Which statement about receptor types is correct?

The statement about receptor types that is correct highlights the role of ligand-gated ion channels in altering the permeability of the cell membrane to ions. When a ligand, such as a neurotransmitter, binds to these channels, they undergo a conformational change that allows specific ions to flow into or out of the cell. This change in ion permeability can lead to significant physiological effects, such as depolarization or hyperpolarization of the cell membrane, thereby playing a crucial role in processes such as synaptic transmission in neurons.

In contrast, intracellular receptors typically interact with hydrophobic messengers, such as steroid hormones, which can easily pass through cell membranes due to their lipid-soluble nature. Receptor enzymes are focused on catalyzing reactions within the cell rather than activating extracellular enzymes. Lastly, G protein-coupled receptors primarily engage with hydrophilic messengers, which cannot cross the membrane directly; instead, they depend on secondary messengers to propagate signals inside the cell. Thus, the unique functionality of ligand-gated ion channels in changing membrane ion permeability distinctly supports the accuracy of the correct statement.