;;  -*- Hen -*-

;;
;; This model is used to calculate the channel conductance assuming
;; some initial state. The calculation is based on sodium ion flow,
;; potassium ion flow and leakage ion flow. (Hodgkin, A. L. and Huxley,
;; A. F. (1952) "A Quantitative Description of Membrane Current and its
;; Application to Conduction and Excitation in Nerve" Journal of
;; Physiology 117: 500-544)
;;

(nemo-model hodgkin-huxley

      ((input v)

       (const Vrest = -65)

       (component (type membrane-capacitance)
	   (const C = 1)
	   (output C))

       (component (type ionic-current)

         (component (type gate)
		  
	    ;; rate functions
	    (defun amf (v)   (0.1  *  ((v + 40) / (1.0 - (exp ((neg (v + 40)) / 10))))))
	    (defun bmf (v)   (4.0  *  (exp ((neg (v + 65)) / 18))))
	    (defun ahf (v)   (0.07 *  (exp ((neg (v + 65)) / 20))))
	    (defun bhf (v)   (1.0  /  (1.0 + (exp ((neg (v + 35)) / 10)))))

	    ;; model states
	    
	    ;; the value of state complex m is determined by state m1 (open state)
	    ;;
	    ;; each statement in the transitions block is of the form (-> SRC DEST RATE)
	    ;;
	    (reaction (m (transitions (<-> C O (amf (v)) (bmf (v))) )
			      ;(initial (amf (Vrest) / (amf (Vrest) + bmf (Vrest))) ) 
			      (conserve (1 = (C + O)))
			      (open O)  (power 3)))
	    
	    ;; the value of state complex h is determined by state h1 (open state)
	    (reaction (h (transitions (<-> C O (ahf (v)) (bhf (v))))
			      ;(initial (ahf (Vrest) / (ahf (Vrest) + bhf (Vrest))) ) 
			      (conserve (1 = (C + O)))
			      (open O) (power 1)))
	    
	    ;; state definitions exported by this model
	    (output m h )  
	    )

	 (component (type pore)
	    (const gbar_Na  = 120)
	    (output gbar_Na )
	    )

	 (component (type permeating-ion) (name na)
		    (const e_Na = 50)
		    (output e_Na ))

	 
	 )

       (component (type ionic-current)

         (component (type gate)
		    
	    ;; rate functions
	    (defun anf (v)   (0.01  * ((v + 55) / (1 - (exp ((neg (v + 55)) / 10))))))
	    (defun bnf (v)   (0.125 * (exp ((neg (v + 65)) / 80))))

	    ;; model states
	    
	    ;; the value of state complex m is determined by state m1 (open state)
	    ;;
	    ;; each statement in the transitions block is of the form (-> SRC DEST RATE)
	    ;;
	    ;; the value of state complex n is determined by state n1 (open state)
	    (reaction (n (transitions (<-> C O (anf (v)) (bnf (v))) )
			      ;(initial (anf (Vrest) / (anf (Vrest) + bnf (Vrest))) ) 
			      (conserve (1 = (C + O)))
			      (open O)  (power 4)))
	    
	    ;; state definitions exported by this model
	    (output n)
	    )

	 (component (type pore)
	    (const   gbar_K   = 36)
	    (output  gbar_K ))

	 (component (type permeating-ion) (name k)
		    (const e_K = -77)
		    (output e_K ))


	  )


       (component (type ionic-current) (name Leak)
		  
		  (component (type pore)
			     (const  gbar_Leak  = 0.3)
			     (output gbar_Leak ))
		  
		  (component (type permeating-ion) (name non-specific)
			     (const e_Leak = -54.4)
			     (output e_Leak ))
	      
	      ) ;; end leak current

       ))