Pharmacology for Anaesthesia and Intensive Care

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3 Drug action

Ligand Receptor

Ions

Enzyme

Intermediate

messenger

3

G

Cell

membrane

Altered ion

permeability

Intermediate

messenger

production

Regulation of gene

transcription. Receptors

are sited within the cell

membrane or the nucleus.

AB

1

2

Figure 3.1.Mechanism of action of the three groups of receptors.

with ionotropic for ion-channel forming receptors. As well as transmitting a stimu-

lus across the cell membrane the G-protein system produces signal amplification,

whereby a modest stimulus may have a much greater intracellular response. This

amplification occurs at two levels: a single activated GPCR can stimulate multiple

G-proteins and each G-protein can activate several intermediate messengers.