Growth of Animal Cells in Culture

Animal cell culturing is more difficult than microbial culturing because animal cells demand more nutrients and should be attached to specially coated surfaces for their growth. Still there are various undifferentiated and differentiated animal cell types which have been cultured.

The nine amino acids, known as the essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine), are not synthesised by adult vertebrate animals and therefore must be obtained from external sources.

Apart from these, most of the cultured cells require cysteine, glutamine, and tyrosine also, synthesised by the intact animal cell, e.g., liver cells synthesise tyrosine from phenylalanine; liver and kidney cells synthesise glutamine. All animal cells both within the organism and in culture can synthesise the remaining eight amino acids; therefore these amino acids need not be present in the diet or culture medium.

Other essential components of media of the animal cell culture are vitamins (cannot make at all or in adequate amounts), various salts, glucose, serum, and the non-cellular part of the blood.

Most of the cultured animal cells require special solid surfaces for growth. Within the intact animal tissues, the cells are tightly packed and interact with other cells through the cellular junctions. The cells are also in contact with the extracellular matrix (a complex network made up of secreted proteins and carbohydrates to fill the intercellular spaces).

The constituents of matrix secreted by the cells participate in binding the cells in tissues together; as well as it also provides a lattice through which cells can move, especially at the early phase of animal differentiation.

In various animal tissues, the extracellular matrices consist of several common components:

  1. Fibrous collagen proteins,
  2. Hyaluronic acid,
  3. A large mucopolysaccharide,
  4. Covalently linked polysaccharides,
  5. Proteins in the form of proteoglycans (mostly carbohydrate), and
  6. Glycoproteins.

The exact matrix composition is different in different tissues, thus giving a specialised function to each tissue. For example, the extracellular matrix in connective tissue mainly contains a type of collagen protein which forms insoluble fibres exhibiting a very high tensile strength. Fibroblasts, the major cells of connective tissue, secrete this type of collagen and other components of the matrix.

Receptor proteins present on the plasma membrane of a cell bind various matrix elements, and provide strength and rigidity.

Given below are the conditions need to be maintained for the growth of animal cells:

Balanced Salt Solution (BSS): It is made up of inorganic salts which maintain the osmotic pressure and buffer medium at physiological pH. Some inorganic ions, e.g., Na+,K+,Mg2+,Ca2+,Cl,SO42+,PO43+, etc., are also required to stimulate the process growth.

Buffering Systems: These are required to compensate for CO2 evolution and lactic acid production from carbohydrate metabolism. Bicarbonates are used as a buffer for the media.

pH: Neutral pH value (i.e., 7) is considered to be optimum for the growth of cells. It facilitates inspection and control of cultures.

Energy Sources: The major source of energy is carbohydrates which initiate growth in cultured cells. The most commonly used sugar is glucose; while others like maltose, sucrose, fructose, galactose, and mannose are also used.

Amino Acids: Arginine, cysteine, histidine, isoleucine, lysine, etc., are the essential amino acids required for the growth of most animal cells.

Vitamins: Biotin, choline, folic acid, nicotinic acid, panthoic acid, pyridoxal, riboflavin, thiamine, and inositol are some of the vitamins required for the growth and multiplication of animal cells.

Hormones and Growth Factors: Hormones and growth factors are essential for a variety of different effects on the survival and proliferation of cells. Insulin and hydrocortisone are the most commonly used ones. Also, interleukins, colony stimulating factors, epidermal growth factor, and fibroblast growth factor are required.

Proteins and Peptides: Fetuin, fibronectin, albumin, and transferrin are the protein supplements commonly used for stimulating animal cell proliferation and growth.

Fatty Acids and Lipids: These are important components of some serum-free media, but their effect has not been yet established.

Accessory Factors: Some additives like iron, zinc, copper, and selenium trace elements also aid in effective cell growth.

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Santhakumar Raja

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