Microdomain Ca2+ Activation during Exocytosis in Paramecium Cells. Superposition of Local Subplasmalemmal Calcium Store Activation by Local Ca2+ Influx

In Paramecium tetraurelia, polyamine-triggered exocytosis is accompanied by the activation of Ca2+-activated currents across the cell membrane (Erxleben, C., and H. Plattner. 1994. J. Cell Biol. 127:935– 945). We now show by voltage clamp and extracellular recordings that the product of current × time (As) closely parallels the number of exocytotic events. We suggest that Ca2+ mobilization from subplasmalemmal storage compartments, covering almost the entire cell surface, is a key event. In fact, after local stimulation, Ca2+ imaging with high time resolution reveals rapid, transient, local signals even when extracellular Ca2+ is quenched to or below resting intracellular Ca2+ concentration ([Ca2+]e ⩽ [Ca2+]i). Under these conditions, quenched-flow/freeze-fracture analysis shows that membrane fusion is only partially inhibited. Increasing [Ca2+]e alone, i.e., without secretagogue, causes rapid, strong cortical increase of [Ca2+]i but no exocytosis. In various cells, the ratio of maximal vs. minimal currents registered during maximal stimulation or single exocytotic events, respectively, correlate nicely with the number of Ca stores available. Since no quantal current steps could be observed, this is again compatible with the combined occurrence of Ca2+ mobilization from stores (providing close to threshold Ca2+ levels) and Ca2+ influx from the medium (which per se does not cause exocytosis). This implies that only the combination of Ca2+ flushes, primarily from internal and secondarily from external sources, can produce a signal triggering rapid, local exocytotic responses, as requested for Paramecium defense

Reliability of NI-RADS criteria in the interpretation of contrast-enhanced magnetic resonance imaging considering the potential role of diffusion-weighted imaging

Objectives: To assess inter- and intrareader agreement of the Neck Imaging Reporting and Data System (NI-RADS) used in contrast-enhanced magnetic resonance imaging (MRI) including analysis of diffusion-weighted imaging (DWI), which is currently not part of the NI-RADS criteria. Methods: This retrospective study included anonymized surveillance contrast-enhanced MRI datasets of 104 patients treated for different head and neck cancers. Three radiologists experienced in head and neck imaging reported findings for the primary site and the neck using NI-RADS criteria in a first step and evaluated DWI sequences for the primary site in a second step. Thirty randomly selected imaging datasets were again presented to the readers. Kappa statistics and observed agreement (A(o)) were calculated. Results: Interreader agreement across all MRI datasets was moderate (kappa(Fleiss) = 0.53) for NI-RADS categories assigned to the primary site, substantial for NI-RADS categories of the neck (kappa(Fleiss) = 0.67), and almost perfect for DWI of the primary site (kappa(Fleiss) = 0.83). Interreader agreement for the primary site was particularly low in cases of cancer recurrence (kappa(Fleiss) = 0.35) and when categories 2a, 2b, and 3 were combined (kappa(Fleiss) = 0.30). Intrareader agreement was considerably lower for NI-RADS categories of the primary site (range A(o) = 53.3-70.0%) than for NI-RADS categories of the neck (range A(o) = 83.3-90.0%) and DWI of the primary site (range A(o) = 93.3-100.0%). Conclusion: Interreader agreement of NI-RADS for reporting contrast-enhanced MRI findings is acceptable for the neck but limited for the primary site. Here, DWI has the potential to serve as a reliable additional criterion

Ca 2� release from subplasmalemmal stores as a primary event during exocytosis in Paramecium cells

Abstract. A correlated electrophysiological and light microscopic evaluation of trichocyst exocytosis was carded out with Paramecium cells which possess extensive cortical Ca stores with footlike links to the plasmalemma. We used not only intra- but also extracellular recordings to account for polar arrangement of ion channels (while trichocysts can be released from all over the cell surface). With three widely different secretagogues, aminoethyldextran (AED), veratridine and caffeine, similar anterior Nain and posterior Kout currents (both known to be Ca 2+dependent) were observed. Direct de- or hyperpolarization induced by current injection failed to trigger exocytosis. For both, exocytotic membrane fusion and secretagogue-induced membrane currents, sensitivit

Anfangsgründe der Naturlehre

entworfen von Johann Christian Polykarp Erxleben ... mit Zusätzen von G. C. Lichtenberg ..

Anfangsgründe der Naturlehre

Entworfen von Johann Christian Polykarp Erxleben, weil. der Weltweisheit D. und Prof. auf der Georg Augusts-Universität ...Nicht identisch mit VD18 11395575, dort anderer Umfang: LIX, 755 S., [15] Bl., [1], VIII Faltbl., auch mit unterschiedl. ZeilenbrüchenAutopsie nach Ex. der ULB Sachsen-AnhaltVorlageform des Erscheinungsvermerks: Göttingen, bey Johann Christian Dietrich, 1791

Anfangsgründe der Naturlehre

entworfen von Johann Christian Polykarp Erxleben ... mit Zusätzen von G.C. Lichtenberg, königl. Grossbrit. Hofr. und Prof. zu Göttinge

Avctoritate Serenissimi Ac Potentissimi Principis Gvilielmi IX. Hassiae Landgravii Reliqva Rectoris Academiae Magnificentissimi Solemnia Novi Prorectoris Creandi Inavgvrandiqve Ad Ipsas Calendas Ianvarii A. MDCCLXXXIX. Indicit Prorector Academiae Iohannes Henricvs Christianvs Erxleben Ivr. Vtr. Doct. Profess. Pvbl. Ordinar. Et Sereniss. Hassiae Landgravio A Consil. Ivstit. Intimis.

Inest: Potestas Criminalis Circa Frequentiam Delictorum In Disceptationem VocataAutopsie nach Ex. der ULB Sachsen-AnhaltVorlageform des Erscheinungsvermerks: Marbvrgi Typis Iohannis Bayrhofferi