quantity(297.15, 'K'), V_sh=Quantity(25., 'mV'), name=None)#

Depolarized-shift variant of the Huguenard & McCormick 1992 T current.

\(p^2 q\) HH gating with an ohmic driving force, using the same rate functions as CaT_HM1992 but with the threshold shift moved from -3.0 mV to +25.0 mV (see Notes for why this is not a citation for a genuine high-threshold current):

\[\begin{split}\begin{aligned} p_\infty &= \frac{1}{1 + \exp(-(V' + 59) / 6.2)} \\ \tau_p &= \frac{1} {\exp(-(V' + 132) / 16.7) + \exp((V' + 16.8) / 18.2)} + 0.612 \\ q_\infty &= \frac{1}{1 + \exp((V' + 83) / 4)} \\ \tau_q &= \begin{cases} \exp((V' + 467) / 66.6) & V' < -80 \\ \exp(-(V' + 22) / 10.5) + 28 & V' \geq -80 \end{cases} \end{aligned}\end{split}\]

where \(V' = (V - V_{sh}) / \mathrm{mV}\) and \(\tau_p\)/\(\tau_q\) (in milliseconds) are further scaled by gate_phi().

Parameters:

  • size (int | Sequence[int] | integer | Sequence[integer]) – Channel state shape.

  • g_max (Array | ndarray | bool | number | bool | int | float | complex | Quantity | Callable) – Maximal conductance density. Defaults to 2.0 mS/cm2.

  • temp (Array | ndarray | bool | number | bool | int | float | complex | Quantity) – Absolute temperature driving the Q10 factors, default 36 degrees Celsius.

  • q10_p (Array | ndarray | bool | number | bool | int | float | complex | Quantity | Callable) – Q10 scaling factor for the activation gate, default 3.55, inherited unchanged from CaT_HM1992 (see that class’s Notes on this value’s provenance).

  • temp_ref_p (Array | ndarray | bool | number | bool | int | float | complex | Quantity) – Reference temperature for q10_p, default 24 degrees Celsius.

  • q10_q (Array | ndarray | bool | number | bool | int | float | complex | Quantity | Callable) – Q10 scaling factor for the inactivation gate, default 3.0.

  • temp_ref_q (Array | ndarray | bool | number | bool | int | float | complex | Quantity) – Reference temperature for q10_q, default 24 degrees Celsius.

  • V_sh (Array | ndarray | bool | number | bool | int | float | complex | Quantity | Callable) – Threshold shift applied to both gates’ rates, default +25.0 mV – see Notes; this is the only numeric difference from CaT_HM1992.

  • name (str | None) – Optional channel name.

See also

CaT_HM1992

The unshifted low-threshold T current this class is character-for-character derived from (V_sh = -3.0 mV); see its Notes for how the source paper’s 2 mV screening shift is folded into these same rate functions.

CaHT_Re1993

Independently sourced high-threshold calcium current with a genuine high-voltage-activated attribution.

Notes

This class does not implement a current described in (Huguenard & McCormick, 1992). That paper [1] models exactly four currents – a low-threshold T-type calcium current, two potassium currents and a hyperpolarization-activated current – and contains no high-threshold or high-voltage-activated calcium current at all. Reading the code confirms this class’s rate functions are character-for-character identical to CaT_HM1992’s (same 59, 6.2, 0.612, 132, 16.7, 16.8, 18.2, 83, 4.0, 467, 66.6, 22, 10.5, 28 constants, the same \(V' = -80\) branch point, the same p^2 q gating and the same q10_p = 3.55 / q10_q = 3.0 at 24 degC defaults). The only difference is V_sh: +25.0 mV here versus -3.0 mV in CaT_HM1992. This class is the paper’s low-threshold T current translated 28 mV depolarized and relabelled “high-threshold” – a BrainCell/BrainPy-derived variant, not a current the cited paper reports. The +25 mV shift itself has no traceable source in the paper.

The citation below is included because it correctly identifies the origin of the gating kinetics (they are exactly Huguenard & McCormick’s T-current rate functions – see CaT_HM1992 for the full derivation and the 2 mV screening-shift caveat that also applies here), not because the paper describes a high-threshold current under this name. A genuine high-threshold thalamic calcium current, \(I_L\), is described in the companion paper McCormick, D. A., & Huguenard, J. R. (1992), “A model of the electrophysiological properties of thalamocortical relay neurons”, Journal of Neurophysiology, 68(4), 1384-1400, doi:10.1152/jn.1992.68.4.1384 – but this class’s gating functions do not match that current’s kinetics either, so that paper is named here only as a lead for future re-derivation, not cited.

References

root_type#

alias of Calcium