Involvement of phosphatidylcholine-specific phospholipase C in thromboxane A₂ receptor-mediated extracellular Ca²⁺ influx in rat aorta.
An involvement of signal transduction other than phosphatidylinositol turnover in thromboxane A(2) receptor (TP receptor)-mediated vascular contraction was investigated in rat aorta. The contraction induced by U46619, a TP receptor agonist, at low concentrations (≤ 30 nM) was partially inhibited by verapamil, an inhibitor of voltage-dependent Ca(2+) channels (VDCC), and was further diminished in Ca(2+)-free solution. Twenty nanomolar of U46619 induced contraction and elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)), which were consisted of two phases; slowly developing first phase followed by quickly rising second phase. The second phase was inhibited by verapamil, and all the [Ca(2+)](i) response was abolished in Ca(2+)-free solution. The contraction and [Ca(2+)](i) elevation induced by 20 nM U46619 were not inhibited by U73122, an inhibitor of phosphatidylinositol-specific phospholipase C, or GF109203X, a protein kinase C inhibitor, but were abolished by D609, an inhibitor of phosphatidylcholine-specific phospholipase C (PC-PLC). However, D609 had no effect on those induced by 1 μM phenylephrine. The U46619-induced responses were also partially inhibited by cation channel blockers, 2-APB and LOE908. The inhibition by LOE908 was abolished in the presence of verapamil, suggesting that LOE908-sensitive cation channels lead to the activation of VDCC by depolarizing plasma membrane. In contrast, 2-APB further diminished the U46619-induced [Ca(2+)](i) elevation in the presence of verapamil. In conclusion, TP receptor stimulation is suggested to be coupled with PC-PLC. Diacylglycerol produced by PC-PLC seems to activate two types of cation channels independently of PKC, which in turn leads to VDCC-dependent and independent Ca(2+) influx, thereby eliciting contraction.
Department of Pharmacology, Graduate School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka City, Shizuoka 422-8526, Japan.
Kimiaki
K
Suzuki
Shin-ya
SY
Saito
Tomohisa
T
Ishikawa
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005110:Extracellular Space / Q000187:drug effects* / Q000378:metabolism*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism; D008297:Male; D010713:Phosphatidylcholines / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000819:agonists / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013379:Substrate Specificity; D010738:Type C Phospholipases / Q000378:metabolism*; D014661:Vasoconstriction / Q000187:drug effects
D007473:Ion Channels; D010713:Phosphatidylcholines; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D010738:Type C Phospholipases; D002118:Calcium