What is a characteristic of ionotropic receptors?

Ionotropic receptors are characterized by their rapid response to neurotransmitter binding and their direct association with ion channels. When a neurotransmitter binds to an ionotropic receptor, it causes a conformational change in the receptor that opens the ion channel embedded in the same protein complex. This allows specific ions to flow across the cell membrane, leading to immediate changes in the membrane potential, such as depolarization or hyperpolarization. This mechanism underlies the fast signaling typically observed in synaptic transmission, making ionotropic receptors crucial for quick communication between neurons.

The defining feature of ionotropic receptors is their ability to mediate fast synaptic transmission, in contrast to other types of receptors such as metabotropic receptors, which involve slower and more complex signaling pathways that often use second messengers. As such, options describing slow or indirect mechanisms or reliance on secondary messengers do not accurately capture the innate function of ionotropic receptors.