qgis - Calling GRASS modules in pyQGIS?

I wish to use a Grass module (v.to.db) in QGis, without the grass toolbox.

I tried with the Python console, but to no avail :

• Using Sextante plugin but obviously it didn't know all the grass modules.

from sextante.core.Sextante import Sextante

Sextante.alghelp("grass:v.to.db")

--> Algorithm not found

• An other test :

grass.run_command("v.to.db", map='bl@PERMANENT', layer='2', option='start', units='meters', columns='X,Y,Z')

-->Traceback (most recent call last):

File "", line 1, in module

NameError: name 'grass' is not defined

Do you know if there is an other way to use the grass module ? I don't want to use it in the grass toolbox because I can select only one colums in "attribute field", and I would like to choose several columns.