OBJECT				NAPORES			3/14/92 (AS)

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


           	  3am->                 2am->                 am->
  	[m0h1]---------------[m1h1]---------------[m2h1]---------------[m3h1]
          |       <-bm         |       <-2bm        |        <-3bm       |
          |                    |                    |                    |
       /\ |                 /\ |                 /\ |                 /\ |
       ah | bh              ah | bh              ah | bh              ah | bh
          | \/                 | \/                 | \/                 | \/
          |                    |                    |                    |
          |       3am->        |        2am->       |         am->       |
	[m0h0]---------------[m1h0]---------------[m2h0]---------------[m3h0]
           	  <-bm                 <-2bm                 <-3bm


    where [m3h1] = Open State and am, bm, ah and bh have voltage
    dependencies given by:

    am = (malpha_A + malpha_B*Vk)/(malpha_C + exp((malpha_D+Vk)/malpha_F))

    bm = (mbeta_A + mbeta_B*Vk)/(mbeta_C + exp((mbeta_D+Vk)/mbeta_F))

    ah = (halpha_A + halpha_B*Vk)/(halpha_C + exp((halpha_D+Vk)/halpha_F))

    bh = (hbeta_A + hbeta_B*Vk)/(hbeta_C + exp((hbeta_D+Vk)/hbeta_F))

    The total population of pores is given by Nt.  The total number of pores
    within each of the eight stable states at any given iteration is given by
    m0h0, m1h0, m2h0, m3h0, m0h1, m1h1, m2h1, and m3h1, respectively.  The
    total number of pores in the open stable state is given by No = m3h1.
    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   		NaPorePop()
    DATA STRUCTURE   	Na_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:
    Kpores

ERROR MESSAGES:

BUGS:

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