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Differential sensitivity (DS) storage dynamics describe a temporal niche axis that determines coexistence of competing taxa through a trade-off between environmental insensitivity and competitive ability at the recruitment stage. In DS storage dynamics, when the relevant environmental factor is low, the more sensitive, better competitor preferentially recruits; when the environmental factor is high, the environmentally sensitive species suffers high mortality and the environmentally insensitive taxon preferentially recruits. A herbivore defense/growth rate trade-off at the seedling/juvenile stage could support this dynamic, We therefore compared juvenile palatability, a measure of anti-herbivore defense, and early growth rate for five congeneric pairs of native British herbs. All five comparisons showed a positive association between average individual growth rate and average palatability to a native slug species. We observed no evidence of associations between early growth rate and adult palatability or between early growth rate and life history strategy [annual vs. perennial). Seed mass was not associated with either early growth rate or with life history strategy whether or not relatedness was taken into account. We offer two explanations as to why we found statistically significant support for a growth rate defense trade-off when within-species studies so often produce only equivocal results. Key words: differential sensitivity storage dynamics: growth--defense trade-off herbivory; juvenile palatability; slugs: species coexistence.

Depletion of endoplasmic reticulum [Ca.sup.2+] stores leads to the entry of extracellular [Ca.sup.2+] into the cytoplasm, a process termed capacitative or store-operated [Ca.sup.2+] entry. Partially purified extracts were prepared from the human Jurkat T lymphocyte cell line and yeast in which [Ca.sup.2+] stores were depleted by chemical and genetic means, respectively. After microinjection into Xenopus laevis oocytes, the extracts elicited a wave of increased cytoplasmic free [Ca.sup.2+] ([[[Ca.sup.2+]].sub.i]) that spread from the point of injection across the oocyte. Extracts from cells with replete organellar [Ca.sup.2+] stores were inactive. The increases depended on extracellular [Ca.sup.2+], were unaffected by the inositol 1,4,5-trisphosphate (I[P.sub.3]) inhibitor heparin or an anti-I[P.sub.3] receptor antibody and were unchanged when the endoplasmic reticulum was segregated to the hemisphere opposite the injection site by centrifugation. Confocal microscopy revealed that [[[Ca.sup.2+]].sub.i] increases were most pronounced at the periphery of the oocyte. The patterns of [[[Ca.sup.2+]].sub.i] increases were replicated by computer simulations based on a diffusible messenger of about 700 Da that directly activates [Ca.sup.2+] influx. In addition, [I.sub.CRAC], a [Ca.sup.2+] release-activated [Ca.sup.2+] current monitored in Jurkat cells by whole-cell patch clamp recordings, was more rapidly activated when active extracts were included in the patch pipette than by the inclusion of a [Ca.sup.2+] chelator or I[P.sub.3]. These data support the existence in yeast and mammalian cells depleted of [Ca.sup.2+] stores of a functionally conserved diffusible calcium influx factor that directly activates [Ca.sup.2+] influx.

While regulation of receptor function is known to occur at many levels (e.g. transcriptional, post-translational), it is generally perceived that a tissue either expresses or does not express a particular receptor in an all-ornone fashion. Many pathological (e.g. tissue injury) and physiological (e.g. angiogenesis) processes have, however, been shown to be associated with the transcriptional induction of specific receptors. Induced receptors are not confined to any particular class, but range from G protein-coupled receptors to receptor tyrosine kinases. The potential implications of de novo receptor expression are profound with respect to potential novel therapeutic targets in specific disease states. Further, this observation may explain unexpected side-effects in the pharmacotherapy of existing disease states. In this article Lucy Donaldson, Michael Hanley and Amparo Villablanca discuss circumstances under which de novo receptor induction has been described, potential mechanisms of induction and the implications for pharmacology.

The experimental study and manipulation of programmed cell death has been greatly assisted by the identification of genetic and pharmacological tools that can either induce or block cell lethality. This review discusses new insights into the molecular sensing of perturbations induced by such tools, as well as the possible consequences of this detection in determining cell survival.

Xanthine oxidase (XO) is an endothelial enzyme which plays a role in producing toxic oxygen metabolites in acute reperfusion injuries. The effects of prolonged hypoxia on XO and xanthine dehydrogenase (XD) activities in endothelial cells were studied. The results showed that prolonged hypoxia increased the levels of both XO and XD in cultured endothelial cells. Furthermore, these increases contributed to oxygen radical-mediated injury as well as neutrophil adherence to endothelial cells. The results suggest that hypoxia injures endothelial cells by increasing XO and XD activities, which predispose these cells to oxidative and inflammatory attack.

Extracellular plaques made up of the peptide beta-amyloid found in the brains of people with Alzheimer's disease may be related to the disease symptomatically rather than causally. Ikuo Nishimoto and colleagues suggest that beta-amyloid precursor protein (APP), which gives rise to beta-amyloid, may also cause the plaques to form by controlling the heterotrimeric GTP-binding protein, G-O. However, APP's effect on other G proteins must be more fully assessed before this hypothesis can be accepted.

The long-sought molecular cloning of the human V2 vasopressin receptor has been achieved by two research groups. Vasopressin is a peptide hormone that acts on mammalian tissues and may affect G protein-coupled receptors in many ways, with the regulation of water retention by the kidneys being the most commonly known. The genetic sequence of V2 vasopressin receptors has a striking resemblance to the V1 vasopressin and oxytocin receptors, a result that may lead to further research on receptor structure and physiological function.