Ac

ATP cAMP

Gustducin a subunit activates adenylyl cyclase (AC) of the apical membrane, raising [cAMP].

Taste cell

Basolateral membrane

PKA, activated by cAMP, phosphorylates a K+ channel in the basolateral membrane, causing it to close. The reduced efflux of K+ depolarizes the cell.

Taste cell

FIGURE 12-37 Transduction mechanism for sweet tastants.

systems, the final output is an activated protein kinase that regulates some cellular process by phosphorylating a protein critical to that process. In sensory neurons, the output is a change in membrane potential and a consequent electrical signal that passes to another neuron in the pathway connecting the sensory cell to the brain.

All these systems self-inactivate. Bound GTP is converted to GDP by the intrinsic GTPase activity of G proteins, often augmented by GTPase-activating proteins (GAPs) or RGS proteins (regulators of G-protein signaling). In some cases, the effector enzymes that are the targets of G protein modulation also serve as GAPs.

Vasopressin Epinephrine

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