Effects of modulators of myosin light-chain kinase activity in single smooth muscle cells

Ca2+ imaging in single living cells: theoretical and practical issues

The measurement of intracellular calcium ion concentrations [( Ca2+]i) in single living cells using quantitative fluorescence microscopy draws from a diverse set of disciplines, including cellular biology, optical physics, statistics and computer science. Over the last few years, we have devised and built a number of systems for measuring [Ca2+]i with Fura-2, and have applied them in the exploration of a wide range of biological processes controlled by Ca2+. In this report we discuss these systems and their advantages and limitations. We also describe the theoretical and practical problems associated with using Fura-2 to measure [Ca2+]i, and the solutions that we, and others, have developed to overcome them. The approaches described should provide useful guidance for others interested in imaging [Ca2+] distribution in living cells. The factors that limit current methods are discussed, and areas for future development are highlighted.

Formation, transport, contraction, and disassembly of stress fibers in fibroblasts

Swiss mouse 3T3 fibroblasts grown on a solid substrate in the presence of 10% serum exhibit cell movement, organelle transport, and cytokinesis. When the serum concentration in the culture medium is decreased to 0.2% for 48 h the serum-deprived cells virtually stop locomoting, spread, decreased organelle transport, and exhibit extensive arrays of stress fibers that are visible with video-enhanced differential interference contrast microscopy and that also incorporate fluorescent analogs of actin and conventional myosin (myosin II). The stress fibers form in a constitutive manner at the cytoplasm-membrane interface, transport toward the nucleus, and then disappear. The rate of transport of these fibers is quite heterogeneous with average rates in the range of 10-20 microns/h. When serum-deprived cells are stimulated with mitogens such as 10% serum or 10 nM thrombin, many of the stress fibers immediately begin to shorten, suggesting a contraction. The rate of shortening is approximately two orders of magnitude slower than that of unloaded smooth muscle cells. The fiber shortening is often accompanied by retraction of the edges of the cell and continues for at least the 1st hour post-stimulation.