This article reviews the progress of atomic force microscopy in ultrahigh vacuum, starting with its invention and covering most of the recent developments. Today, dynamic force microscopy allows us to image surfaces of conductors and insulators in vacuum with atomic resolution. The most widely used technique for atomic-resolution force microscopy in vacuum is frequency-modulation atomic force microscopy (FM-AFM). This technique, as well as other dynamic methods, is explained in detail in this article. In the last few years many groups have expanded the empirical knowledge and deepened our theoretical understanding of frequency-modulation atomic force microscopy. Consequently spatial resolution and ease of use have been increased dramatically. Vacuum atomic force microscopy opens up new classes of experiments, ranging from imaging of insulators with true atomic resolution to the measurement of forces between individual atoms.

https://hep.physics.utoronto.ca/WilliamTrischuk/courses/phy189/AFM_revmodphys.pdf

Advances in atomic force microscopy

Identification and localization of synaptophysin, an integral membrane glycoprotein of Mr 38,000 characteristic of presynaptic vesicles.

This lecture summarizes the knowledge in a field dubbed autopharmacology: the secretion by a body cell of a substance prompted by an internal stimulus. The majority of the work reported on here was with the adrenal chromaffin cell. Topics covered describing and proving the release of secretion into the chromaffin cells extracellular environment are means of intracellular recording from chromaffin cells and the effect of acetylcholine on membrane potential and consequences of exposing the cell to acetylcholine (altered membrane chemistry increased membrane permeability entry of sodium and calcium ions and depolarization). Also postulated are 2 possible mechanisms of catecholamine secretion (both involve release directly from chromaffin granules to the cell exterior through frank rupture of the adherent membranes of granule and cell i.e. exocytosis or through some greatly increased permeability at the adhesion site). The lecture then focuses on calcium and stumulus secretion coupling in other systems including the exocrine glands neurones and neurosecretory cells the mast cell and polymorphonuclear leukocytes. In a concluding discussion on the role of calcium in secretory mechanisms the presence of prostaglandin in effluent from adrenal glands exposed to acetylcholine is mentioned as evidence of the secretory mechanism being a chemical reaction.

Stimulus-secretion coupling: the concept and clues from chromaffin and other cells.

The precursor protein of non-Aβ component of Alzheimer's disease amyloid is a presynaptic protein of the central nervous system

Extracellular ATP, at micromolar concentrations, induces significant functional changes in a wide variety of cells and tissues. ATP can be released from the cytosol of damaged cells or from exocytotic vesicles and/or granules contained in many types of secretory cells. There are also efficient extracellular mechanisms for the rapid metabolism of released nucleotides by ecto-ATPases and 5'-nucleotidases. The diverse biological responses to ATP are mediated by a variety of cell surface receptors that are activated when ATP or other nucleotides are bound. The functionally identified nucleotide or P2-purinergic receptors include 1) ATP receptors that stimulate G protein-coupled effector enzymes and signaling cascades, including inositol phospholipid hydrolysis and the mobilization of intracellular Ca2+ stores; 2) ATP receptors that directly activate ligand-gated cation channels in the plasma membranes of many excitable cell types; 3) ATP receptors that, via the rapid induction of surface membrane channels and/or pores permeable to ions and endogenous metabolites, produce cytotoxic or activation responses in macrophages and other immune effector cells; and 4) ADP receptors that trigger rapid ion fluxes and aggregation responses in platelets. Current research in this area is directed toward the identification and structural characterization of these receptors by biochemical and molecular biological approaches.

https://www.physiology.org/doi/pdf/10.1152/ajpcell.1993.265.3.C577

Signal transduction via P2-purinergic receptors for extracellular ATP and other nucleotides

The chromogranins A and B: The first 25 years and future perspectives

Th molecular organization of adrenal chromaffin granules

The composition of adrenal chromaffin granules: An assessment of controversial results

The molecular function of adrenal chromaffin granules: Established facts and unresolved topics

1. A soluble protein has been purified from an aqueous extract of bovine adrenal chromaffin granules by chromatography on Sephadex G-200. This protein comprises 25% of the total protein of the granules and gave a single band on gel electrophoresis. 2. The protein is unusually rich in acidic amino acids, notably glutamic acid (26·0%, w/w); it is also relatively rich in proline (8·6%, w/w) but poor in cystine (0·35%, w/w). 3. A molecular weight of 77000 was obtained from sedimentation and diffusion measurements on the protein, and approach-to-equilibrium measurements gave apparent molecular weights of the same order. 4. A molecular weight 7 times that given above was estimated from the results of chromatography on a column of Sephadex G-200 that had been calibrated with globular proteins. However, good agreement between the ultracentrifuge and Sephadex experiments was obtained on the assumption that Sephadex chromatography depends on the effective hydrodynamic radii of proteins and not on their molecular weights. 5. The hydrodynamic properties of the protein differed from those of a typical globular protein. Thus the protein had a high intrinsic viscosity, a high frictional ratio and a large effective hydrodynamic volume. 6. The hydrodynamic properties of the protein, but not its molecular weight, were dependent on the ionic strength of the solvent. Increasing the ionic strength caused an increase in the sedimentation and diffusion coefficients, but a decrease in the intrinsic viscosity and in the frictional ratio of the protein. 7. Optical-rotatory-dispersion measurements indicated that only a small part of the polypeptide chain was in an α-helical conformation. 8. These results are compatible with the protein's having a conformation approaching that of a random-coil polypeptide, the volume occupied by the molecule being determined by electrostatic repulsion between the excess of negative charges.

Hans Winkler

Papers

The chromogranins A and B: The first 25 years and future perspectives

Th molecular organization of adrenal chromaffin granules

The composition of adrenal chromaffin granules: An assessment of controversial results

The molecular function of adrenal chromaffin granules: Established facts and unresolved topics

Purification and properties of an acidic protein from chromaffin granules of bovine adrenal medulla.