Regulated secretion occurs when the ceil detects a signal, vesicles containing the secretory product fuse with the plasma membrane of the cell, and the contents are released into the extracellular space. This mechanism is called exocytosis. Many laboratories around the world have studied exocytosis for the past couple of decades, and we know a lot about the many steps that are involved. The cytoskeleton appears to play a role in allowing vesicles to approach the plasma membrane, and many other proteins are in the cascade between reception of the signal and the release of the secretory products.

The recordable compact disc (CDR) is a popular and inexpensive medium for storing and disseminating digital information, such as micrographs and scanned images. This technical note describes unusual degradation that rendered a group of discs unreadable. The discs were purchased as a set. Each disc was packaged in a jewel box and wrapped in clear plastic. Several of the discs were used within weeks of purchase to store data, which included digital micrographs.

Most objects in our world are 3-dimensionai (3-D), and this is certainly true of cellular ultrastructure. The challenge in microscopy has always been how to analyze this 3-D information. Traditional thin-section microscopy has a minimal ability to view 3-D structure, because it is limited to viewing thin, almost twodimensional (2-D) planes taken from the specimen. The development of high and intermediate voltage electron microscopes (HVEM and IVEM) provides the ability to investigate the ultrastructure of thick biological samples—allowing a unique view of the 3-D interrelationships of cells and organelles.

During the past decade there has been remarkable progress in understanding the behavior and function of biological cells. Progress was accelerated by the development of microscopic imaging techniques and fluorescent dyes that allowed investigators to visualize dynamic processes within subcellular compartments in heterogenous populations of living cells. These capabilities led to exciting new discoveries in cellular and molecular studies of a wide variety of cell types.

Efforts to study living cells under microscopic conditions are not without problems, however. The most vexing problem is phototoxicity caused by either illumination alone (endogenous toxicity) or illumination of fluorescent dyes loaded into cells (exogenous toxicity). In this report I provide an overview of these general types of toxicity as well as describe recent results that may shed light on how to reduce them.

It is crucial to get a thin glue line when making TEM cross section samples, so normally a clamp is used to press the samples together during curing. Several types of clamps are available commercially, however almost all of them have a big disadvantage: the pressure cannot be adjusted. Basically there are two types of clamps. Type 1 is a small vise that uses a screw to press the samples together. There are two problems associated with type 1. The first one is that usually the viscosity of the glue decreases during the initial stage of curing, so even if you had tightened the screw hard, the sample could still get loose because the glue becomes thinner as its viscosity reduces. To get a thin glue line with this type of clamp, one has to keep retightening trje screw when the clamp and sample is being heated.

For several months there have been recurring threads on microscopy-related internet listservers concerning health and safety issues that have troubled us greatly at Anatech Ltd. The general theme has been to make light of toxicity claims, provide anecdotal comments about having survived many decades of working in labs, and giving the impression that current health and safety regulations are at best a pain and probably are the cunning products of misguided governmental agencies.

The great hazard of formaldehyde is not its proven carcinogenicity. Anyone interested in formaldehyde's effects on humans should read the preamble to OSHA's Formaldehyde Standard (Federal Register 52(233):46168-46312; December 4, 1987). According to studies cited therein, formaldehyde has been directly implicated in causing tumors in the lungs, nasoand oro-pharynx and nasal passages of humans occupationally exposed to levels of formaldehyde not unlike conditions existing in histology laboratories a few decades ago. Repeated and prolonged exposure increases the risk.

This effect can be understood by considering what happens to the cantilever and tip as the base of the vibrating cantilever is brought closer to the sample (like in a force curve). When the vibrating cantilever first approaches the surface, the tip senses attractive forces. In standard imaging conditions, these are usually due to meniscus forces between a layer of adsorbed liquid (often water) on the surface of the sample and the tip. However, even in clean conditions, other attractive forces like Van der Waals will generally be present. These attractive forces move the resonance of the cantilever downward in frequency. Since the cantilever is being driven at the original resonance frequency of the cantilever, this will cause the cantilever amplitude to decrease as the attractive forces puli the resonance peak out from under the drive frequency. This decrease is often quite linear with distance, but doesn't have to be. In this case the tip is actually turning around some distance (this could typically be a few nanometers) before it touches the surface. This regime is commonly called the “attractive” regime because attractive forces dominate the behavior of the cantilever.