Wayne Rasband of NIH has created ImageJ, an open source Java-written program that is now at version 1.31 and is used for many imaging applications, including those that that span the gamut from skin analysis to neuroscience. ImageJ is in the public domain and runs on any operating system (OS). ImageJ is easy to use and can do many imaging manipulations. A very large and knowledgeable group makes up the user community for ImageJ. Topics covered are imaging abilities; cross platform; image formats support as of June 2004; extensions, including macros and plug-ins; and imaging library. NIH reports tens of thousands of downloads at a rate of about 24,000 per month currently. ImageJ can read most of the widely used and significant formats used in biomedical images. Manipulations supported are read/write of image files and operations on separate pixels, image regions, entire images, and volumes (stacks in ImageJ). Basic operations supported include convolution, edge detection, Fourier transform, histogram and particle analyses, editing and color manipulation, and more advanced operations, as well as visualization. For assistance in using ImageJ, users e-mail each other, and the user base is highly knowledgeable and will answer requests on the mailing list. A thorough manual with many examples and illustrations has been written by Tony Collins of the Wright Cell Imaging Facility at Toronto Western Research Institute and is available, along with other listed resources, via the Web.

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Image processing with ImageJ

Capsaicin, the main pungent ingredient in 'hot' chilli peppers, elicits a sensation of burning pain by selectively activating sensory neurons that convey information about noxious stimuli to the central nervous system We have used an expression cloning strategy based on calcium influx to isolate a functional cDNA encoding a capsaicin receptor from sensory neurons This receptor is a non-selective cation channel that is structurally related to members of the TRP family of ion channels The cloned capsaicin receptor is also activated by increases in temperature in the noxious range, suggesting that it functions as a transducer of painful thermal stimuli in vivo

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The capsaicin receptor: a heat-activated ion channel in the pain pathway

Protein kinase C has a crucial role in signal transduction for a variety of biologically active substances which activate cellular functions and proliferation. When cells are stimulated, protein kinase C is transiently activated by diacylglycerol which is produced in the membrane during the signal-induced turnover of inositol phospholipids. Tumour-promoting phorbol esters, when intercalated into the cell membrane, may substitute for diacylglycerol and permanently activate protein kinase C. The enzyme probably serves as a receptor for the tumour promoters. Further exploration of the roles of this enzyme may provide clues for understanding the mechanism of cell growth and differentiation.

The role of protein kinase C in cell surface signal transduction and tumour promotion

Inositol trisphosphate is a second messenger that controls many cellular processes by generating internal calcium signals. It operates through receptors whose molecular and physiological properties closely resemble the calcium-mobilizing ryanodine receptors of muscle. This family of intracellular calcium channels displays the regenerative process of calcium-induced calcium release responsible for the complex spatiotemporal patterns of calcium waves and oscillations. Such a dynamic signalling pathway controls many cellular processes, including fertilization, cell growth, transformation, secretion, smooth muscle contraction, sensory perception and neuronal signalling.

Inositol trisphosphate and calcium signalling

There has recently been rapid progress in understanding receptors that generate intracellular signals from inositol lipids. One of these lipids, phosphatidylinositol 4,5-bisphosphate, is hydrolysed to diacylglycerol and inositol trisphosphate as part of a signal transduction mechanism for controlling a variety of cellular processes including secretion, metabolism, phototransduction and cell proliferation. Diacylglycerol operates within the plane of the membrane to activate protein kinase C, whereas inositol trisphosphate is released into the cytoplasm to function as a second messenger for mobilizing intracellular calcium.

Inositol trisphosphate, a novel second messenger in cellular signal transduction.

I N T R O D U C T I O N An early event in evolution was the development of cell membranes, which served to encapsulate small microenvironments in which biochemical processes could occur with much greater efficiency. The presence of a hydrophobic barrier created problems with regard to gaining nutrients and eliminating waste products, which led to the development of numerous transport mechanisms to cope with this two-way traffic across the cell surface. In addition, this early cell had to be able to respond to changes in the environment and there probably was considerable selective advantage in developing receptor mechanisms for detecting external signals. The impermea­ bility of the surface membranes imposed serious difficulties in transmitting infor­ mation into the cell and this problem was solved in two quite separate ways. Certain chemicals, such as the steroid hormones, are hydrophobic and can pass through membranes en route to receptor sites within the nucleus. By far the majority of chemicals that influence cellular activity, however, are hydrophilic and must exert their effects without entering the cell. Their action depends on elegant transduction processes within the cell membrane, which detect external signals and transduce the information into a limited repertoire of internal signals (second messengers). This article deals with a newly discovered transduction mechanism, based on inositol lipids, which is responsible for controlling many aspects of cell function including, it seems, the crucial decision about whether or not to grow.

Cell signalling through phospholipid metabolism.

The primary function of inositol 1,4,5-trisphosphate (InsP3) is to function as a second messenger to release Ca2+ from internal stores. Many cell stimuli act on receptors that are coupled to phospholipase C that hydrolyses phosphatidylinosol 4,5-bisphosphate (PIP2) to release InsP3 to the cytosol. InsP3 receptors located on the endoplasmic reticulum respond to this elevation of InsP3 by releasing Ca2+, which is often organized into characteristic spatial (elementary events and waves) and temporal (Ca2+ oscillations) patterns. This InsP3/Ca2+ pathway has been adapted to control processes as diverse as fertilization, proliferation, contraction, cell metabolism, vesicle and fluid secretion, and information processing in neuronal cells.

Inositol Trisphosphate and Calcium Signaling

Signal-induced CA2+ oscillations : properties of a model based on Ca2+-induced CA2+ release

Hormone-evoked Elementary Ca2+ Signals Are Not Stereotypic, but Reflect Activation of Different Size Channel Clusters and Variable Recruitment of Channels within a Cluster

Exposure of freshly ovulated mouse oocytes to a fertilising spermatozoon, thimerosal, Sr2+ or acetylcholine induced similar Ca2+ spiking responses. We propose that each of the four agents reduces the threshold for Ca2+ release from internal stores, but by different mechanisms. All agents except thimerosal stimulated oocyte activation, but thimerosal caused dissassembly of the meiotic spindle and thus prevented progress into interphase. Dithiothreitol (DTT) completely blocked and reversed the spiking responses induced by thimerosal, but facilitated and accelerated those induced by spermatozoa, Sr2+ and acetylcholine. The stimulatory effect of DTT was not simply a consequence of progress into interphase, but was attributable, at least in part, to an enhancement of divalent cation entry, as measured by Mn2+ quench analysis of fura-2 in both fertilised and unfertilised oocytes. Possible mechanisms by which DTT might achieve its effects are discussed.

Michael J. Berridge

Papers

Cell signalling through phospholipid metabolism.

Inositol Trisphosphate and Calcium Signaling

Signal-induced CA2+ oscillations : properties of a model based on Ca2+-induced CA2+ release

Hormone-evoked Elementary Ca2+ Signals Are Not Stereotypic, but Reflect Activation of Different Size Channel Clusters and Variable Recruitment of Channels within a Cluster

Fertilisation and thimerosal stimulate similar calcium spiking patterns in mouse oocytes but by separate mechanisms