TITLE calcium T channel for STh COMMENT Low threshold calcium channel (T-type), Wang et al. 1991 & Coulter et al 1989. The original data was recorded at 22-24degC. How the q10 works: There is a q10 for the rates (alpha and beta's) called Q10 and a Q10 for the maximum conductance called gmaxQ10. The q10s should have been measured at specific temperatures temp1 and temp2 (that are 10degC apart). Ideally, as Q10 is temperature dependant, we should know these two temperatures. We used to follow the more formal Arrhenius derived Q10 approach. The temperature at which this channel's kinetics were recorded is tempb (base temperature). What we then need to calculate is the desired rate scale for now working at temperature celsius (rate_k). This was given by the empirical Arrhenius equation, using the Q10, but now is using the quick Q10 approximation. ENDCOMMENT UNITS { (mV) = (millivolt) (mA) = (milliamp) FARADAY = (faraday) (coulomb) R = (k-mole) (joule/degC) } INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)} NEURON { SUFFIX CaT USEION ca READ cai,cao,eca WRITE ica RANGE gcaT, iCaT GLOBAL activate_Q10,Q10,gmaxQ10,rate_k,gmax_k,temp1,temp2,tempb } PARAMETER { v (mV) dt (ms) gcaT = 0.001 (mho/cm2) iCaT = 0.0 (mA/cm2) eca cai cao celsius activate_Q10 = 1 Q10 = 1.515804730e+00 gmaxQ10 = 1.515804730e+00 temp1 = 19.0 (degC) temp2 = 29.0 (degC) tempb = 23.0 (degC) } STATE { r s d } ASSIGNED { ica (mA/cm2) ralpha (/ms) rbeta (/ms) salpha (/ms) sbeta (/ms) dalpha (/ms) dbeta (/ms) rate_k gmax_k } BREAKPOINT { SOLVE states METHOD cnexp ica = (gcaT*gmax_k)*r*r*r*s*ghkg(v,cai,cao,2) iCaT = ica } UNITSOFF INITIAL { LOCAL ktemp,ktempb,ktemp1,ktemp2 if (activate_Q10>0) { rate_k = Q10^((celsius-tempb)/10) gmax_k = gmaxQ10^((celsius-tempb)/10) }else{ rate_k = 1.0 gmax_k = 1.0 } settables(v) r = ralpha/(ralpha+rbeta) s = (salpha*(dbeta+dalpha) - (salpha*dbeta))/((salpha+sbeta)*(dalpha+dbeta) - (salpha*dbeta)) d = (dbeta*(salpha+sbeta) - (salpha*dbeta))/((salpha+sbeta)*(dalpha+dbeta) - (salpha*dbeta)) } DERIVATIVE states { settables(v) :Computes state variables at the current v and dt. r' = ((ralpha*(1-r)) - (rbeta*r)) d' = ((dbeta*(1-s-d)) - (dalpha*d)) s' = ((salpha*(1-s-d)) - (sbeta*s)) } PROCEDURE settables(v) { :Computes rate and other constants at current v. :Call once from HOC to initialize inf at resting v. :Voltage shift (for temp effects) of -1.9278 added LOCAL bd TABLE ralpha, rbeta, salpha, sbeta, dalpha, dbeta DEPEND celsius FROM -100 TO 100 WITH 400 :"r" CaT activation system ralpha = rate_k * 1.0/(1.7+exp(-(v + 26.2722)/13.5)) rbeta = rate_k * exp(-(v + 61.0722)/7.8)/(exp(-(v + 26.8722)/13.1)+1.7) :"s" CaT fast inactivation system salpha = rate_k * exp(-(v + 158.3722)/17.8) sbeta = rate_k * (sqrt(0.25+exp((v + 81.5722)/6.3))-0.5) * (exp(-(v + 158.3722)/17.8)) :"d" CaT slow inactivation system bd = sqrt(0.25+exp((v + 81.5722)/6.3)) dalpha = rate_k * (1.0+exp((v + 35.4722)/30.0))/(240.0*(0.5+bd)) dbeta = rate_k * (bd-0.5)*dalpha } UNITSON INCLUDE "ghk.inc"