Diadenosine Polyphosphate Analog Controls Postsynaptic Excitation in CA3-CA1 Synapses via a Nitric Oxide-Dependent Mechanism

Abstract

Previously, we have described the modulatory effect of diadenosine polyphosphates Ap 4 A and Ap 5 A on synaptic transmission in the rat hippocampal slices mediated by presynaptic receptors (Klishin et al., 1994). In contrast, we now describe how nonhydrolyzable Ap 4 A analog diadenosine-5Ј,5ٞ-P 1 ,P 4 -[␤,␤Ј-methylene]tetraphosphate (AppCH 2 ppA) at low micromolar concentrations exerts strong nondesensitizing inhibition of orthodromically evoked field potentials (OFPs) without affecting the amplitude of excitatory postsynaptic currents and antidromically evoked field potentials, as recorded in hippocampal CA1 zone. The effects of AppCH 2 ppA on OFPs are eliminated by a P2 receptor antagonist pyridoxal-phosphate-6-azophenyl-2Ј,4Ј-disulfonic acid (PPADS) but not mimicked by purinoceptor agonists ␣,␤-methylene-ATP and adenosine 5Ј-O-(3-thio)-triphosphate, indicating that a P2-like receptor is involved but not one belonging to the conventional P2X/P2Y receptor classes. Diadenosine polyphosphate receptor (P4) antagonist Ip 4 I (diinosine tetraphosphate) was unable to modulate AppCH 2 ppA effects. Thus, the PPADS-sensitive P2-like receptor for AppCH 2 ppA seems to control selectively dendritic excitation of the CA1 neurons. The specific nitric oxide (NO)-scavenger 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide is shown to significantly attenuate AppCH 2 ppA-mediated inhibitory effects, indicating that NO is involved in the cascade of events initiated by AppCH 2 ppA. Further downstream mediation by adenosine A1 receptors is also demonstrated. Hence, AppCH 2 ppA-mediated effects involve PPADS-sensitive P2-like receptor activation leading to the production of NO that stimulates intracellular synthesis of adenosine, causing in turn postsynaptic A1 receptor activation and subsequent postsynaptic CA1 dendritic inhibition. Such spatially selective postsynaptic dendritic inhibition may influence dendritic electrogenesis in pyramidal neurons and consequently mediate control of neuronal network activity.

Stable, synthetic analogs of diadenosine tetraphosphate inhibit rat and human P2X3 receptors and inflammatory pain

“…AppNHppA and AppCH 2 ppA were prepared using LysU-mediated synthetic–biosynthetic (chemo-enzymatic) procedures as described previously 42,43 with rigorous purification by high-performance liquid chromatography. 44,45…”

P2x3-receptor desensitization as an alternative mechanism of analgesia

“…На відміну від ендогенних ApnAs, синтезовані аналоги можуть бути виготовлені з модифікаціями, які дають змогу уникнути дуже високої гідролізувальної активності різноманітних нуклеаз. Так, аналог діаденозинового поліфосфата, що не гідролізується AppCH2ppA, в якому оксомости було замінено на карбогенові, показав анальгетичні властивості у деяких моделях болю [36]. Нещодавно синтезований аналог, що не гідролізується, з азотним залишком (AppNH2ppA) спричинив пригнічення a,b-meАТФ-індукованого Р2Х3-рецепторопосередкованого струму, діючи саме через процес високоафінної десенситизації.…”

“…Цей ліганд має невеликий потенціюючий ефект на АТФ-струми, але, що важливо, надзвичайно пригнічує Р2Х3-рецепторопосередковані струми, впливаючи тільки на десенситизований рецептор. Алостеричний механізм дії пуротоксину полягає в уже відомому процесі «замороження» десенситизації за допомогою приєднання до високоафінного сайта зв'язування [22,36,27].…”

Diadenosine-Polyphosphate Analogue AppCH2ppA Suppresses Seizures by Enhancing Adenosine Signaling in the Cortex

“…For many years there has been an interest in diadenosinepolyphosphates (Ap n A, where n is 2-7), as natural extracellular and intracellular signaling molecules present in the brain (Pintor et al 1993;Baxi and Vishwanatha 1995;Miras-Portugal et al 1999) that can regulate neuronal activity through activation of purinergic P2X and P2Y receptors (Pintor et al 1993(Pintor et al , 1996Lazarowski et al 1995;Pintor and Miras-Portugal 1995;Schachter et al 1996;Wildman et al 1999). We previously showed that a stable analogue of diadenosine-tetraphosphate, known as β, β′-methylene diadenosine 5′,5″′-P 1 , P 4 -tetraphosphate (AppCH 2 ppA) selectively modulates the excitability of hippocampal CA1 pyramidal neurons (Melnik et al 2006). We hypothesized that such a nonhydrolysable compound might exert targeted antiepileptic actions by an adenosine-dependent mechanism.…”