difference between <-> and << ?

[xyang]

Hi, How are you?

I read from NEURON book about chemical reaction and understant the equation (page 238):
~ cai + pump <-> capump (k1, k2)

However, I also saw sodium diffusion in Dr. Canavier's paper (1999) as:
~ nai << (-ina/(FARADAY)*PI*diam*(1e4))

Where can I find the explanation for the symbol "<<"
Thank you!
Have a great day!

Xianghong

[ted]

Where can I find the explanation for the symbol "<<"

Symbols are listed in the Index. On page 413, the first page of the Index, you will find

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<< (explicit flux) -- see KINETIC block: << (explicit flux)

KINETIC block terms are referenced on page 435, where you will find

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KINETIC block . . .
 . . .
  << (explicit flux) 253

The paragraph on the bottom of page 253 discusses this statement

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~ ca[0] << (-ica*PI*diam/(2*FARADAY)) : ica is Ca efflux

from a calcium accumulation mechanism. Quoting from that paragraph:

[ this statement ] is equivalent to a differential equation that describes the
contribution of transmembrane calcium current to Ca2+ in the outermost
shell. The << signifies an explicit flux.

In other words, calcium current is a flux of calcium ions that leaves or
enters the cytoplasm that is just inside the cell membrane.

[xyang]

Hi, Ted:
Thank you for the explanation! This is very clear and helpful!
Best regards,

Xianghong