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NaT.m
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NaT.m
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function [gna] = NaT(Vm,dt,NumChan,stochastic)
t=dt:dt:(length(Vm).*dt);
% NA ARRAYS
m = zeros(1,length(t));
h = zeros(1,length(t));
m1h1 = zeros(1,length(t));
m2h1 = zeros(1,length(t));
m3h1 = zeros(1,length(t));
m4h1 = zeros(1,length(t));
m1h2 = zeros(1,length(t));
m2h2 = zeros(1,length(t));
m3h2 = zeros(1,length(t));
m4h2 = zeros(1,length(t));
gnasingle = 0.000025; % ~20 pS is the estimated single channel conductance of NaT, NaP and DrK
gnabar = gnasingle.*NumChan;
N_NA = NumChan;
i=1;
Vrest = Vm(1,i);
% Possible MATLAB equivalent expressions:
alpm(1,1) = 3.42.*( 0.11111.*(Vrest+33))./(1-exp(-0.11111.*(Vrest+33)));
betm(1,1) = 27.6.*(-0.083333.*(Vrest+58))./(1-exp(0.083333.*(Vrest+58)));
beth(1,1) = 0.45.*( 0.11111.*(Vrest+21))./(1-exp(-0.11111.*(Vrest+21)));
alph(1,1) = 0.36.*(-0.083333.*(Vrest+48))./(1-exp(0.083333.*(Vrest+48)));
m(1,i) = alpm(1,1) ./ (alpm(1,1) + betm(1,1));
h(1,i) = alph(1,1) ./ (alph(1,1) + beth(1,1));
if stochastic==1
m2 = round( [3.*alpm(1,1) ./ (3.*alpm(1,1) + betm(1,1))] .* N_NA );
m3 = round( [2.*alpm(1,1) ./ (2.*alpm(1,1) + 2.*betm(1,1))] .* N_NA );
m4 = round( [1.*alpm(1,1) ./ (1.*alpm(1,1) + 3.*betm(1,1))] .* N_NA );
m1 = N_NA - [m2 + m3 + m4];
m2h1(1,i) = round( m2 - m2 .* [alph(1,1) ./ (alph(1,1) + beth(1,1))] );
m3h1(1,i) = round( m3 - m3 .* [alph(1,1) ./ (alph(1,1) + beth(1,1))] );
m4h1(1,i) = round( m4 - m4 .* [alph(1,1) ./ (alph(1,1) + beth(1,1))] );
m1h1(1,i) = round( m1 - m1 .* [alph(1,1) ./ (alph(1,1) + beth(1,1))] );
m2h2(1,i) = m2 - m2h1(1,i);
m3h2(1,i) = m3 - m3h1(1,i);
m4h2(1,i) = m4 - m4h1(1,i);
m1h2(1,i) = m1 - m1h1(1,i);
N_Occup_Na = [m1h1(1,i),m2h1(1,i),m3h1(1,i),m4h1(1,i);m1h2(1,i),m2h2(1,i),m3h2(1,i),m4h2(1,i)];
end
for i = 2:length(Vm)
% Possible MATLAB equivalent expressions:
alpm(1,1) = 3.42.*(0.11111.*(Vm(1,i-1)+33))./(1-exp(-0.11111.*(Vm(1,i-1)+33)));
betm(1,1) = 27.6.*(-0.083333.*(Vm(1,i-1)+58))./(1-exp(0.083333.*(Vm(1,i-1)+58)));
beth(1,1) = 0.45.*(0.11111.*(Vm(1,i-1)+21))./(1-exp(-0.11111.*(Vm(1,i-1)+21)));
alph(1,1) = 0.36.*(-0.083333.*(Vm(1,i-1)+48))./(1-exp(0.083333.*(Vm(1,i-1)+48)));
if stochastic == 1
N_Occup_Na = [m1h1(i-1),m2h1(i-1),m3h1(i-1),m4h1(i-1);m1h2(i-1),m2h2(i-1),m3h2(i-1),m4h2(i-1)];
P_Trans_m = [dt.*alpm(1,1).*[3,2,1];dt.*betm(1,1).*[1,2,3]];
P_Trans_h = [dt.*alph(1,1);dt.*beth(1,1)];
if max(N_Occup_Na(1,:))>N_NA || max(N_Occup_Na(2,:))>N_NA || min(N_Occup_Na(1,:))<0 || min(N_Occup_Na(2,:))<0
disp('ERROR: Na Channel occupancies outside acceptable range');
disp(N_Occup_Na);
disp(i);
return
end
for j=1:4
if N_Occup_Na(1,j) > 0
tmp1 = rand(1,N_Occup_Na(1,j));
else % Make sure no transitions can occur out of this state if it is unpopulated
