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Immunohistochemical Assessment of Melatonin Binding in the Pineal Gland (1985)

Holloway, W. R. ; Grota, L. J. ; Brown, G. M.

Oxford, UK : Blackwell Publishing Ltd

Journal of pineal research 2 (1985), S. 0

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ISSN: 1600-079X

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Medicine

Notes: Melatonin binding in the pineal gland of albino rats is estimated using an immunohistochemical procedure. Binding is saturable, has relatively high affinity (Apparent KD= 2.7 nM), and competition studies indicate binding of indoleamines possessing an N-acetyl group on the terminus of the side chain (N-acetylserotonin and melatonin). These data are consistent with the interpretation that immunohistochemically determined melatonin in unfixed pineal tissue is assessing binding of N-acetylated indolealkylamines to pineal cell components.In albino rats maintained on 12-hour light: 12-hour dark cycles, melatonin binding exhibits a diurnal rhythm with low levels of saturation (30%) early in the light and saturation by endogenous melatonin near the onset of darkness. An annual rhythm of melatonin binding was observed in albino rats with low levels during the summer and high levels during the winter. Other rats were maintained on 12-hour light: dark cycles and fed for 2 hours either early in the light period or early in the dark period. For both morning- and evening-fed animals, melatonin binding was high prior to feeding and dropped immediately after feeding. Changes in melatonin binding that occur in response to alterations of feeding and time of year suggest the possibility that this binding reflects a functional site for melatonin.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1600-079X.1985.tb00643.x

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Complex Shape Changes in Isolated Rat Osteoclasts: Involvement of Protein Kinase C in the Response to Calcitonin (1997)

Holloway, W. R. ; Collier, F. M. ; Herbst, R. E. ; [et al.]

Springer

Calcified tissue international 61 (1997), S. 306-312

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ISSN: 1432-0827

Keywords: Key words: Osteoclast — Calcitonin — Protein-kinase-C — Phorbol-ester — Forskolin — Signal transduction.

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine , Physics

Notes: Abstract. The cytoplasmic spreading of osteoclasts has been used to assess responsiveness to agents such as calcitonin and associated signal transduction mechanisms. Although cyclic AMP and intracellular calcium are known mediators of calcitonin effects in osteoclasts, the role of protein kinase C (PKC) is less clear. We have used time-lapse videomicroscopy of isolated rat osteoclasts to characterize shape changes induced by calcitonin, forskolin, and phorbol 12-myristate-13-acetate (PMA) in the absence and presence of PKC blockers. Treatment with calcitonin reduced cytoplasmic plan area but increased perimeter length, resulting in a characteristic ``stellate'' appearance, whereas forskolin produced ``nonstellate'' contraction. The response of osteoclasts to PMA was dose dependent. High concentrations (10−7–10−6 M) produced biphasic responses with transitory, calcitonin-like ``stellate'' contraction followed by sustained expansion, whereas low concentrations (10−11–10−9 M) produced expansion only. The effects of low-concentration PMA could be prevented by pretreatment with a PKC blocker, whereas the effects of high concentrations were only partially inhibited. The effects of forskolin were unchanged by pretreatment with the PKC blocker. Treatment with calcitonin in the presence of various PKC blockers resulted in paradoxical transient expansion followed by contraction. These results indicate that calcitonin-induced shape change in osteoclasts is a complex process involving protein kinase C in addition to cyclic AMP-dependent mechanisms and possibly other factors.