TWO FAMILIES

How a receptor answers

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Ionotropic

A receptor that is also an ion channel. Binding opens it directly

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Metabotropic

A receptor that activates a G protein, starting a signaling cascade inside the cell

One is a door, the other is a doorbell.

SIDE BY SIDE

Direct or relayed

Both start with the transmitter binding to the receptor, but what happens next differs.

Speed is the key difference.

IONOTROPIC

Fast and direct

Speed Responses start within a millisecond

Examples Nicotinic acetylcholine, AMPA and NMDA glutamate, GABA-A, and glycine receptors

Effect Ions flow through the open channel and change the cell's voltage right away

Ionotropic receptors carry the fast signals.

METABOTROPIC

Slower and amplified

Speed Effects take tens of milliseconds to seconds, and can last longer

Examples Dopamine D1 to D5, most serotonin receptors, mGluRs, GABA-B, and muscarinic acetylcholine receptors

Effect One bound receptor can trigger many downstream molecules, amplifying the signal

Metabotropic receptors tune and shape activity.

MANY RECEPTORS

One transmitter, many subtypes

A single transmitter often has many receptor subtypes. Serotonin alone has more than a dozen, and most are metabotropic, though one family is an ion channel. This lets a single molecule do different jobs in different places, and lets drugs target one job at a time.

Selective drugs aim at one subtype.

UNIT 10 STUDY COMPLETE

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Ready for the Fab Challenge?

You've seen how the two receptor families respond to a transmitter at different speeds and scales.