tmp1 = 1e67;
end
if N_Occup_Na(2,j) > 0
tmp2 = rand(1,N_Occup_Na(2,j));
else % Make sure no transitions can occur out of this state if it is unpopulated
tmp2 = 1e67;
end
switch j
case 1,
tmp_1h = (tmp1 <= P_Trans_h(2,1));
T_Change_h(1,j) = sum(tmp_1h,2);
tmp3 = (tmp1 <= [P_Trans_m(1,j)+P_Trans_h(2,1)] & tmp1 > P_Trans_h(2,1));
T_Change_a(1,j) = sum(tmp3,2);
tmp_2h = (tmp2 < P_Trans_h(1,1));
T_Change_h(2,j) = sum(tmp_2h,2);
tmp4 = (tmp2 < [P_Trans_m(1,j)+P_Trans_h(1,1)] & tmp2 > P_Trans_h(1,1));
T_Change_a(2,j) = sum(tmp4,2);
case {2,3},
tmp_1h = (tmp1 <= P_Trans_h(2,1));
T_Change_h(1,j) = sum(tmp_1h,2);
tmp3 = (tmp1 <= [P_Trans_m(1,j)+P_Trans_h(2,1)] & tmp1 > P_Trans_h(2,1));
T_Change_a(1,j) = sum(tmp3,2);
tmp5 = (tmp1 <= [P_Trans_m(2,j-1)+P_Trans_h(2,1)+P_Trans_m(1,j)] & tmp1 > [P_Trans_m(1,j)+P_Trans_h(2,1)]);
T_Change_b(1,j) = sum(tmp5,2);
tmp_2h = (tmp2 <= P_Trans_h(1,1));
T_Change_h(2,j) = sum(tmp_2h,2);
tmp4 = (tmp2 <= [P_Trans_m(1,j)+P_Trans_h(1,1)] & tmp2 > P_Trans_h(1,1));
T_Change_a(2,j) = sum(tmp4,2);
tmp6 = (tmp2 <= [P_Trans_m(2,j-1)+P_Trans_h(1,1)+P_Trans_m(1,j)] & tmp2 > [P_Trans_m(1,j)+P_Trans_h(1,1)]);
T_Change_b(2,j) = sum(tmp6,2);
case 4,
tmp_1h = (tmp1 <= P_Trans_h(2,1));
T_Change_h(1,j) = sum(tmp_1h,2);
tmp5 = (tmp1 <= [P_Trans_m(2,j-1)+P_Trans_h(2,1)] & tmp1 > P_Trans_h(2,1));
T_Change_b(1,j) = sum(tmp5,2);
tmp_2h = (tmp2 <= P_Trans_h(1,1));
T_Change_h(2,j) = sum(tmp_2h,2);
tmp6 = (tmp2 <= [P_Trans_m(2,j-1)+P_Trans_h(1,1)] & tmp2 > P_Trans_h(1,1));
T_Change_b(2,j) = sum(tmp6,2);
end
end
% Update states with number of transitions in - out
m1h1(1,i)= m1h1(1,i-1) + T_Change_h(2,1) + T_Change_b(1,2) - T_Change_h(1,1) - T_Change_a(1,1);
m1h2(1,i)= m1h2(1,i-1) + T_Change_h(1,1) + T_Change_b(2,2) - T_Change_h(2,1) - T_Change_a(2,1);
m2h1(1,i)= m2h1(1,i-1) + T_Change_a(1,1) + T_Change_b(1,3) + T_Change_h(2,2) - T_Change_b(1,2) - T_Change_a(1,2) - T_Change_h(1,2);
m2h2(1,i)= m2h2(1,i-1) + T_Change_a(2,1) + T_Change_b(2,3) + T_Change_h(1,2) - T_Change_b(2,2) - T_Change_a(2,2) - T_Change_h(2,2);
m3h1(1,i)= m3h1(1,i-1) + T_Change_a(1,2) + T_Change_b(1,4) + T_Change_h(2,3) - T_Change_b(1,3) - T_Change_a(1,3) - T_Change_h(1,3);
m3h2(1,i)= m3h2(1,i-1) + T_Change_a(2,2) + T_Change_b(2,4) + T_Change_h(1,3) - T_Change_b(2,3) - T_Change_a(2,3) - T_Change_h(2,3);
m4h1(1,i)= m4h1(1,i-1) + T_Change_h(2,4) + T_Change_a(1,3) - T_Change_h(1,4) - T_Change_b(1,4);
m4h2(1,i)= m4h2(1,i-1) + T_Change_h(1,4) + T_Change_a(2,3) - T_Change_h(2,4) - T_Change_b(2,4);
gna(1,i) = gnasingle .* m4h1(1,i);
else
m(1,i) = m(1,i-1) + ( ( (alpm(1,1) .* (1 - m(1,i-1))) - (betm(1,1) .* m(1,i-1)) ) .* dt );
h(1,i) = h(1,i-1) + ( ( (alph(1,1) .* (1 - h(1,i-1))) - (beth(1,1) .* h(1,i-1)) ) .* dt );
gna(1,i) = gnabar .* m(1,i-1).^3 .* h(1,i-1);
end
end
plot(t, gna);