Ca2+]i in single isolated cardiac cells: a review of recent results obtained with digital imaging microscopy and fura-2

The use of fluorescent Ca2+ indicators to observe [Ca2+]i transients in voltage-clamped single cells has many advantages over previous methods, such as the use of aequorin in multicellular preparations, for studying excitation-contraction coupling. In the studies reviewed in this article, [Ca2+]i in single isolated mammalian ventricular myocytes was observed through the use of the fluorescent Ca2+ indicator, fura-2. Individual cells, loaded with fura-2 either by internal perfusion or by exposure to fura-2/AM, were generally studied with the use of inverted microscopes equipped with ultraviolet epifluorescence illumination, intensified silicon intensifier target cameras (ISIT), and (or) a photomultiplier tube. Analysis of subcellular patterns of fura-2 fluorescence was performed by digital analysis of the images obtained with the ISIT camera. Variation of membrane voltage and exposure of cells to ryanodine (which was assumed to selectively block the release of Ca2+ from the sarcoplasmic reticulum) were used to investigate the cellular processes that determine the [Ca2+]i transient. The main results of these studies are the following. (1) In any population of enzymatically isolated heart cells, there are (i) mechanically quiescent cells in which [Ca2+]i is spatially uniform, constant over time, and relatively low; (ii) spontaneously contracting cells, which have a relatively elevated [Ca2+]i, but in which the spatial uniformity of [Ca2+]i is interrupted periodically by spontaneous, propagating waves of high [Ca2+]i; and (iii) cells that are hypercontracted (rounded up) and that have higher levels of [Ca2+]i than the other two types.(ABSTRACT TRUNCATED AT 250 WORDS)     

Asymmetries in the Machband phenomena

The Mach bands are directly related to the size and the shape of on-center off-surround neural units in human vision. The effects of various stimulus parameters were studied on both bright and dark bands of equal plateau intensities. At low overall intensities, the dark band increases markedly in width, while the bright band does not. However, the bandwidth is more affected by the brightness slope, than by the plateau intensity per se. In this case, both bands vary approximately linearly and inversely with the log of the slope. The bright bands are slightly wider (4′) than the dark bands, for matched intensities. Both bands almost double in width with only a ±30′ para-foveal fixation. Optical blur enlarges the bands as predicted from the spread function. A comparable enlarging effect found with pupil size increase is not so readily understood. The apparent centers of the bright bands are positioned significantly more asymmetrically between the two edges than are the dark band centers. Eccentric neural units are considered as possible explanations for some of these non-linearities. Supported, in part, by Research Grant No. EY00319-05 from the National Eye Institute, National Institutes of Health, Bethesda, Maryland, and by a fight for Sight Grant-in-Aid G-428 from the National Council to Combat Blindness, Inc., New York, New York.     

Polypeptide changes associated with loss of proliferative potential during the terminal event in differentiation

The differentiation of murine mesenchymal stem cells occurs in nonterminal and terminal phases. In previous reports we established the characteristics of nonterminally differentiated cells and showed that transition from the nonterminal to the terminal state of differentiation can be induced by human plasma. We also showed that this transition is blocked by protein synthesis inhibitors and other pharmacological agents. In this paper, we have employed two-dimensional gel electrophoresis to evaluate changes in specific polypeptides that are induced when cells lose proliferative capacity associated with the terminal event in differentiation. Using silver staining procedures for analysis of electrophoretograms, we detected only seven major polypeptide differences between nonterminally differentiated and terminally differentiated cells. Six polypeptides were expressed only in preparations of terminally differentiated cells; these included two polypeptides identified in cytosolic fractions and four polypeptides identified in nuclear fractions. One polypeptide was also found to be selectively expressed only in nuclear fractions of nonterminally differentiated cells. Based on these observations we conclude that the loss of proliferative potential that occurs during the terminal event in mesenchymal stem cell differentiation is associated with changes in the composition of a limited number of specific polypeptides. We suggest that one or more of these polypeptides may be important in the regulation of cellular proliferation.     

Quantifying the extent of niche areas in the global fleet of commercial ships: the potential for “super-hot spots” of biofouling

Niche areas of ships, such as lateral thruster tunnels, sea chests, and propellers, are often hot spots for the accumulation of biofouling organisms, a potential source of aquatic invasive species. Yet, the relative importance of different niche areas is poorly resolved, in terms of both total surface area and the associated biota (i.e., the species of organisms and their abundances). To address this information gap, a method was developed to estimate the extent of various niche areas in the global fleet of 120,252 commercial ships active between 1999 and 2013. The total niche area for these vessels was estimated to be 32,996 × 10³ m², representing approximately 10% of the total wetted surface area (WSA) available for colonization by biota. Considering the portion of niche areas relative to the total WSA, it was highest for passenger vessels (27%), followed by tugs (25%), and fishing vessels (21%), with niche areas representing a small portion of the WSA for bulk carriers and tankers (7–8%). Examining the different types of niche areas, thruster tunnels had the greatest total extent (10,189 × 10³ m²), representing a disproportionately large contribution (>50%) of the total niche area for passenger vessels and tugs compared to other vessel types. This result, combined with the use and cleaning of thrusters, may render them “super-hot spots” of biofouling. The uneven distribution and extent of niche areas across vessels has implications for transfers of organisms and management strategies to reduce invasions associated with the surfaces of ships.