ABSTRACT
Nociceptive primary afferents have the capacity to induce a state of increased excitability in the dorsal horn neurons of the spinal cord. It is well accepted that capsaicin-sensitive C-fibers transduce noxious stimulation and acute pain and that capsaicin-insensitive A beta-fibers are responsible for touch and innocuous sensation. It has been reported that the intrathecal (i.t.) administration of prostaglandin F(2 alpha) (PGF(2 alpha)) and ATP induces mechanical allodynia via the capsaicin-insensitive primary afferent pathway. In the present study, we investigated the interaction of purinoceptor P2X and the PGF(2 alpha) receptor (FP) in the induction of allodynia by use of mice lacking FP (FP(-/-)). Both PGF(2 alpha) and the P2X receptor agonist alphabeta-methylene ATP administered i.t. strongly induced allodynia for 50 min by tactile stimuli to the flank of mice. The allodynia induced by alphabeta-methylene ATP, but not that by PGF(2 alpha), was suppressed by simultaneous i.t. administration of P2X receptor antagonists pyridoxalphosphate-6-azophenyl-2,4-disulphonic acid and A-317491. In contrast, the allodynia induced by alphabeta-methylene ATP as well as that by PGF(2 alpha) was not observed in FP(-/-) mice. Immunostaining of beta-galactosidase, a reporter knocked into the endogenous FP locus in FP(-/-) mice, showed that the FP receptor was co-localized with P2X(2) and P2X(3) receptors in neurons of the spinal cord. alphabeta-Methylene ATP evoked a transient or sustained [Ca(2+)](i) increase in most of the PGF(2 alpha)-responsive cells in the deeper layer of the spinal cord, and the alphabeta-methylene ATP-evoked increase was blocked by the FP receptor antagonist AL-8810 in two-thirds of the cells. Neither PGF(2 alpha) nor alphabeta-methylene ATP induced the activation of spinal microglia. The present study demonstrates that the alphabeta-methylene ATP-evoked allodynia is mediated by the FP receptor, possibly via the functional coupling between the activation of P2X(2/3) receptors on the central terminal of capsaicin-insensitive fibers and FP receptors on spinal neurons.
Subject(s)
Adenosine Triphosphate/metabolism , Hyperalgesia/metabolism , Nociceptors/metabolism , Pain/metabolism , Receptors, Prostaglandin/metabolism , Receptors, Purinergic P2/metabolism , Adenosine Triphosphate/analogs & derivatives , Adenosine Triphosphate/pharmacology , Afferent Pathways/drug effects , Afferent Pathways/metabolism , Animals , Calcium Signaling/drug effects , Calcium Signaling/physiology , Dinoprost/analogs & derivatives , Dinoprost/pharmacology , Galactosides/analysis , Galactosides/metabolism , Genes, Reporter , Hyperalgesia/chemically induced , Hyperalgesia/physiopathology , Indoles/analysis , Indoles/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Nociceptors/drug effects , Pain/chemically induced , Pain/physiopathology , Posterior Horn Cells/drug effects , Posterior Horn Cells/metabolism , Presynaptic Terminals/drug effects , Presynaptic Terminals/metabolism , Purinergic P2 Receptor Agonists , Purinergic P2 Receptor Antagonists , Receptors, Prostaglandin/drug effects , Receptors, Prostaglandin/genetics , Receptors, Purinergic P2X2 , Receptors, Purinergic P2X3 , Spinal Nerve Roots/drug effects , Spinal Nerve Roots/metabolismABSTRACT
The N-terminal 28-residue peptide of actin whose Cys10 was labeled with 5-iodoacetamido-fluorescein (F3K peptide) was isolated from the fluorescently labeled thrombin digest of actin. The effect of myosin subfragment 1 (S1) on the fluorescence of F3K peptide was examined in the absence of ATP. With increasing concentration of S1 added, the fluorescence intensity of F3K peptide increased by maximally 7.3% with an apparent dissociation constant of 5.7 microM, suggesting a role of this peptide region of actin in acto-S1 binding in rigor. F3K peptide was crosslinked with S1 at 10 mM NaCl using a zero-length crosslinker by the method of Grabarek and Gergely [Anal. Biochem. 185, 131-135 (1990)]. The crosslinking was greatly inhibited by the presence of either 0.2 M NaCl or 5 mM MgATP. The analyses of amino acid compositions and sequences of the fluorescent peptides isolated from a lysylendopeptidase digest of the crosslinked S1 indicated that F3K peptide was mainly crosslinked to residues 637-642 of the S1 heavy chain. The crosslinked S1 was isolated by selectively pelleting the uncrosslinked S1 with F-actin. ATPase activity of the isolated crosslinked S1 alone was twice as high as that of control S1. The actin-activated ATPase activity of the crosslinked S1 was much lower than that of uncrosslinked S1. The estimated Vm and Km values were 1.72 s-1 and 125 microM, respectively. The Vm decreased to less than 1/8, while Km increased only twofold. The results suggest that the N-terminal 28-residue segment of actin may be implicated in the rigor binding of actomyosin and in the actin-activation of myosin ATPase, but may not be the main determinant of actomyosin binding in the presence of ATP.