TITLE calcium accumulation for STh COMMENT Calcium accumulation into a volume of area*depth next to the membrane with an exponential decay (time constant tau) to resting level (given by the global calcium variable cai0_ca_ion). How the q10 works: There is a q10 for the rates (alpha and beta's) called Q10. 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 are going 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 is given by the empirical Arrhenius equation, using the Q10. ENDCOMMENT NEURON { SUFFIX Cacum USEION ca READ ica WRITE cai GLOBAL con,cai0,buftau,activate_Q10,Q10,rate_k,temp1,temp2,tempb,depth } UNITS { (mM) = (milli/liter) (mA) = (milliamp) F = (faraday) (coulombs) : Faradays constant } PARAMETER { v (mV) dt (ms) con = 0.0 : conversion constant (see INITIAL block) Avo = 6.02e23 : Avogadro's number elc = 1.602e-19 (coulombs) : elementrary charge depth = 200.0 (nm) : assume volume = area*depth cai0 = 0.0001(mM) : replace cai0_ca_ion buftau = 1.857456645e+02 (ms) cai0_ca_ion celsius activate_Q10 = 1 Q10 = 1.2 temp1 = 19.0 (degC) temp2 = 29.0 (degC) tempb = 23.0 (degC) } ASSIGNED { ica (mA/cm2) tau (ms) rate_k } STATE { cai (mM) } BREAKPOINT { SOLVE integrate METHOD cnexp } UNITSOFF INITIAL { LOCAL ktemp,ktempb,ktemp1,ktemp2 if (activate_Q10>0) { ktemp = celsius+273.0 ktempb = tempb+273.0 ktemp1 = temp1+273.0 ktemp2 = temp2+273.0 rate_k = exp( log(Q10)*((1/ktempb)-(1/ktemp))/((1/ktemp1)-(1/ktemp2)) ) }else{ rate_k = 1.0 } con=1e7/(depth*2.0*Avo*elc) : UNITS (derivation) : ica = (mA/cm2) : = (A/1e3cm2) : = ((C/s)/1e3cm2) : depth = (nm) = (1e-7cm) : ica/depth = ((C/s)/1e3cm2) * 1/(1e-7cm) : = ((C/s)/1e3cm2) * 1e7/(cm) : = (1e7(C/s) * 1/(1e3cm3)) : = (1e7(C/s) * 1/(litres)) : 1e7*ica/depth = ((C/s) * 1/(litres)) : = ((C/litres) * 1/(s)) : = ((C/litres) * 1/(1e3msec)) : = ((C/litres) * 1e-3/(msec)) : 1e4*ica/depth = ((C/litres) * 1/(msec)) : 1/(2*Avo*elc) = (mol/C) : = (1e3mmol/C) : 1e3/(2*Avo*elc) = (mmol/C) : 1e4*ica/depth * 1e3/(2*Avo*elc) = ((C/litres) * 1/(msec)) : * (mmol/C) : ica*1e7/(depth*2*Avo*elc) = (mmol/litres) * (1/msec) : ica*con = (mM) * (1/msec) tau=buftau/rate_k cai=cai0 } DERIVATIVE integrate { cai' = -ica*con + (cai0 - cai)/tau } UNITSON