Abstract-To investigate the cellular mechanisms for altered Ca 2ϩ homeostasis and contractility in cardiac hypertrophy, we measured whole-cell L-type Ca 2ϩ currents (I Ca,L ), whole-cell Ca 2ϩ transients ([Ca 2ϩ ] i ), and Ca 2ϩ sparks in ventricular cells from 6-month-old spontaneously hypertensive rats (SHRs) and from age-and sex-matched Wistar-Kyoto and Sprague-Dawley control rats. By echocardiography, SHR hearts had cardiac hypertrophy and enhanced contractility (increased fractional shortening) and no signs of heart failure. C ardiac hypertrophy is associated with marked changes in myocardial contractility. Peak active tension increases, 1-4 and the rates of both contraction and relaxation are slowed. 3,[5][6][7][8] These contractile abnormalities are associated with alterations in the whole-cell calcium transient ([Ca 2ϩ ] i ). In the hypertrophied myocardium, the amplitude of [Ca 2ϩ ] i increases, 9 whereas in failing myocardium, the amplitude of [Ca 2ϩ ] i decreases. 10 -13 In most animal models of hypertrophy 8,10,11,[13][14][15] and in failing human hearts, 12,16 the duration of the whole-cell [Ca 2ϩ ] i is also prolonged. However, the precise cellular mechanisms that are responsible for changes in contractility and alterations in [Ca 2ϩ ] i are largely unknown. Identification of the cellular mechanisms that underlie altered excitation-contraction coupling in cardiac hypertrophy and heart failure is complicated by several issues, including differences in experimental animal models and disease progression. In addition, it has only recently proved possible using confocal microscopy to measure local nonpropagating elevations of Ca 2ϩ (Ca 2ϩ sparks) at the level of individual sarcomeres. [17][18][19][20][21][22] The ability to measure Ca 2ϩ sparks provides an opportunity to evaluate directly the role of sarcoplasmic reticulum (SR) Ca 2ϩ release in muscle cells from animal models associated with cardiac hypertrophy.In this study, we used laser scanning confocal microscopy and Ca 2ϩ -sensitive fluorescent indicators to detect Ca 2ϩ sparks evoked by electrical field stimulation in ventricular cells from normal rats and from spontaneously hypertensive rats (SHRs) with cardiac hypertrophy. By quantitative analysis of the kinetic characteristics of Ca 2ϩ sparks, we identify enhanced SR Ca 2ϩ release from hypertrophied SHR cells. In

Endogenous peroxidase activity in rat thyroid follicular cells is demonstrated cytochemically . Following perfusion fixation of the thyroid gland, small blocks of tissue are incubated in a medium containing substrate for peroxidase, before being postfixed in osmium tetroxide, and processed for electron microscopy . Peroxidase activity is found in thyroid follicular cells in the following sites : (a) the perinuclear cisternae, (b) the cisternae of the endoplasmic reticulum, (c) the inner few lamellae of the Golgi complex, (d) within vesicles, particularly those found apically, and (e) associated with the external surfaces of the microvilli that project apically from the cell into the colloid . In keeping with the radioautographic evidence of others and the postulated role of thyroid peroxidase in iodination, it is suggested that the microvillous apical cell border is the major site where iodination occurs . However, that apical vesicles also play a role in iodination cannot be excluded . The in vitro effect of cyanide, aminotriazole, and thiourea is also discussed .

The lung is able to rapidly remove 5-hydroxytryptamme (5-HT) from the circulation by a Na+-dependent transport mechanism. In order to identify the sites of uptake, radioautographic studies were done on rat lungs which had been isolated and perfused with 5-HT-3H and 0 5 mM iproniazid, a monoamine oxidase inhibitor. In control experiments 10-4 M imipramine was added to the perfusate to inhibit the membrane transport of 5-HT At the light microscope level, silver grains were seen concentrated near capillaries and in the endothelium of large vessels From electron microscope radioautographs a semiquantitative grain count was made and 90% of the silver grains were observed over capillary endothelial cells. The grains were found over the nucleus and cytoplasm of the cell and shewed no preferential association with any particular cytoplasmic inclusion bodies, organelles, or vesicles Other cell types were unlabeled except for a few mast cells, certain vascular smooth muscle cells, and one nerve ending. This radioautographic demonstration of the cell type responsible for the rapid removal of 5-HT from the lung circulation clearly establishes the existence of a new metabolic role for pulmonary endothelial cells.

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