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The concentration of cytosolic free Ca2l ([Ca2+]J) and the release of tritiated norepinephrine ([3HJNE) were monitored during Ba2+ stimulation of sympathetic neurons cultured from chick embryos. Ba2+ (2.5 (17).Indo-1 Emission Spectra. Emission spectra of indo-1 were determined in the presence of increasing concentrations of Ca2+, Ba2+, and Ca2+ in the presence of Ba2+ by using a scanning spectrofluorometer (SPF-500C, SLM Aminco, Urbana, IL) with excitation at 355 nm and emission recorded from 360 to 550 nm (60 nm/min, slit width 4 nm). Solutions and calculations offree Ca2+ and Ba2+ were the same as those used for determining the standard curve of indo-1 emission ratios with the ACAS laser photometer (below).Indo-1 Imaging of [Ca2+];. Cultured sympathetic neurons were loaded with 0.25 ,uM indo-1 acetoxymethyl ester for monitoring [Ca2+]J (18) on an ACAS laser photometer (Meridian Instruments, Lansing, MI). Excitation was at 353-361 nm, and indo-1 fluorescence was recorded at 405 nm (Ca2+-bound) and 485 nm (Ca2+-free) for ratio determination (19). Simultaneous images at the two wavelengths were obtained over 10-sec periods at rest, coincident with electrical stimulation or following addition of Ba2+. To control for nonspecific charge effects, Ca2+-free Krebs solution was supplemented with an additional 2.5 mM MgCl2. In all experiments each cell body, neurite, or growth cone was used as its own control. A standard curve of indo-1 emission ratios (405 nm/485 nm) versus Ca2+ concentration (0-11.3 ,uM) and Ba2+ concentration (0-50.4 .uM) was determined in calibration buffer containing 100 mM KCI, 1 mM EGTA, 50 mM Hepes, and 1 ,uM indo-1 salt, pH 7.2 at 250C. 557The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

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A 57-year-old man presented with several hours of chest discomfort accompanied by ischemic changes on his electrocardiogram. He had undergone coronary-artery bypass grafting and subsequent percutaneous coronary intervention one year earlier, with deployment of a stent in the saphenous-vein graft to the first obtuse marginal artery. Cardiac angiography showed severe three-vessel disease of the native coronary arteries, a patent graft involving the left internal thoracic artery and the left anterior descending coronary artery, a previously identified occluded vein graft anastomosed to the right coronary artery, and a newly occluded vein graft anastomosed to the first obtuse marginal artery. The midportion of the stent was fractured. Multiple attempts to penetrate this occlusion with a wire were unsuccessful. The patient required an intraaortic balloon pump for the management of recurrent chest pain. Seven days later, he again underwent surgical revascularization.Review of the cineangiogram obtained during the first catheterization showed that the stent was suboptimally deployed, resulting in narrowing of the midportion. Fracture of the midportion was most likely due to shear forces resulting from cardiac contractions.

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