Responses of the longitudinal muscle and the muscularis mucosae of the rat duodenum to adenine and uracil nucleotides

Abstract

1 Previous studies have shown that the rat duodenum contains PI and P2y purinoceptors via which it relaxes to adenosine and adenosine 5'-triphosphate (ATP) respectively. It has also been shown to contract to uridine 5'-triphosphate (UTP) and adenosine 5'-O-(3-thiotriphosphate) (ATP-y-S), and based on their differential inhibition by the P2 antagonist suramin it has been suggested that they act via two separate receptors. In addition, the rat duodenum has been shown to dephosphorylate ATP rapidly via ectonucleotidases and adenosine deaminase. In this study the responses of two preparations from the rat duodenum, the longitudinal muscle and the muscularis mucosae, were investigated using a series of nucleotides and suramin. 4 Suramin (1 mM) inhibited relaxations induced by ATP on the longitudinal muscle, shifting the relaxation concentration-response curve to the right. This further supports the presence of a P2Y-purinoceptor on this muscle layer. Suramin (1 mM) inhibited contractions induced by AMPCPP, but not those induced by ATP, UTP or ATP-y-S, in the muscularis mucosae. Desensitization of the muscularis mucosae was seen with AMPCPP, but not with UTP or ATP-y-S, and no cross-desensitization between AMPCPP and UTP or ATP-y-S was observed. This suggests there are two receptors which mediate contraction on the rat duodenum muscularis mucosae, one suramin-sensitive and the other suramininsensitive.5 ATP was rapidly degraded by the muscularis mucosae to ADP, adenosine 5'-monophosphate (AMP) and inosine, with no adenosine being detected. A similar rate of degradation was seen for UTP with UDP, uridine 5'-monophosphate (UMP) and uridine being formed and for 2-MeSATP with 2-methylthioadenosine 5'-diphosphate (2-MeSADP), 2-methylthioadenosine 5'-monophosphate (2-Me-SAMP) and 2-methylthioadenosine being formed. AMPCPP and ATP-y-S were both degraded more slowly, AMPCPP being degraded to AMPCP, and ATP-y-S to ADP, AMP and inosine. Suramin (1 mM), did not significantly affect the rate and pattern of degradation of these nucleotides, apart from AMPCPP which was degraded slightly more slowly in the presence of suramin. 6 These results show that there is a P2y-purinoceptor which mediates relaxation in the rat duodenum longitudinal muscle. They also show that there is a contraction-mediating suramin-sensitive receptor on the rat duodenum muscularis mucosae which is desensitized by AMPCPP, and thus is probably of the P2X subtype. In addition, there is a contraction-mediating suramin-insensitive receptor on the rat duodenum muscularis mucosae which is not desensitized by UTP or ATP-y-S, and at which ATP and UTP show equal potency, and is thus probably of the P2u subtype. In addition, the rat duodenum muscularis mucosae contains ectonucleotidases and adenosine deaminase, which rapidly degrade nucleotides, although the inhibition by suramin of this degradation is unlikely to explain the differential antagonism by suramin of the nucleotides.

Calcium oscillations induced by ATP in human umbilical cord smooth muscle cells

“…Suramin is the most common antagonist for P 2 receptors, can effectively block P 2Y1 , P 2Y2 , P 2Y11 , P 2Y12 (Johnson et al, 1996; Charlton et al, 1996a, 1996b) and P 2Y13 (von Kugelgen, 2006). Suramin is less effective in blocking P 2Y6 , which is widely distributed in heart, blood vessel and brain (Johnson et al, 1996) and has no effect on P2Y4 (Communi et al, 1996) even at high dosage (30–100 µM) (Wildman et al, 2003), which are expressed in placenta and epithelia. Therefore, suramin does not block all P 2Y receptors with equal efficacy and from the available data we suggest that P 2Y4 receptors are functional expressed in HUCASMC.…”

Peripheral Nervous System

“…The general consensus is that: (a) The P2 receptors in intestinal smooth muscle mediating NANC inhibitory transmission are probably P2Y 1 receptors (Wang et al 2007;Gallego et al 2008a). a,b-MeATP has a potent relaxant action in some preparations (Johnson and Hourani 1994;Johnson et al 1996;Pacaud et al 1996). Alternatively, it may be that a,b-meATP is acting on P2X receptors (Storr et al 2000;De Man et al 2003), probably P2X 1 , P2X 2/3 or P2X 3 receptors on nerve varicosities to release ATP which then acts on P2Y 1 receptors on smooth muscle to cause relaxation (see King and Townsend-Nicholson 2008, in the section on taenia coli).…”

“…Human small intestinal muscle contains appreciable levels of mRNA for the P2Y 6 receptor (Communi et al 1996). (b) The P2 receptors mediating smooth muscle contractions, at least in guinea pig and in the small intestine of most lower vertebrates (Burnstock 1969;Sneddon et al 1973) (perhaps in response to ATP released by NANC excitatory nerves) are probably also P2Y receptors, perhaps P2Y 2 or P2Y 4 , since they are activated by UTP as well as by ATP (Johnson and Hourani 1994;Kennedy and Humphrey 1994;Windscheif et al 1995;Johnson et al 1996). (c) There is evidence that ATP mediates the non-cholinergic component of the EJP and contraction of intestinal smooth muscle (Zagorodnyuk and Maggi 1998) and a,bmeATP-induced ileal contractions were inhibited in P2X 1 receptor knockout mice (Vial and Evans 2001).…”

A contraction-mediating receptor for UTP, presumably P2Y2, in rat vas deferens

“…Uridine 5'-triphosphate (UTP) and uridine 5'-diphosphate (UDP), for instance, elicit contraction of a variety of vascular and non-vascular smooth muscle preparations (for rat tissues see Sakai et al 1979;Ralevic and Burnstock 1991;Juul et al 1992;Hourani et al 1993;Bolego et al 1995;García-Velasco et al 1995;Eltze and Ullrich 1996;Johnson et al 1996;Otsuguro et al 1996;Rubino and Burnstock 1996;McLaren et al 1998). In several tissues, the site of action of these pyrimidine nucleotides appears to be a receptor which is also activated by ATP and related purine nucleotides (e.g., Hourani et al 1993;Johnson et al 1996;Rubino and Burnstock 1996); in some tissues, however, UTP and UDP activate receptors apparently insensitive to purine nucleotides (e.g., Ralevic and Burnstock 1991;Juul et al 1992). Among the recombinant nucleotide P2-receptors presently known (see Harden et al 1998;Humphrey et al 1998), the G-protein-coupled P2Y subtypes P2Y 2 , P2Y 4 and P2Y 6 are possible sites of action of the uracil nucleotides; P2Y 1 and the recombinant P2X subtypes, which represent ligand-gated cation channels, are almost unresponsive to UTP.…”