Many drugs and toxins act by inhibiting substance flow across cell membranes. Which of the following inhibits primary active transport?

Question

Many drugs and toxins act by inhibiting substance flow across cell membranes.  Which of the following inhibits primary active transport?

Quizplus · Accepted Answer

Transport of ions or molecules across cell membranes can be either passive (along the concentration gradient) or active (against the concentration gradient). The former does not require energy, while the latter utilizes energy from ATP. In primary active transport, the carrier molecules are enzymes that hydrolyze ATP (ATPases) and use the energy released to transport ions and molecules against their concentration gradients. Examples of such carriers are the Na/K ATPase, the H/K ATPase, and the Ca ATPase. Synthesis of HCl by parietal cells of the gastric mucosa is dependent on the H/K ATPase, which is known as a proton pump. This carrier transports hydrogen ions into the gastric lumen in exchange for potassium ions. Omeprazole and other proton pump inhibitors inhibit the H/K ATPase, thus decreasing the concentration of HCl in the gastric lumen. These medications are used for treatment of peptic ulcer disease, gastroesophageal reflux disease (GERD), and diseases associated with increased gastrin secretion such as the Zollinger-Ellison syndrome. (Choice A) Tetrodotoxin, a potent neurotoxin found in pufferfish, functions by blocking the voltage-gated sodium channels in nerve cell membranes. It inhibits passive transport of sodium. (Choice B) Verapamil blocks L-type calcium channels, thus inhibiting passive transport of calcium ions in cardiomyocytes. (Choice D) Lidocaine is a local anesthetic and a class IB antiarrhythmic agent that functions by blocking voltage-gated sodium channels in sensory neurons, Purkinje fibers and ventricular cells. (Choice E) Dofetilide is a class III antiarrhythmic drug that blocks passive transport of potassium, specifically the delayed outward rectifier potassium current, in cardiomyocytes leading to a prolongation of the refractory period and of the QT interval. Educational Objective: Parietal cells release hydrogen ions into the gastric lumen by means of the H/K ATPase, which requires hydrolysis of ATP and is therefore an active transport mechanism. Omeprazole and other proton pump inhibitors suppress the activity of the gastric parietal cell H/K ATPase leading to an increase in the pH of the gastric lumen.

Many Drugs and Toxins Act by Inhibiting Substance Flow Across