Abstract

Receptors for the peptidyl leukotrienes, (LT)C4, LTD4 and LTE4, and the signaling pathways to which they are coupled were characterized in isolated guinea pig gastric muscle cells. The three LTs were equipotent contractile agonists (EC50 values = 0.10-0.12 nM), but they elicited their responses by interacting with distinct receptors. The contractile responses to LTD4 and LTE4, but not LTC4, were inhibited by the LTD4 antagonist, SKF 104353 [2-(S)-hydroxy-3-(R)-[(2-carboxyethyl)thiol]-3-[2-(8- phenyloctyl)phenyl]-propanoic acid]. Similar Ki estimates for SKF 104353 suggested interaction of LTD4 and LTE4 with a common receptor. Decisive evidence for distinct LTC4 and LTD4/LTE4 receptors was obtained by applying a receptor protection technique. Cells in which LTC4 was used as a receptor protective agent while other receptors were inactivated by N-ethylmaleimide retained their responses to LTC4 only. Cells in which LTD4, LTE4 or SKF 104353 were used as a receptor protective agent retained their responses to LTD4 and LTE4 only. Both LTC4 and LTD4/LTE4 receptors were coupled to Pl hydrolysis: all three LTs stimulated similar increases in inositol 1,4,5-trisphosphate (IP3) levels (3.9-4.3 pmol/10(6) cells), protein kinase C activity (85-94 pmol/mg/min) and cytosolic-free Ca++ ([Ca++]i) (278-306 nM). Contractile responses were abolished: 1) when Pl hydrolysis was inhibited by neomycin and 2) when Ca++ stores were depleted by pretreatment of muscle cells with caffeine in Ca(++)-free medium, but not when muscle cells were incubated in Ca(++)-free medium or with Ca++ channel blockers, suggesting that contraction and [Ca++]i were mediated by IP3-dependent Ca++ release.(ABSTRACT TRUNCATED AT 250 WORDS)