FIGURE 1: Highly speculative and simplified scheme comparing transporters, channels, transceptors and receptors.

In channels ion transport (red vertical rhombs) is controlled by the simultaneous opening and closing of gates (green bars). Transporters, transceptors and receptors are shown to alternate from outward- to inward-facing conformations as a result of substrate or ligand (horizontal rhombs) binding. In the scheme the C-terminal domain of receptors and transceptors is arbitrary considered to be the domain recognized, specifically in its inward topology, by the downstream effector protein (E), which transduces the relative signal.