Figure 1.

Suggested structure of a transducon on the plasma membrane. In the K⁺-transporting mode, (a), the major constituents remain bound together, except for calmodulin. When a ligand binds to the receptor (b), it is suggested that the receptor and G_αa subunit from a G protein remain bound together, briefly activating the Ca²⁺ channel. The B subunit of calcineurin situated at the Ca²⁺ channel mouth responds to the high Ca²⁺ concentrations and activates the A subunit. Dephosphorylation inhibits the K⁺ channel, and dephosphorylation of the Ca²⁺ channel prolongs opening. Calmodulin binds to the ATPase regulating Ca²⁺ outflow from the cell but only at a suitable distance from the channel mouth and where Ca²⁺ concentrations are lower.