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.

/pdf/image-processing-with-imagej-2nw6tuidbb.pdf

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

/pdf/the-capsaicin-receptor-a-heat-activated-ion-channel-in-the-57mhjl9hkd.pdf

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.

[16] – Analysis of Calcium Fertilization Transients in Mouse Oocytes

Signalling pathways are composed of the ON mechanisms that generate internal signals and the OFF mechanism that remove these signals as cells recover from stimulation. Most attention will be focused on how second messengers and their downstream effectors are inactivated. The second messengers cyclic AMP and cyclic GMP are inactivated by phosphodiesterase (PDE). Inositol trisphosphate (InsP3) metabolism is carried out by both inositol trisphosphatase and inositol phosphatases. Diacylglycerol (DAG) metabolism occurs through two enzyme systems, DAG kinase and DAG lipase. In the case of Ca2+ signalling, recovery is carried out by the Ca2+ pumps and exchangers that remove Ca2+ from the cytoplasm. The mitochondria also play an important role in Ca2+ homoeostasis. Many of these second messengers activate downstream effectors through protein phosphorylation, and these activation events are reversed by corresponding protein phosphatases.

http://csb.portlandpresspublishing.com/content/ppcellsigbio/6/csb0001005.full.pdf

Module 5: OFF Mechanisms

Many hormones and neurotransmitters act by first binding to surface receptors which then transmit the information to various transducing elements responsible for generating intracellular signals such as cyclic AMP or calcium. These two second messengers seem to be associated with the action of a wide range of agonists. The generation of these messengers is mediated through two different types of receptor. The adrenergic system is a good example in that noradrenaline can act through β-receptors to generate cyclic AMP or through an α-receptor to produce a calcium signal. The existence of separate receptors associated with either cyclic AMP or calcium has now been recognised for other agonists such as histamine, 5-hydroxytryptamine, dopamine and even for peptide hormones such as vasopressin (Michell, 1979; Berridge, 1980a). There is considerable interest in the nature of the transducing mechanisms responsible for generating these second messengers. In the case of those receptors which function through cyclic AMP, a detailed biochemical description of how the receptor subunit may be coupled to adenylate cyclase is now available (Rodbell, 1980). Our understanding of how agonists activate adenylate cyclase has advanced to such an extent that it soon will be possible to reconstitute this transducing system fully. Of particular significance was the discovery that GTP-regulating proteins played a central role in the process of transducing information across the membrane (see Rodbell, 1980).

Phosphatidylinositol metabolism and calcium gating in a 5-HT receptor system

The arrival of a chemical signal at the surface of a cell initiates a profound change in cellular activity providing it can gain access to one of the intracellular signal pathways. These signal pathways begin at the cell surface with a specific receptor, which detects the external signal and relays the information to a limited number of transducing mechanisms, which encode the message into various second messengers. A classic example of an intracellular second messenger is cAMP. Recently there has been rapid progress in the identification of two new second messengers, inositol trisphosphate and diacylglycerol, which are related to each other in that they are both derived from a common precursor, which is a unique inositol lipid located within the inner leaflet of the plasma membrane (Berridge, 1984; Berridge and Irvine, 1984; Nishizuka, 1984a,b).

Agonist-Dependent Phosphoinositide Metabolism

Recently, attempts have been made to harmonize and simplify the nomenclature and abbreviations for inositol derivatives of biological importance, chiefly lipids and a variety of isomeric phosphates. The simplest suggestion was made by participants at the 1984 Chilton Conference (Agranoff et al. 1984). They proposed reducing the relatively cumbersome IUB/IUPAC-recommended abbreviations (e.g. PtdIns(4,5)P2 for phosphatidylinositol 4,5- bisphosphate, and Ins(1,4,5) P3for inositol 1,4,5-trisphosphate) to much simpler and easily spoken alternatives (PIP2 and IP3 for the above compounds). This proposal was simple and attractive at the time, but it was immediately rendered obsolete by the discovery of inositol 1,3,4-trisphosphate, which would have had to share a Chilton abbreviation with inositol 1,4,5- trisphosphate from which it is derived. To add to this potential confusion, we now have to contend with a minimum of three inositol tetrakisphosphate isomers. Following this meeting, we must also have distinct abbreviations for phosphatidylinositol 3-phosphate and phosphatidylinositol 4-phosphate: they cannot share PIP. ‘Modified Chilton’ systems that retain the brevity implicit in using an initial P to represent ‘phosphatidyl’ and I to represent ‘inositol’ have since been used in some publications (e.g. PI(4,5)P2 for phosphatidylinositol 4,5- bisphosphate, and I(1,4,5)P3 or (1,4,5)IP3 for inositol 1,4,5-trisphosphate). However, these are cumbersome to speak and have important disadvantages. ‘ I ’ is the accepted abbreviation for inosine, which also forms phosphate derivatives that have their own abbreviations (e.g. ITP), and bad typing often confuses I with 1; and, at least for the lipids, a capital P has two meanings within a single abbreviation, namely phosphatidyl (which should be a roman capital P) and phosphate (which should be italic).

Michael J. Berridge

Papers

[16] – Analysis of Calcium Fertilization Transients in Mouse Oocytes

Module 5: OFF Mechanisms

Phosphatidylinositol metabolism and calcium gating in a 5-HT receptor system

Agonist-Dependent Phosphoinositide Metabolism

A Comment on Nomenclature and Abbreviations