In the presence of L-NAME SERCA blockade induces endothelium-dependent contraction of mouse aorta through activation of smooth muscle prostaglandin H2/thromboxane A2 receptors

摘要

class="enumerated" style="list-style-type:decimal">The mechanism of transient contractions induced by the sarcoplasmic–endoplasmic reticulum calcium ATPase (SERCA) blocker cyclopiazonic acid (CPA) in the presence of L-NAME was investigated in mouse aorta.The contractions elicited by 10 μM CPA required an intact endothelium, were dependent upon external Ca²⁺ and were prevented by 10 μM indomethacin, the inhibitor of prostaglandin synthesis, or 1 μM SQ29548, the specific prostaglandin H2/thromboxane A2 (PGH2/TXA2) receptor blocker.A blocker of receptor/store operated Ca²⁺ channels and voltage gated calcium channels (VGCC), SK&F 96365 (10 μM), completely abolished the contractions, while a specific blocker of VGCC nifedipine (1 μM) inhibited them by one third.Dichlorobenzamyl hydrochloride, a blocker of Na⁺/Ca²⁺ exchange effectively prevented return of tension to baseline value.At higher concentrations (30–100 μM) CPA induced indomethacin-resistant tonic contractions of mouse aorta. The CPA dose response curve for tonic contractions is shifted to the right compared to the transient contractions suggesting that smooth muscle is less sensitive to CPA than endothelium.PGH2/TXA2 receptors in mouse aorta are highly sensitive to the thromboxane analogue U46619 (EC50 : 1.93 nM). This compound stimulates contractions even in the absence of external Ca²⁺, which are abolished by the Rho-kinase inhibitor HA-1077.The results suggest that 10 μM CPA induced capacitive Ca²⁺ entry in endothelial cells stimulating the release of PGH2/TXA2, which subsequently caused smooth muscle contraction dependent on Ca²⁺ influx and myofilament sensitization by Rho-kinase. Higher concentrations of CPA (30–100 μM) directly induced contraction of mouse aortic smooth muscle.