Balanced Salt Solution in Animal Tissue Culture

BALANCED SALT SOLUTIONS IN ANIMAL TISSUE CULTURE

A balanced salt solution (BSS) is composed of inorganic salts and may include sodium bicarbonate and in some cases, glucose. The compositions of some common balanced salt solutions are given in HEPES buffer (5–20 mM) may be added to these solutions if necessary and the equivalent amount of NaCl omitted to maintain the correct osmolality. BSS forms the basis of many complete media, and commercial suppliers will provide Eagle’s MEM with Hanks’s salts or Eagle’s MEM with Earle’s salts, indicating which BSS formulation was used; Hanks’s salts would imply the use of sealed flasks with a gas phase of air, whereas Earle’s salts would imply a higher bicarbonate concentration compatible with growth in 5% CO².

BSS is also used as a diluent for concentrates of amino acids and vitamins to make complete media, as an isotonic wash or dissection medium, and for short incubations up to about 4 h (usually with glucose present). BSS formulations are often modified - for instance, by omitting glucose or phenol red from Hanks’s BSS or by leaving out Ca²⁺ or Mg²⁺ ions from Dulbecco’s PBS. PBS without Ca²⁺ and Mg²⁺ is known as PBS Solution A.

The choice of BSS is dependent on both the CO² tension and the intended use of the solution for tissue disaggregation or monolayer dispersal; in these cases Ca²⁺ and Mg²⁺ are usually omitted, as in Moscona’s calcium- and magnesium-free saline (CMF) or D-PBSA. The choice of BSS also is dependent on whether the solution will be used for suspension culture of adherent cells. S-MEM, based on Eagle’s Spinner salt solution, is a variant of Eagle’s minimum essential medium that is deficient in Ca²⁺ in order to reduce cell aggregation and attachment. HBSS, EBSS, and PBS rely on the relatively weak buffering of phosphate, which is not at its most effective at physiological pH.

HEPES (10–20 mM) is currently the most effective buffer in the pH 7.2–7.8 range, and Tricine in the pH 7.4–8.0 range, although both tend to be expensive if used in large quantities.

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