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Active calcium ion transport in Xenopuslaevis skin (1997)

Guirguis, S. M. E. ; Yee, J. C. ; Stiffler, D. F.

Springer

Journal of comparative physiology 167 (1997), S. 328-334

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ISSN: 1432-136X

Keywords: Key wordsApical calcium channels ; Nifedipine ; Diltiazem ; Verapamil ; L-channels ; Lanthanum ; Cobalt ; Nickel

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine

Notes: Abstract The skin of intact, free-swimming Xenopus laevis transports Ca2+ inwardly in a manner that is proportional to the external [Ca2+] up to about 0.3 mmol · l−1, saturates above 0.3 mmol · l−1, and is opposed to the electrochemical gradient. Efflux is relatively constant at external concentrations between 0.016 and 0.6 mmol · l−1; net flux which is negative below 0.125 mmol · l−1 becomes positive above this external [Ca2+]. Allometric analysis suggests that both Ca2+ influx and efflux scale to the 2/3 power approximately like surface area. There were no significant differences in influx between summer and fall animals; however, efflux was greater in the fall and this resulted in a change from positive balance in the summer to negative balance in the fall. Isolated skins were shown to support a Ca2+ uptake rate of nearly 30 nmol · cm−2 · h−1. The phenylalkylamine verapamil in the apical bathing solution significantly inhibited this at 25 μmol · l−1. The benzothiazepine diltiazem was also effective at 50 μmol · l−1 while the dihydropyradine nifedipine was ineffective up to 100 μmol · l−1. The inorganic ion La3+ was effective at blocking Ca2+ uptake at 300 μmol · l−1; Ni2+ was also effective at 500 μmol · l−1 but Co2+ was ineffective up to 500 μmol · l−1. These results suggest that apical calcium channels in Xenopuslaevis skin have properties similar to mammalian L-channels and fish gill Ca2+ channels.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s003600050081

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Hypophysial portal vascular infusion of TRH in the rat: An ultrastructural and radioimmunoassay studySupported in part by NIH Biomedical Research Support Grant RR05420 to the Medical University of South Carolina and by the South Carolina State Appropriation for Biomedical Research. (1978)

Wilbur, D. L. ; Yee, J. A. ; Raigue, S. E.

New York, NY [u.a.] : Wiley-Blackwell

American Journal of Anatomy 151 (1978), S. 277-293

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ISSN: 0002-9106

Keywords: Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Medicine

Notes: The hypophysial portal vessels and anterior pituitary gland of adult male Wistar rats were exposed surgically. A hypophysial portal vessel was cannulated and infused for one minute with saline or thyrotrophin (TRH). Anterior pituitary glands were collected at 1, 5, 15, 30, or 60 minutes after cessation of infusion, for light and electron microscopic examination. Before and immediately after cannulation of a portal vessel, a 1-ml sample of blood was collected at 1, 5, 15, 30, or 60 minutes, from the femoral vein for radioimmunoassay (RIA) of growth hormone. Thyrotrophs from anterior pituitary glands of rats infused with TRH displayed emiocytic activity at all time-periods studied. Rough endoplasmic reticular (RER) cisternae were dilated at 15 minutes following infusion and remained dilated at 30 and 60 minutes. TRH was observed to stimulate emiocytic activity in most pituitary cell-types. Extensive dilations of RER cisternae were also observed in mammotrophs and gonadotrophs, but were not observed in somatotrophs or adrenocorticotrophs. The demonstration that thyrotrophs, mammotrophs, somatotrophs, and gonadotrophs respond to TRH suggests that some common features may be shared by these cells. Preliminary analysis of the RIA data show that TRH was potent in elevating radioimmunoassayable growth hormone levels. Significant increases (p 〈 0.02) in plasma GH levels were present at the earlier time periods studied (1, 5, and 15 minutes) following the infusion of TRH, but not at 30 or 60 minutes. These findings provide additional support for the non-specific action of TRH upon the various adenohypophysial cell types, and demonstrate that TRH stimulates these cells by a direct action on the adenohypophysis.

Additional Material: 2 Tab.