Cellular carriers erythrocytes

Cellular Carriers. Erythrocytes, leukocytes, platelets, islets, hepatocytes, and fibroblasts have all been suggested as potential carriers for drugs and biological substances. They can be used to provide slow release of entrapped drugs in the circulatory system, to deliver drugs to a specific site in the body, as cellular transplants to provide missing enzymes and hormones (in... 

Since erythrocytes, platelets, and leukocytes have received the greatest attention, the discussion that follows will be limited to these carriers. Fibroblasts [180] and hepatocytes [181] have been specifically used as viable sources to deliver missing enzymes in the management of enzyme-deficiency diseases, whereas islets are useful as a cellular transplant to produce insulin [182,183],... 

Blood is the transport medium of the body. Plasma, which accounts for approximately 60% of the total volume, carries a wide range of small and medium-sized metabolites some are simply dissolved in solution (93% of the plasma is water), others are carried by specific carrier proteins. The chemical composition of the plasma is complex and reflects the chemical composition inside cells, which is why blood tests are so commonly used in diagnosis to see the biochemical events occurring in tissues. The formed cellular elements of the blood perform several functions defence against blood loss from bleeding (platelets, also called thrombocytes), defence against infection and immune surveillance (white cells, leucocytes), and gas transport and pH buffering (red cells, erythrocytes). 

Choline is an interesting example of a molecule dependent, for its cellular uptake, on facilitated diffusion. Unable, because of its permanently ionized and poorly lipophilic nature, to penetrate by simple diffusion through a Type 1 membrane, choline is rapidly transported into erythrocytes and several other kinds of cell by a specific carrier. Tetramethylammonium cations can also enter cells on this carrier, a facility denied to higher homologues which can, however, block the physiological uptake of choline (Martin, 1969). 

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