: Ca-dependent K channels (BK) - alphabeta4 and alpha : Bin Wang, Robert Brenner, and David Jaffe - Originally written May 27, 2010 : : June 1, 2010 - added double exponential function for voltage-dependent activation : : July 3, 2010 - changed voltage-dependence for the two channels based on revised data : : April 2, 2011 - adjusted parameters based on updated Bin data : modified by Yunliang October 19th, 2015 : Notice that the experiments are done under room temperature after checking with David Jaffe!!!! : However, to make slow component function during the ISI, here the Q10 correction is not included. NEURON { SUFFIX abBK USEION ca READ cai USEION k READ ek WRITE ik RANGE gabkbar,gabk, ik : THREADSAFE } UNITS { (molar) = (1/liter) (mM) = (millimolar) (mV) = (millivolt) (mA) = (milliamp) (S) = (siemens) } CONSTANT { q10 = 3 } PARAMETER { gabkbar = .01 (S/cm2) : maximum permeability - alphabeta cai (mM) base = 1 (mV) : alphabeta4 base time constant } ASSIGNED { v (mV) ek (mV) ik (mA/cm2) gabk (S/cm2) abinf (mV) abtau (ms) qt } STATE { ab } BREAKPOINT { SOLVE state METHOD cnexp gabk = gabkbar*ab ik = (gabk)*(v - ek) } DERIVATIVE state { : exact when v held constant; integrates over dt step rates(v, cai) ab' = (abinf-ab)/abtau } INITIAL { qt = q10^((celsius-34 (degC))/10 (degC)) rates(v, cai) ab = abinf } : alpha-beta4 channel properties FUNCTION shiftab(cai (mM)) { shiftab = 25 - 55.7 + 136.9*exp(-.28*cai*1e3) } FUNCTION peakab(cai (mM)) { peakab = 13.7 + 234*exp(-.72*cai*1e3) } : Double sigmoid function for tau voltage-dependence FUNCTION taufunc(v (mV)) { taufunc = 1 / ( (10*(exp(-v/63.6) + exp (-(150-v)/63.6))) - 5.2 ) if (taufunc <= 0.2) { : stop the function between 0.2 and 1 taufunc = 0.2 } } PROCEDURE rates(v (mV), cai (mM)) { LOCAL range, vv : alpha-beta4 model abinf = -56.449 + 104.52*exp(-.22964*cai*1e3) + 295.68*exp(-2.1571*cai*1e3) abinf = 1/(1+exp((abinf-v)/(25/1.6))) vv = v + 100 - shiftab(cai) abtau = taufunc(vv) range = peakab(cai)-base abtau = ((range*((abtau-.2)/.8)) + base)/qt*2*2 }