Gew?lle und Kleins?uger-Forschung

Ohne Zusammenfassung     

Effects of monovalent cations on red cell shape and size

Human erythrocytes were incubated in isotonic solutions of different monovalent cations. The apparent size of the red cells measured on scanning electron microscopic pictures decreases in the order Li+ greater than Na+ = K+ greater than Rb+. These differences in size are abolished after pretreatment with trypsin, which removes a large part of the charges associated with membrane glycoproteins. Shape alterations are also observed. Normal biconcave shapes are visible after Na+ or K+ incubation, whereas Li+ leads to flabby, flattened cells with a certain tendency to crenation, and Rb+ causes more pronounced biconcavity with a certain tendency to cupping. The overall effects of pretreatment with trypsin are similar to those of Li+. Our results provide evidence that the electrostatic repulsion of glycoproteins and other charged membrane components may play an essential role in maintaining red cell shape.     

Die praktische Belevanz des McNemar-Tests

By application of the McNemar-Test the question of the practical relevance (practical significance) of the resulting test statistic generally arises. An analogy to the t-Test for paired measurements gives some measure for the practical relevance. The evaluation of this relevance is based upon suggestions made by COHEN (1977).     

Human cardiac telocytes: 3D imaging by FIB‐SEM tomography

Telocyte (TC) is a newly identified type of cell in the cardiac interstitium ( www.telocytes.com ). TCs are described by classical transmission electron microscopy as cells with very thin and long telopodes (Tps; cellular prolongations) having podoms (dilations) and podomers (very thin segments). TCs' three‐dimensional (3D) morphology is still unknown. Cardiac TCs seem to be particularly involved in long and short distance intercellular signalling and, therefore, their 3D architecture is important for understanding their spatial connections. Using focused ion beam scanning electron microscopy (FIB‐SEM) we show, for the first time, the whole ultrastructural anatomy of cardiac TCs. 3D reconstruction of cardiac TCs by FIB‐SEM tomography confirms that they have long, narrow but flattened (ribbon‐like) telopodes, with humps generated by the podoms. FIB‐SEM tomography also confirms the network made by TCs in the cardiac interstitium through adherens junctions. This study provides the first FIB‐SEM tomography of a human cell type.     

Referate

Ohne Zusammenfassung     

Light-dependent repetitive Ca2+ spikes induced by extracellular application of neomycin in honeybee drone photoreceptors

Photoreceptor cells of the honeybee drone fire, in the presence of the polycationic aminoglycoside neomycin, repetitive slow spike-like potentials superimposed on the receptor potential plateau phase. We have used conventional intracellular recordings and microfluorometric intracellular Ca²⁺ measurements to characterize these spike potentials. We have shown that the spike frequency increases in a light-intensity-dependent manner. The spikes are fired only when light stimuli depolarize the cell from a resting potential of −50 to −60 mV to at least −40 to −45 mV; they are tetrodotoxin insensitive and blocked by the Ca²⁺ channel blockers Ni²⁺, Cd²⁺, ω-agatoxin TK, verapamil and methoxyverapamil. Depolarization of the photoreceptors with high extracellular K⁺ in the presence of neomycin in darkness does not generate spikes. Small intracellular Ca²⁺ oscillations superimposed on the plateau phase of the light-induced increase in intracellular free Ca²⁺ concentration have a similar temporal pattern as the spike-like potentials. We conclude that the spike-like potentials require stimulation by light and are generated by voltage-dependent Ca²⁺ channels localized on the soma of the photoreceptors, distal to the basal lamina. Accepted: 16 March 2000     

Actions of neomycin on electrical light responses, Ca2+ release, and intracellular Ca2+ changes in photoreceptors of the honeybee drone

Neomycin, known to inhibit phospholipase C-mediated IP3 formation, was applied in the bath or injected into cells and its effects on electrical light responses were analyzed. Neomycin effects on inositol 1,4,5-trisphosphate- and Ca2+-induced Ca2+ release from the endoplasmic reticulum and/or the light-induced Ca2+ elevation were also studied. Neomycin (0.5 mmol x l(-1)) blocked inositol 1,4,5-trisphosphate-, caffeine-, and Ca2+-induced Ca2+ release. Bath application of neomycin decreased the sensitivity to 20-ms light flashes by a factor of up to 100 and slowed the kinetics of dim flash responses. Intracellularly injected neomycin desensitized the photoreceptors more than 1 log unit, increased the latency, and slowed the rate of rise of the light response. Neomycin (0.5 mmol x l(-1)) in the bath delayed and reduced the transient component of responses to 1-s steps of light at intermediate intensities. It also decreased and slowed the light-induced, and it blocked the caffeine-induced intracellular Ca2+ elevation. The combined pharmacological effects of neomycin are suggested to decrease the Ca2+-mediated amplification of the phototransduction cascade and the Ca2+-mediated acceleration of processes determining the kinetics of light responses.