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Biomedical subjects

S A Little

Publications and source records attributed to S A Little.

67 records · Page 4Linked to original sources
PubMed1981

A 45Ca autoradiographic and stereological study of freeze-dried smooth muscle of the guinea pig vas deferens.

In an effort to more clearly elucidate the role of cellular structures as calcium sinks and sources in smooth muscle cells, the intracellular distribution of radioactive calcium was evaluated by a new method based on freeze-drying. The guinea pig vas deferens was exposed to a physiological salt solution that contained 45Ca. The muscle was then freeze-dried and prepared for electron microscope autoradiography. The grain density over the plasma membrane, mitochondria, and sarcoplasmic reticulum (SR) was significantly greater than that of the matrix. These results suggest that the plasma membrane, mitochondria and SR have the capacity to accumulate calcium. Which of these structures serve as a source of calcium for contraction remains to be determined. A stereological comparison between freeze-dried and conventionally prepared smooth muscles revealed several differences. The cross-sectional area of freeze-dried cells was about twice that of conventionally prepared cells. Moreover, mitochondria and sub-surface vesicles occupied a significantly smaller percentage of the cell in the freeze-dried tissue than they did in the conventionally prepared tissue.

Animals↗
PubMed1980

Effects of hydrogen peroxide on basal and hormone-stimulated lipolysis in perifused rat fat cells in relation to the mechanism of action of insulin.

Since insulin is known to stimulate intracellular hydrogen peroxide production in rat epididymal fat cells, the effects of exogenous hydrogen peroxide on rates of basal and hormone-stimulated lipolysis were investigated in a perifusion system. H2O2 (60 microM) caused a weak and transient stimulation of basal lipolysis that did not interfere with subsequent activation of lipolysis by hormones. More importantly, lipolysis stimulated submaximally with ritodrine (10(-7) M) or glucagon (10(-9) M) was inhibited by H2O2 in a manner similar to insulin, although slight differences in time course were noted. Ritodrine served as a beta-adrenergic agonist resistant to oxidative destruction by H2O2. The inhibition of lipolysis was reversible upon cessation of perifusion with H2O2. These findings ruled out oxidative destruction of the hormone or cell death as explanations for the antilipolytic effect of H2O2. Like insulin, H2O2 also inhibited 1-methyl-3-isobutylxanthine (4 X 10(-6) M)-stimulated lipolysis, but whereas insulin inhibited lipolysis stimulated by dibutyryl-cAMP (4 X 10(-4) M), H2O2 further enhanced it. These findings add another case to the growing list of insulin effects on adipocytes that can be mimicked by exogenous H2O2, and they hint at a site where the mechanisms of action of the two agents may differ.

1-Methyl-3-isobutylxanthine↗
PubMed1979

Ultrastructural characteristics of freeze-dried smooth muscle.

The rapid freezing and vacuum dehydration of tissue has been employed to study the intracellular distribution of diffusible substances at the electron microscopic level. Hower, the ultrastructural detail of freeze-dried tissue is difficult to retain. Consequently, the ultrastructural preservation of freeze-dried smooth muscle has not been sufficient to permit satisfactorily definition of intracellular organelles. Therefore, determinations of the intracellular distribution of soluble ions have not been achieved in freeze-dried smooth muscle. In this study a freeze drying method is presented which provides more satisfactory definition of intracellular organelles than has been available in the past. Using this merens have been preserved. When these muscles are compared to convention preparer of surface vesicles that are observed, and the mitochondria are extremely electron opaque in the freeze-dried tissue. The smooth muscles which have been examined do not have the inherent contrast of other types of tissue nor do they contain the different types of mitochondria that have been observed in nonmuscle tissue.

Animals↗
PubMed1978

Characterization of proinsulin-insulin intermediates in human plasma.

This work addressed the problem of heterogeneity of immunoreactive insulin (IRI) in human plasma. Subjects with normal glucose tolerance were given 75g of an oral glucose solution, followed in 30 min by an intravenous infusion of 30g of arginine over 30 min. At the end of the infusion blood was withdrawn for analysis. IRI was extracted from plasma of individual subject by immunosorbent columns and was fractionated by gel filtration, disc gel electrophoresis and isoelectric focusing. Human IRI components were identified by molecular size, immunoreactivity with a human proinsulin antibody, sensitivity to trypsin, and by comparison of electrophoretic mobility and isoelectric point with porcine pancreatic products, after suitable correction for electric charge and molecular weight differences. The pattern of IRI heterogeneity was the same among six healthy subjects. Heterogeneity of proinsulin-size IRI in circulation was more marked than that of insulin-size material. Proinsulin and desdipeptide proinsulin were present in approximately equal amounts accompanied by minor amounts of split proinsulin and monodesamido-desdipeptide proinsulin. Insulin-size IRI contained over 80% insulin. Minor amounts of monodesamidoinsulin and diarginylinsulin were observed in some cases. The types of IRI components observed in plasma are evidence in support of a physiologic role of trypsin-and carboxypeptidase B-like enzymes in the conversion of proinsulin to insulin. Moreover, this study provides a base line for investigation of abnormalities in proinsulin-to-insulin conversion that may be associated with certain pathologic states.

Humans↗