Active Transport - Podcast Version 0:00 / 0:00 1x 0.25x 0.5x 0.75x 1x 1.25x 1.5x 1.75x 2x Cell membranes are selectively permeable. This means that they allow the movement of some molecules freely across them, but do not allow the free passage of others. In broad terms, there are three ways in which molecules move across membranes. These are the processes of diffusion, osmosis and active transport. In this article, we will discuss active transport, and consider the clinical relevance of this. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Mechanism of Active Transport Active transport is the movement of molecules from an area of lower concentration to a higher concentration, i.e. up a concentration gradient, via specialised membrane proteins. As this is against the concentration gradient, it cannot occur passively. Therefore, active transport requires energy, which is provided by the breakdown of ATP. Active transport is a highly demanding metabolic process; some cells can use up to 50% of their energy on active transport alone. A key example of an active transporter is the sodium-potassium (Na/KATP-ase) pump. This exports three sodium ions in return for two potassium ions. This is key to maintaining the resting membrane potential. Co-Transport Some membrane proteins involved in facilitated diffusion or active transport can carry multiple molecules or ions at once – this is known as “co-transport”. Where the molecules move in the same direction, this is known as “symport”. Where some molecules move one way and others move the other, this is known as “anti-port”. The sodium-potassium pump is an example of an antiporter. Connectivid-D (https://commons.wikimedia.org/wiki/File:Active_Transport_Proteins.png), CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0), via Wikimedia Commons Fig 1Active transport proteins Clinical Relevance Drug Targets The sodium/potassium ATPase pump is essential to many physiological processes, so targeting it with medication can be useful clinically. Conversely, drugs which act on the pump in addition to their main action can cause unwanted side effects. Examples of drugs affecting the Na/K ATPase include: Spironolactone: An aldosterone antagonist, blocks the Na/K ATPase pump in the distal convoluted tubule and collecting duct. This reduces sodium reabsorption via the epithelial sodium channel (ENaC), and consequently reduces water reabsorption too. This is useful in heart failure and liver disease. Digoxin: This blocks Na/K ATPase, mainly in the myocardium. This leads to an accumulation of intracellular calcium, which reduces heart rate by prolonging the cardiac action potential. It also increases the force of contraction of the myocardium. This is useful in heart failure and atrial fibrillation. Steroids: Glucocorticoids have a degree of cross-reactivity at the mineralocorticoid receptor in the distal convoluted tubule/collecting duct. This increases the activity of Na/K ATPase, leading to the opposite effect of spironolactone. Over time, this leads to water retention and subsequently swelling (oedema) in these patients. Do you think you’re ready? Take the quiz below Pro Feature - Quiz Active Transport Question 1 of 3 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/3 More Questions Available Upgrade to TeachMePhysiology Pro Challenge yourself with over 2100 multiple-choice questions to reinforce learning Learn More Frequent questions What is active transport in cellular membranes? Active transport is the process of moving molecules from an area of lower concentration to a higher concentration against a concentration gradient, requiring energy from ATP. This mechanism relies on specialised membrane proteins to facilitate the movement of ions and molecules. How does the sodium-potassium pump function in active transport? The sodium-potassium pump, or Na/K ATPase, exports three sodium ions out of the cell while importing two potassium ions into the cell. This exchange is crucial for maintaining the resting membrane potential and overall cellular function. What is co-transport in the context of active transport? Co-transport refers to the simultaneous movement of multiple molecules or ions across a membrane via specific transport proteins. In this process, if the molecules move in the same direction, it is termed "symport," while movement in opposite directions is called "anti-port." How do drugs target the sodium-potassium ATPase pump clinically? Drugs can target the Na/K ATPase pump to influence various physiological processes, such as diuretics like spironolactone, which reduce sodium and water reabsorption, or digoxin, which increases intracellular calcium to improve heart function. These medications can have significant therapeutic effects in conditions like heart failure. What are the potential side effects of drugs affecting the sodium-potassium pump? Medications that act on the sodium-potassium ATPase can lead to unwanted side effects due to their impact on sodium and water balance. For instance, glucocorticoids can enhance Na/K ATPase activity, resulting in water retention and oedema, counteracting the effects of diuretics. Rate This Article