Cav2p1_RI2021_SC

Cav2p1_RI2021_SC#

class braincell.channel.Cav2p1_RI2021_SC(size, g_max=Quantity(0.00022, 'cm / s'), V_sh=Quantity(0., 'mV'), temp=Quantity(296.15, 'K'), name=None)#

Stellate cell Cav2.1 P-type calcium current with GHK drive.

The Cav2.1 (P-type) calcium current of the cerebellar stellate cell model of (Rizza et al., 2021) [3]. Its kinetics were built from dissociated Purkinje neuron recordings reported by (Swensen & Bean, 2005) [1] and published as part of the Purkinje-cell calcium-buffering model of (Anwar, Hong & De Schutter, 2012) [2]. Gating is \(m^3\) with a single activation state, driven by a constant-field (GHK) calcium flux rather than an ohmic term:

\[\begin{split}\begin{aligned} I_{Ca} &= -P \, m^3 \, \Phi(V', [Ca]_i, [Ca]_o, z{=}2, T) \\ m_\infty &= \frac{1}{1 + \exp(-(V' - v_{1/2}) / k)} \\ \tau_m &= \frac{1}{\phi_m} \begin{cases} 0.2702 + 1.1622\, e^{-(V' + 26.798)^2 / 164.19} & V' \geq -40 \\ 0.6923\, e^{V' / 1089.372} & V' < -40 \end{cases} \\ \phi_m &= 3^{(T - 23\,^\circ\mathrm{C}) / 10} \end{aligned}\end{split}\]

where \(V' = V - V_{sh}\), \(v_{1/2} = -29.458\) mV, \(k = 8.429\) mV, \(P\) is the calcium permeability and \(\Phi\) is ghk_flux(). The \(\tau_m\) branch reads \(V'\) in millivolts and returns milliseconds; its branch point is inclusive at exactly \(-40\) mV. \(\phi_m\) is supplied by the Gate declaration, which divides \(\tau_m\) by it.

Parameters:

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

  • g_max (Array | ndarray | bool | number | bool | int | float | complex | Quantity | Callable) – Calcium permeability \(P\) entering the GHK flux – the mod file’s pcabar – despite the g_max name and conductance-like spelling. Defaults to 2.2e-4 cm/s (see Notes).

  • V_sh (Array | ndarray | bool | number | bool | int | float | complex | Quantity | Callable) – Voltage shift subtracted from \(V\) before every rate and before the GHK term; the mod file’s vshift. Defaults to 0.0 mV.

  • temp (Array | ndarray | bool | number | bool | int | float | complex | Quantity) – Absolute temperature. Enters both \(\phi_m\) and the GHK flux. Defaults to 23 degrees Celsius, at which \(\phi_m = 1\).

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

See also

Cav2p1_MA2024_PC

The same mechanism re-imported for the human Purkinje cell model; identical kinetics, different model citation.

Cav2p1_MA2025_BC

The same mechanism re-imported for the basket cell model; identical kinetics, different model citation.

Cav2p1_RI2021_SC_Frozen

Stellate-cell variant with the GHK term’s voltage dependence removed from the autodiff graph. It is not a subclass of this class, and it is not numerically identical to it (see its Notes).

braincell.channel._base.ghk_flux

Shared GHK flux helper called

by

meth:current; the constant-field derivation lives there and is not restated here.

Notes

Ported from SC/channel/Cav2p1_RI21_SC.mod, whose COMMENT records that the mechanism was “Constructed from the recording data provided by Bruce Bean” and cites (Swensen & Bean, 2005) for those recordings. The same file also records the rename “Suffix from newCaP to Cav2_1”.

Two corrections to the mod header’s own model-reference line, “Anwar H, Hong S, De Schutter E (2010) … in Purkinje cell”: the citable record is 2012 – 2010 is the online-first date, which is also why the DOI carries -010- – and the published title ends “Purkinje cells”, plural. Entry [2] below is the corrected form. The header’s “Written by Sungho Hong” line names the mechanism’s author and is deliberately not turned into a citation.

current() evaluates -g_max * m^3 * drive with drive from ghk_flux(), so g_max occupies that function’s permeability slot \(P_s\) and is a permeability in cm/s, not a conductance density. The negation matches BrainCell’s repo-wide inward-positive convention against NEURON’s outward-positive ica.

The shared helper’s physical constants are not the mod file’s. ghk_flux() uses the CODATA Faraday and gas constants and the temperature exactly as passed, whereas this mod file declares F = 9.6485e4, R = 8.3145 and a kelvinfkt conversion of 273.19 + celsius. The resulting flux differs by of order \(10^{-4}\) in relative terms. The frozen variants of this mechanism route through a helper that does carry the mod file’s constants; see Cav2p1_MA2024_PC_Frozen.

The mod file’s vhalfh = -11.039 (mV) and cvh = 16.098 (mV) are declared but never used – the mechanism has no inactivation state – and BrainCell drops them.

The mod file computes taum = taumfkt(v - vshift) / qt with qt = q10^((celsius - 23)/10) and q10 = 3. That is exactly the generic gate temperature path, in which Gate(q10=..., temp_ref=...) divides the whole tau by the factor, so the Q10 is declared on the gate here rather than written into f_m_tau().

The RI2021 import-deviations tables list no TABLE removal, no derivimplicit -> cnexp substitution and no rate-refresh relocation for this mechanism.

g_max’s default is the pcabar of the cell-model deposit this mechanism was imported from – a value tuned for that model, not a permeability reported by either origin paper.

References

current(V, Ca)[source]#

Calculate the current for this ion channel.

This method should be implemented by subclasses to compute the current based on the channel’s specific properties and state.

Parameters:

  • *args – Variable length argument list.

  • **kwargs – Arbitrary keyword arguments.

Raises:

NotImplementedError – This method must be implemented by subclasses.

root_type#

alias of Calcium