TITLE CaGk : Calcium activated K channel. : Modified from Moczydlowski and Latorre (1983) J. Gen. Physiol. 82 UNITS { (molar) = (1/liter) } UNITS { (mV) = (millivolt) (mA) = (milliamp) (mM) = (millimolar) } NEURON { SUFFIX cagk USEION ca READ cai USEION k READ ek WRITE ik RANGE gbar,gkca,ik GLOBAL oinf, tau } UNITS { FARADAY = (faraday) (kilocoulombs) R = 8.313424 (joule/degC) } PARAMETER { celsius (degC) v (mV) gbar=.01 (mho/cm2) : Maximum Permeability cai (mM) ek (mV) d1 = .84 d2 = 1. k1 = .48e-3 (mM) k2 = .13e-6 (mM) abar = .28 (/ms) bbar = .48 (/ms) st=1 (1) } ASSIGNED { ik (mA/cm2) oinf tau (ms) gkca (mho/cm2) } INITIAL { rate(v,cai) o=oinf } STATE { o } : fraction of open channels BREAKPOINT { SOLVE state METHOD cnexp gkca = gbar*o^st ik = gkca*(v - ek) } DERIVATIVE state { : exact when v held constant; integrates over dt step rate(v, cai) o' = (oinf - o)/tau } FUNCTION alp(v (mV), c (mM)) (1/ms) { :callable from hoc alp = c*abar/(c + exp1(k1,d1,v)) } FUNCTION bet(v (mV), c (mM)) (1/ms) { :callable from hoc bet = bbar/(1 + c/exp1(k2,d2,v)) } FUNCTION exp1(k (mM), d, v (mV)) (mM) { :callable from hoc exp1 = k*exp(-2*d*FARADAY*v/R/(273.15 + celsius)) } PROCEDURE rate(v (mV), c (mM)) { :callable from hoc LOCAL a a = alp(v,c) tau = 1/(a + bet(v, c)) oinf = a*tau }