A potential fusion peptide and an integrin ligand domain in a protein active in sperm-egg fusion.

The union of sperm and egg is a special membrane fusion event that gives a signal to begin development. We have hypothesized that proteins mediating cell-cell fusion events resemble viral fusion proteins and have shown that PH-30, a sperm surface protein involved in sperm-egg fusion, shares biochemical characteristics with viral fusion proteins. We report here the complementary DNA and deduced amino-acid sequences of the mature alpha and beta subunits of PH-30. Both are type-I integral membrane glycoproteins. The alpha subunit contains a putative fusion peptide typical of viral fusion proteins and the beta subunit contains a domain related to a family of soluble integrin ligands found in snake venoms. Thus, the PH-30 alpha/beta complex resembles many viral fusion proteins in both its membrane topology and its predicted binding and fusion functions.     

Significant decadal-scale impact of volcanic eruptions on sea level and ocean heat content

Ocean thermal expansion contributes significantly to sea-level variability and rise. However, observed decadal variability in ocean heat content and sea level has not been reproduced well in climate models. Aerosols injected into the stratosphere during volcanic eruptions scatter incoming solar radiation, and cause a rapid cooling of the atmosphere and a reduction in rainfall, as well as other changes in the climate system. Here we use observations of ocean heat content and a set of climate simulations to show that large volcanic eruptions result in rapid reductions in ocean heat content and global mean sea level. For the Mt Pinatubo eruption, we estimate a reduction in ocean heat content of about 3 x 10(22) J and a global sea-level fall of about 5 mm. Over the three years following such an eruption, we estimate a decrease in evaporation of up to 0.1 mm d(-1), comparable to observed changes in mean land precipitation. The recovery of sea level following the Mt Pinatubo eruption in 1991 explains about half of the difference between the long-term rate of sea-level rise of 1.8 mm yr(-1) (for 1950-2000), and the higher rate estimated for the more recent period where satellite altimeter data are available (1993-2000).     

Isotopic evidence for Late Cretaceous plume-ridge interaction at the Hawaiian hotspot

When a mantle plume interacts with a mid-ocean ridge, both are noticeably affected. The mid-ocean ridge can display anomalously shallow bathymetry, excess volcanism, thickened crust, asymmetric sea-floor spreading and a plume component in the composition of the ridge basalts. The hotspot-related volcanism can be drawn closer to the ridge, and its geochemical composition can also be affected. Here we present Sr-Nd-Pb isotopic analyses of samples from the next-to-oldest seamount in the Hawaiian hotspot track, the Detroit seamount at 51 degrees N, which show that, 81 Myr ago, the Hawaiian hotspot produced volcanism with an isotopic signature indistinguishable from mid-ocean ridge basalt. This composition is unprecedented in the known volcanism from the Hawaiian hotspot, but is consistent with the interpretation from plate reconstructions that the hotspot was located close to a mid-ocean ridge about 80 Myr ago. As the rising mantle plume encountered the hot, low-viscosity asthenosphere and hot, thin lithosphere near the spreading centre, it appears to have entrained enough of the isotopically depleted upper mantle to overwhelm the chemical characteristics of the plume itself. The Hawaiian hotspot thus joins the growing list of hotspots that have interacted with a rift early in their history.     

Peripheral vascular effects of histamine administered into the cerebral ventricles of anaesthetized cats

Zusammenfassung An narkotisierten Katzen wurden der arterielle Blutdruck und der venöse Ausfluss aus der Vorderpfote oder aus dem Hinterbein registriert. Injektionen von Histamin in die Hirnventrikel bewirkten Erhöhung des Blutdruckes und Vasokonstriktion in der Vorderpfote. Im Hinterbein war die Vasokonstriktion weniger ausgesprochen. Auch nach Entfernung der Nebennieren war der Pressoreffekt vorhanden, woraus folgt, dass die periphere Vasokonstriktion für den durch intraventrikuläres Histamin hervorgerufenen Pressoreffekt verantwortlich ist.

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This work was supported by the Swedish Medical Research Council (Project No. W 349). Rheomacrodex was kindly supplied by Pharmacia, Uppsala (Sweden).