No abstract

2′‐& 3′‐O‐(4‐benzoylbenzoyl)‐ATP (BzATP) is the prototypic agonist for P2X7 receptors. In this study we demonstrate that bovine serum albumin (BSA) can affect the potency of BzATP at P2X receptors. BzATP potency (pEC50) to stimulate ethidium accumulation in cells expressing recombinant P2X7 receptors varied between 6.5 and 4, depending upon the species orthologue studied and ionic conditions employed. BSA (0.1 – 1 mg ml−1) and foetal bovine serum (FBS, 1 – 10% v v−1) inhibited responses to BzATP but only when the BzATP pEC50 exceeded 5. BSA did not block ATP‐stimulated ethidium accumulation, suggesting its effects were independent of P2X7 receptor blockade. BSA did not cause breakdown of nucleotides, although FBS (10% v v−1) exhibited appreciable nucleotidase activity and caused significant breakdown of ATP. In the presence of BSA, lipids such as 11‐((5‐dimethylaminonaphthalene‐1‐sulphonyl)amino)undecanoic acid (DAUDA) and arachidonic acid (AA) markedly increased BzATP potency. Lipids had no affect on ATP potency in the presence of BSA and had little effect on responses to BzATP in the absence of BSA. These results suggested that the reduction in BzATP potency by BSA was due to BzATP binding to BSA and that lipids prevented this binding. Consistent with this hypothesis, BzATP inhibited binding of the fluorescent lipid, DAUDA, to BSA. In conclusion, BSA and lipids can markedly affect BzATP potency at P2X7 receptors but this is probably a consequence of BzATP binding to BSA. This finding has important implications when using BzATP in vivo or in the presence of albumin. British Journal of Pharmacology (2001) 132, 1501–1508; doi:

Population studies on the detrital heavy minerals (64-250 um, specific gravity >2.92) of the Trias in the North Sea Basin demonstrate that there are well-defined regional and stratigraphical variations which are of use in correlation and palaeogeographic reconstruction. Two provinces are recognized: a region comprising the Southern North Sea, onshore England and the English Channel; and a Central North Sea Area.The heavy mineral assemblages of the Triassic sandstones of the Southern North Sea, onshore England and the English Channel are dominated by tourmaline. Wide-ranging correlation between the Southern North Sea and the English Channel has been achieved by using an horizon at which the heavy mineral assemblage is particularly rich in tourmaline. More detailed and local correlation is possible onshore, where rapid changes in the abundance of garnet, zircon, sphene and staurolite indicate the presence of local sources supplying sand detritus to the Trias.The Triassic sands of the Central North Sea are characterized by heavy mineral assemblages dominated by zircon, garnet or apatite. The zircon-rich assemblage is associated with the Smith Bank Formation and is interpreted as having been derived from the reworking of the Permian Sandstones to the west. The apatite-rich assemblage is linked to the Skagerrak and Marnock formations and was probably derived from an eastern Scandinavian source. The garnet-rich assemblage is of more limited extent and is restricted to sediments of Early Triassic age: its origin could have been the metamorphic terrain exposed in the region of the Halibut Horst.Preliminary studies on the chemistry of apatite (%F), tourmaline (%Ti0 2 ) and garnet (%CaO) grains from selected samples suggest that there is useful variation for the purposes of regional stratigraphy.

In this study we have expressed recombinant P2X7 receptors in HEK293 cells and examined the reasons for the species- and agonist-dependent differences in the time taken for the closure of the P2X7 receptor ion-channels after agonist removal. Channel closure times, measured in electrophysiological studies or by measuring cellular permeability to ethidium cations, were slower at rat than at human or mouse P2X7 channels following washout of the P2X7 agonist 2'- and 3'-O-(4-benzoylbenzoyl)-ATP (BzATP). In contrast, there were no species differences in channel closure times when ATP was the agonist. BzATP was more potent than ATP at the three species homologues and exhibited highest potency for rat P2X7 receptors suggesting that channel closure time was related to agonist potency. Furthermore, BzATP potency for the P2X7 receptor could be modified by changing extracellular ionic concentrations or by mutating the receptor and modifications which increased agonist potency also increased the time taken for channel closure. The dependence of channel closure time on agonist potency suggests it reflects agonist dissociation from the P2X7 receptor rather being an intrinsic property of the ion-channel. Consistent with this, our previous studies have shown that agonist potency increases after repeated agonist applications and in this study channel closure time at rat P2X7 receptors increased after repeated agonist applications. Overall these results suggest that the species differences in channel closure times reflect differences in agonist dissociation rates which arise as a consequence of the marked species differences in agonist potency.