QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Data Supplement All Versions of this Article: jpet.107.121830v1 322/2/778    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Bilodeau, M. L. Articles by Hamm, H. E. Search for Related Content PubMed PubMed Citation Articles by Bilodeau, M. L. Articles by Hamm, H. E.

CARDIOVASCULAR

Regulation of Protease-Activated Receptor (PAR) 1 and PAR4 Signaling in Human Platelets by Compartmentalized Cyclic Nucleotide Actions

Departments of Pharmacology (M.L.B., H.E.H.) and Medicine, Division of Cardiovascular Medicine (M.L.B.), Vanderbilt University Medical Center, Nashville, Tennessee

Thrombin potently regulates human platelets by the G protein-coupled receptors protease-activated receptor (PAR) 1 and PAR4. Platelet activation by thrombin and other agonists is broadly inhibited by prostacyclin and nitric oxide acting through adenylyl and guanylyl cyclases to elevate cAMP and cGMP levels, respectively. Using forskolin and YC-1 [3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole] to selectively activate the adenylyl and guanylyl cyclases, respectively, and the membrane-permeable analogs N⁶,2'-O-dibutyryladenosine-3'-5'-cAMP (dibutyryl-cAMP) and 8-(4-parachlorophenylthoi)-cGMP (8-pCPT-cGMP), we sought to identify key antiplatelet steps for cyclic nucleotide actions in blocking platelet activation by PAR1 versus PAR4. Platelet aggregation by PAR1 or PAR4 was inhibited with similar EC₅₀ of 1.2 to 2.1 µM forskolin, 31 to 33 µM YC-1, 57 to 150 µM dibutyryl-cAMP, and 220 to 410 µM 8-pCPT-cGMP. There was a marked left shift in the inhibitory potencies of forskolin and YC-1 for -granule release and glycoprotein IIbIIIa/integrin IIb3 activation (i.e., EC₅₀ of 1–60 and 40–1300 nM, respectively) that was not observed for dibutyryl-cAMP and 8-pCPT-cGMP (i.e., EC₅₀ of 200–600 and 40–140 µM, respectively). This inhibition was essentially instantaneous, and measurements of cyclic nucleotide levels and kinase activities support a model of compartmentation involving the cyclic nucleotide effectors and regulators and the key molecular targets for this platelet inhibition. The different sensitivities of PAR1 and PAR4 to inhibition of calcium mobilization and dense granule release identify key antiplatelet steps for cyclic nucleotide actions and are consistent with the signaling models for these receptors. Specifically, PAR4 inhibition depends on the regulation of both calcium mobilization and dense granule release, and PAR1 inhibition depends predominantly on the regulation of dense granule release.

Address correspondence to: Heidi E. Hamm, Vanderbilt University Medical Center, 442 Robinson Research Building, Nashville, TN 37232-6600. E-mail: heidi.hamm{at}vanderbilt.edu