VPT 311: General and Systemic Veterinary Pharmacology (2+1)

CARRIER MEDIATED TRANSPORT

• In Carrier mediated transport, the drug combines with a carrier present in the membrane and the complex then translocates from one side of the membrane to the other.
• The carriers for polar molecules appear to form a hydrophobic coating over the hydrophyllic groups and thus facilitate passage through the membranes. Substances permitting transit of ions across membranes are called ionophores.
• Carrier transport is specific, saturable and competitively inhibited by analogues that utilise the same carrier. Intestinal absorption sometimes depends on carriermediated transport. 
• Examples of carrier mediated transport are: 
• levodopa is taken up by a carrier that normally transports phenylalanine;
• flurouracil is transported by the system that carries natural pyrimidines;
• iron is absorbed via a specific carrier on the surface of the mucosal cells in the jejunum and
• calcium is absorbed by means of a vitamin D dependent carrier system.
• This carrier mediated transport is of two types, namely
  • facilitated diffusion and
  • active transport