I N T R O D U C T I O N Chloride channels are present in the plasma membranes o f epithelia (Frizzell et al., 1981), nerve (Hamill et al., 1983), and muscle (Blatz and Magleby, 1985), as well as in intraceilular membranes such as Golgi apparatus (Glickman et al., Address reprint requests to Dr. Qais AI-Awqati, Depts. of Medicine and Physiology, College of Physicians and Surgeons, Columbia Unive...