Characterization of the binding of diadenosine 5′,5‴-P1,P4-tetraphosphate (Ap4A) to rat liver cell membranes

Abstract

Diadenosine polyphosphates present in the extracellular environment can, through interaction with appropriate purinoceptors, influence a range of cellular activities. Here we have investigated the nature of the ligand:receptor interactions involved in diadenosine 5',5'''-P1, P4-tetraphosphate (Ap4A)-mediated stimulation of glycogen breakdown in isolated rat liver cells. [2-3H]Ap4A showed specific binding to both intact isolated liver cells and plasma membrane fractions prepared from isolated liver cells. HPLC analysis confirmed that binding was mediated by intact Ap4A and not by potential breakdown products (e.g. ATP, adenosine, etc.). Binding of [2-3H]Ap4A, to isolated liver cell plasma membrane preparations, was successfully displaced by a range of both naturally occurring and synthetic diadenosine polyphospates with the rank order potency Ap4A > or = Ap5A > Ap6A > Ap3A > Ap2A. [2-3H]Ap4A binding was not displaced by P1 effectors but was successfully displaced by a range of P2 effectors with the rank order potency 2-methylthio-ATP > ATP > ATP > or = adenosine 5'-[alpha beta-methylene]triphosphate > adenosine 5'-[beta gamma-methylene]triphospate. These findings are consistent with the interaction of Ap4A with a P2y-like subclass of purinoceptor and are discussed in relation to (1) the known purinoceptor populations in liver cell plasma membranes and (2) observations concerning the binding of diadenosine polyphosphates to purinoceptors in other tissues.

Diadenosine polyphosphates in insulin-secreting cells: interaction with specific receptors and degradation.

“…Therefore, a specific diadenosine polyphosphate receptor could be involved. Binding sites for diadenosine polyphosphates have been shown in various cells, such as heart (5,6), brain (7,8), and liver (9). In some cases, binding sites resemble adenosine receptors (heart [6]) or either adenosine or P 2 receptors (guinea pig vas deferens [25], follicular oocytes [26], heart [27], kidney [28]).…”

“…Some of them are suggested to be involved in blood pressure regulation (1)(2)(3) or even to be important for the development of essential hypertension (4). Binding sites for various diadenosine polyphosphates have already been shown in various cells, such as heart (5,6), brain (7,8), and liver (9).…”

T4 DNA ligase synthesizes dinucleoside polyphosphates

“…Ap1A and other dinucleoside polyphosphates are present in chromaffin granules of bovine adrenal medulla [10][11][12], in synaptic terminals [13] and in human blood platelets [14]. After an appropriate stimulus they are released from these storage sites to the blood and through their interaction with some still not well defined purine receptors [15][16][17][18][19] they may modulate a variety of processes such as vascular tone [20], platelet aggregation [20,21], neurotransmission [22], cell proliferation [3,7,23], etc.…”

A peptide isolated from a random phage peptide library is a structural mimic to the P1, P4‐diadenosine 5′‐tetraphosphate binding site on its receptor

“…Other investigators have demonstrated the presence on rat brain synaptosomes of a P 2D purinoceptor [18]. In chromaffin cells and hepatocytes, Ap 4 A appears to interact with P 2Y purinoceptors [17,19]. These data suggest that Ap 4 A may interact with a heterogeneous population of receptors.…”

“…The presence of Ap 4 A receptors has been demonstrated on cardiac myocytes [16], on chromaffin cells [17], on brain synaptosomes [18], and on hepatocytes [19]. However, the nature of the receptor involved in Ap 4 A-mediated cellular signaling is unclear.…”