Studies of the Contracting Mechanism Induced by Slow Reacting Substance of Anaphylaxis (SRS‐A): Interaction with Calcium

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Abstract
The Ca2+ dependency of the contractions elicited by egg albumin and SRS-A [slow-reacting substance of anaphylaxis] in isolated tracheal preparations from sensitized guinea-pigs was studied. The egg albumin contraction consisted of a rapid, initial and a long lasting, tonic phase; the first phase independent and the latter dependent of extracellular Ca2+. The SRS-A contraction was completely dependent of extracellular Ca2+ ions. The egg albumin contraction of the parenchymal strips was not influenced by extracellular Ca2+. SRS-A released Ca2+ from a microsomal fraction of sensitized lung tissue. This effect was absent in microsomes from desensitized lung tissue. The Ca2+-mobilizing effect of SRS-A is of utmost importance for the initiation of contraction of the tracheal smooth muscle.