OBJECT				KPORES			3/14/92 (AS)

DESCRIPTION:
    Simulates a population of potassium ion channel proteins (pores)
    embedded in a patch of membrane over an isopotential region.  Each
    individual pore undergoes standard Markov kinetics through a five state
    scheme:

	      4an->        3an->        2an->         an->
	[n0]---------[n1]---------[n2]---------[n3]---------[n4]
	      <-bn         <-2bn        <-3bn        <-4bn

	where [n4] = Open State and an and bn have voltage dependencies 
	given by:

	an = (alpha_A + alpha_B*Vk)/(alpha_C + exp((alpha_D+Vk)/alpha_F))

	bn = (beta_A + beta_B*Vk)/(beta_C + exp((beta_D+Vk)/beta_F))

	The total population of pores is given by Nt.
	The total number of pores within each of the five stable states
	at any given iteration is given by n0, n1, n2, n3, n4, respectively.
	The total number of pores in the open stable state is given
	by No = n4.
	The open state conductance of a pore is given by Gmax.
	The effective conductance for the population of pores at any
	given iteration is then Gk = Gmax*No.

SPECIFICATIONS:
    FUNCTION   		KPorePop()
    DATA STRUCTURE   	K_pore_type
    CLASS  		segment membrane
    SIZE   		?? bytes
    AUTHOR  		A. Strassberg Caltech 3/92

ACTIONS:
    CHECK 	null
    RESET	sets initial distribution of pores into the various stable
		states based upon the equilibrium solutions to the Markov
		matrix for given Vk.
    PROCESS 	updates the distribution of the stable states of the
		population based upon the rate constants an and bn, derived
		from the current transmembrane voltage Vk.
    INIT 	null

MESSAGES:
    VOLTAGE    	sends transmembrane voltage Vk to the population of pores.
		This Vk is used to update the state distribution after each
		iteration.

FIELDS:
    See DESCRIPTION


RELATED COMMANDS/TOPICS:
    Napores

ERROR MESSAGES:

BUGS:

NOTES:
    See Strassberg and DeFelice, 1993, Neural Computation 5:6
    and the demonstration scripts in Scripts/examples/pore
