Mechanisms of contraction induced by partially purified slow reacting substance from human polymorphonuclear leukocytes and leukotriene D in guinea pig ileal smooth muscle

On the basis of the experiments described here, we suggest that the mechanism of action of SRS in guinea pig ileal longitudinal muscle is very similar to that used by other agonists in this preparation, namely interaction at a specific receptor to activate Ca⁺⁺ channels leading to Ca⁺⁺ influx and mechanical response. SRS responses differ in 1 important respect from those produced by other agonists. SRS and leukotriene D cause the generation of a slower contraction, which has a greater resistance to reversal by washing. The basis for this unique and prolonged duration of action is unknown but may represent an exceptionally tight, or even irreversible, association with a membrane component. Current studies on the structure of SRS may be helpful in this regard. Although not definitive, this report clearly indicates that a SRS 'receptor' is, in fact, present on smooth muscle and that it utilizes a pool of calcium channels common to all smooth muscle agonists.