Receptors on target cells. Receptors on airway smooth muscle.

Airway smooth muscle is a complex tissue that, in common with most other cell types, possesses a multitude of specific binding proteins that are coupled usually via guanine nucleotide regulation proteins to intracellular effector mechanisms. The development of sophisticated probes and biochemical approaches should allow an in-depth characterization of receptor subtypes, expression, regulation, and coupling to effector mechanisms that are activated as a consequence of ligand/receptor interaction. To date, most receptors in airway smooth muscle appear to be coupled via G proteins to these effector systems: PI turnover, adenylate cyclase, or phospholipase C. Qualitative and quantitative estimates of receptor proteins and the nature and efficiency of coupling to these effector mechanisms need to be linked to physiologic function and the regulation of airway smooth muscle response in health and disease.