# The Keizer-Smolen model,
# PNAS, Vol. 88, pp. 3897-3901, 1991.

#
# Initial values of the variables.
#
init v=-64, pc=1, po=0, j=0.86, n=0, cai=0.1

#
# Values of the model parameters.
#
params cm=5310, kca=0.24, f=0.015, xf=0.45, gamma=0.0000045
###### for the goldman-hodgkin-katz equation:
params gca=1470, rt2f=13.35, cao=8
###### for icaf:
params vmf=-8, smf=10, kminus=0.002, kstar=-0.000047, taumbar=1.2820513
###### for icas:
params vms=2, sms=14, vj=-40, sj=7, taujbar=30000
###### for ik:
params gk=2500, vk=-75, vn=-13, sn=5.6, taunbar=20, vbar=-75, sa=65, sb=20
###### for ikatp:
params gkatp=380

#
# Activation and inactivation functions.
#
minff(v) = 1/(1+exp((vmf-v)/smf))
alpha(v) = minff(v)/taumbar
beta(v)  = (1-minff(v))/taumbar
minfs(v) = 1/(1+exp((vms-v)/sms))
jinf(v)  = 1/(1+exp((v-vj)/sj))
tauj(v)  = taujbar/(exp((v-vj)/(2*sj))+exp((vj-v)/(2*sj)))
ninf(v)  = 1/(1+exp((vn-v)/sn))
taun(v)  = taunbar/(exp((v-vbar)/sa)+exp((vbar-v)/sb))

#
# Currents.
#
ghk(v) = cao*v/(1-exp(v/rt2f))
icaf(v,po) = gca*po*xf * ghk(v)
icas(v,j) = gca*minfs(v)*j*(1-xf) * ghk(v)
icatot(v,po,j) = icaf(v,po) +  icas(v,j)
ik(v,n)   = gk*n*(v-vk)
ikatp(v ) = gkatp*(v-vk)

#
# Differential equations.
#
v'   = -(icatot(v,po,j)+ik(v,n)+ikatp(v))/cm
pc'  = -alpha(v)*pc + beta(v)*po
po'  = kminus*(1-po-pc) - kstar*ghk(v)*po + alpha(v)*pc - beta(v)*po
j'   = (jinf(v)-j)/tauj(v)
n'   = (ninf(v)-n)/taun(v)
cai' = f*( -icatot(v,po,j)*gamma - kca*cai )

#
# Specify some internal XPP parameters.
#
@ maxstor=12000
@ total=20000, dt=2, bounds=10000
@ method=gear, toler=0.000001, dtmin=0.0001, dtmax=10
@ xlo=0, xhi=20000, ylo=-70, yhi=0

done