
142 Computational Pharmacokinetics
words, Nature has increased the sensitivity of the system by coupling the re-
ceptor and the transducer. Note that Nature can play with the sensitivity by
increasing (which is called up-regulating the receptor) or decreasing (called
down-regulating the receptor) the total amount R
0
of receptors within the cell
membrane. Receptors are proteins synthesized by the cell and the amount of
them in the cell membrane is the effect of a production/break-down equilib-
rium.
However, as exemplified by the description in Box 6.1, the intracellular
events are typically much more complicated than this model describes and
there is often ...