Secretagogue-induced Ca2+ oscillations in isolated canine gastric chief cells

Agonist-induced changes in cytoplasmic free Ca2+ concentration (|Ca2+|i) of isolated canine gastric chief cells were evaluated by microspectrofluorometry of superfused fura-2 loaded cells. Application of high concentrations of carbachol (CCh, 10-5 M) or cholecystokinin octapeptide (10-8 M) resulted in biphasic Ca2+ mobilization comprising an initial large transient followed by a small sustained evaluation above the prestimulation level. Submaximal concentrations of CCh (10-6 M) or cholecystokinin (10-9 M) led to either a transient series of large amplitude Ca2+ spike(s) or a higher frequency of sustained Ca2+ oscillations of smaller amplitude. Cholecystokinin at 10-10 M induced only sustained Ca2+ oscillations. Elimination of Ca2+ from the medium had no immediate effect on oscillations indicating an intracellular source of Ca2+. Thus the Ca2+ signalling mode in chief cells is dependent on agonist concentrations.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29492/1/0000578.pd

Change and Exchange: Economies of Literature and Knowledge in Early Modern Europe

The introductory essay outlines the way in which Change and Exchange places literature, and, in a wider sense, imaginative practice, at the centre of early modern economic knowledge. Probing the affinity between economic and metaphorical experience in terms of the transactional processes of change and exchange, it sets up the parameters within which the essays in the volume collectively forge a language to grasp early modern economic phenomena and their epistemic dimensions. It prepares the reader for the stimulating combination of materials that the book presents: the range of generic contexts engendered by emergent economic practices, structures of feeling and modes of knowing made available by new economic relations, and economies of transformation in discursive domains that are distinct from ‘economics’ as we understand it but cognate in their intuition of change and exchange as shaping agents

Phenotypic Variation and Bistable Switching in Bacteria

Microbial research generally focuses on clonal populations. However, bacterial cells with identical genotypes frequently display different phenotypes under identical conditions. This microbial cell individuality is receiving increasing attention in the literature because of its impact on cellular differentiation, survival under selective conditions, and the interaction of pathogens with their hosts. It is becoming clear that stochasticity in gene expression in conjunction with the architecture of the gene network that underlies the cellular processes can generate phenotypic variation. An important regulatory mechanism is the so-called positive feedback, in which a system reinforces its own response, for instance by stimulating the production of an activator. Bistability is an interesting and relevant phenomenon, in which two distinct subpopulations of cells showing discrete levels of gene expression coexist in a single culture. In this chapter, we address techniques and approaches used to establish phenotypic variation, and relate three well-characterized examples of bistability to the molecular mechanisms that govern these processes, with a focus on positive feedback.

Geography and the Paris Academy of Sciences: politics and patronage in early 18th-century France

This essay considers the politics and patronage of geography in early-modern France. It examines how the Paris Academy of Sciences, widely acknowledged as the 18th century’s pre-eminent scientific society, came to recognise geography as an independent science in 1730, a century before the establishment of the first geographical societies. Although the Academy was centrally concerned with cartography from its inception in 1666, it initially afforded no official status to geography, which was viewed either as a specialised form of historical inquiry or as a minor component within the hegemonic science of astronomy. The rise of Newtonian mathematics and the associated controversy about the shape of the earth challenged the Academy’s epistemological foundations and prompted a debate about the educational and political significance of geography as a scientific practice. The death in 1726 of Guillaume Delisle, a prominent Academy astronomer-cartographer and a popular geography tutor to the young Louis XV, led to a spirited campaign to elect Philippe Buache, Delisle’s prot�eg�e, to a new Academy position as a geographer rather than an astronomer. The campaign emphasised the social and political utility of geography, though the Academy’s decision to recognise this new and distinctively modern science was ultimately facilitated by traditional networks of patronage within the French Royal Court