Adenosine(5′)hexaphospho(5′)adenosine stimulation of a Ca²⁺‐induced Ca²⁺‐release channel from skeletal muscle sarcoplasmic reticulum

Abstract

Stimulation of a Ca2 +-induced Ca2 +-release channel from skeletal muscle sarcoplasmic reticulum by various adenosine(5')oligophospho(5')adenosines (Ap.A, n --2 -6) by a rapid quenching technique using radioactive calcium was studied. Ap4A, Ap5A and Ap6A, as well as adenosine S'-[B,ymethyleneltriphosphate (AdoPP [CH2]P), a non-hydrolyzable ATP analogue, stimulated the Ca2 +-release channel, whereas ApzA and Ap3A had no effect. At a concentration of 0.5 mM, the order of stimulation was AdoPP[CH,]P < Ap4A < Ap,A -4 Ap,A. As well as having the hlghest affinity (0.44 mM for half-maximal stimulation), Ap6A showed an extraordinarily high Hill coefficient of 3.3 (1.9 for AdoPP[CH2]P, 2.1 for Ap,A). The stimulating effect of Ap6A was reversible, yet its dissociation proceeded very slowly. Stimulation of Ca2+ release by Ap6A was counteracted by Mgz+ and ruthenium red. A 2',3'-dialdehyde derivative of Ap6A, which is a chemical probe for amino groups, stimulated irreversibly the Ca2 +-release channel and modified some high-molecular-mass sarcoplasmic reticulum proteins, possibly including the channel protein. Our data suggest that Ap6A stimulates the Ca2 + channel by binding to the activation site of the channel subunit and simultaneously preventing the spontaneous decay of the Ca2+ channel by keeping together two of the four channel subunits by bridging them with its two adenosine groups.The sarcoplasmic reticulum (SR) is the main Caz+-storage site in skeletal muscle cells and plays a central role in Ca2+ regulation during the contraction/relaxation cycle [l -31. Ca2 + release from the SR is triggered by plasma and T-tubule membrane depolarization. The molecular mechanism of Ca2 + release is not well understood.

AMP is a partial agonist at the sheep cardiac ryanodine receptor

“…As such large dierences in the activity of the adenine nucleotides can be achieved by the removal or addition of a single phosphate group, electrostatic interactions between the phosphates and the amino acid residues in the binding sites may play an important role in determining the ability of a ligand to bind to and activate the channel. This is supported by results from Ca 2+ -¯ux and [ 3 H]-ryanodine binding experiments using various diadenosine polyphosphate (Ap n A) compounds (Holden et al, 1996;Morii & Makinose, 1992) where the more phosphates separating the two adenosine moieties, the more eective and potent the compound. 2+ from 10 to 65 mM.…”

Identification of a serine protease which activates the mouse heart adenosine 5',5''',P1,P4-tetraphosphate receptor

“…It has been shown that A p A inhibits ADP-induced platelet aggregation (Zamecnik et al, 1992;Busse et al, 1988;Harrison et al, 1975) and influences smooth muscle tone of isolated rabbit arteries (Pohl et al, 1987;Luthje & Ogilvie, 1987). In addition, Ap4A has been shown to increase basal secretion of catecholamines from isolated chromaffin cells (Casto et al, 1990), elicit excitation of the rat nodose ganglion (Marchenko et al, 1988), and induce intracellular calcium flux (Casto et al, 1992;Morii & Makinose, 1992). We have shown that binding of A p d to mouse brain synaptosomes is saturable and highly specific.…”

The Diadenosine Hexaphosphate Hydrolases fromSchizosaccharomyces pombe and Saccharomyces cerevisiae Are Homologues of the Human Diphosphoinositol Polyphosphate Phosphohydrolase

“…In higher eukaryotes, Ap n A appear also to be intracellular mediators of certain extracellular stimuli; they respond to glucose in pancreatic ␤-cells (10). Ap n A may also regulate ATP-sensitive K ϩ channels in ␤-cells and cardiac muscle (11)(12)(13) and intracellular ryanodine-binding Ca 2ϩ -release channels in cardiac and skeletal muscle, and in the brain (14,15). Finally, extracellular Ap 5 A and Ap 6 A have also been identified as neurotransmitters (2) and vasomodulators (16,17).…”