Figure 1.
The cell membrane acts as a capacitance, which is submitted to the membrane potential . Three blocks exchange ions between the cytosol and the outer medium: they induce electroneutral transports (with the
and
exchangers), electrogenic currents via the Na/K-ATPase, and passive ion channels (for
,
, and
). The chemical reactions are assumed to take place within an homogenous cytosol.
Figure 2.
Three dimensional representation of steady-state pH.
pH is drawn as a function of the two controlling parameters and
. The flattest area of this surface stretches over
units around physiological pH (7.2, in black). This corresponds to values that can be reached by cellular systems (red boundaries).
Figure 3.
pH modification by changes in biochemical constants.
The reference values are ,
,
,
and
. For
and
modification, the ratio
is held constant (see text for the explanation).
Figure 4.
Forced acidosis by a simulated spike.
The rise and the decrease of are highlighted by blue areas. (A) The expected pH overshoot takes place with or without the presence of a 60 mM physiological buffer (dashed lines). (B) The ionic ratios relative to the initial values are reported as well.
Figure 5.
Lactate production occurs with a constant , a
buffer, and with transporters working at their nominal level. The lactate accumulation is highlighted by a green area. (A) The predicted pH overshoot takes place during the lactate removal by the monocarboxylate transporters. (B) The corresponding ionic ratios relative to the initial values.