Final answer:
The most rapid intracellular responses are stimulated by ligand-gated channels, which immediately alter the cell membrane's permeability to ions leading to swift cellular responses.
Step-by-step explanation:
The question pertains to which type of receptor stimulates the most rapid intracellular responses. Among the options presented, ligand-gated channels are known for their quick response to stimuli because they directly alter the permeability of the cell membrane to specific ions. This leads to almost instantaneous changes in cell polarization and signaling. On the other hand, catalytic receptors (or receptor-enzymes like receptor tyrosine kinases) are involved in signaling pathways that usually have multiple steps, though they can still have a rapid onset. G-protein-coupled receptors are indeed fast but have a slightly delayed response compared to ion channels due to the need to activate G-proteins and then other downstream effectors. Integrin receptors typically mediate responses related to cellular adhesion and the extracellular matrix and are not generally associated with rapid signaling.