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Membrane Potential and Catecholamine Secretion by Bovine Adrenal Chromaffin Cells: Use of Tetraphenylphosphonium Distribution and Carbocyanine Dye Fluorescence (1985)

Friedman, J. E. ; Lelkes, P. I. ; Lavie, E. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Journal of neurochemistry 44 (1985), S. 0

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ISSN: 1471-4159

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Medicine

Notes: Abstract: Changes in plasma membrane potential of isolated bovine adrenal chromaffin cells were measured independently by two chemical probe methods and related to corresponding effects on catecholamine secretion. The lipophilic cation tetraphenylphosphonium (TPP+) and the carbocyanine dye 3,3′-dipropylthiadicarbocyanine [DiS-C3-(5)] were used. The necessity of evaluating the subcellular distribution of TPP+ among cytoplasmic, mitochondrial, secretory granule, and bound compartments was demonstrated and the resting plasma membrane potential determined to be – 55 mV. The relationship between membrane potential and catecholamine secretion was determined in response to variations in extracellular K+ and to the presence of several secretagogues including cholinergic receptor ligands, veratridine, and ionophores for Na+ and K+. The dependence of potential on K+ concentration fit the Goldman constant field equation with a Na/K permeability ratio of 0.1. The dependence of both K+ - and veratridine-evoked catecholamine secretion on membrane potential exhibited a potential threshold of about – 40 mV before a significant rise in secretion occurred. This is likely related to the threshold for opening of voltage-sensitive Ca2+ channels. Acetylcholine and nicotine evoked a large secretory response without a sufficiently sustained depolarization to be detectable by the relatively slow potential sensitive chemical probes. Decamethonium induced a detectable depolarization of the chromaffin cells. Veratridine and gramicidin evoked both membrane depolarization and catecholamine release. By contrast the K ionophore valinomycin evoked significant levels of secretion without any depolarization. This is consistent with its utilization of an intracellular source of Ca2+ and the independence of its measured secretory response on extracellular Ca2+

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1471-4159.1985.tb08775.x

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125Iodine decay in DNA: A discussion of its effectiveness for the breaking of DNA strands (1987)

Tisljar-Lentulis, G. ; Schneeweiss, F. H. A. ; Feinendegen, L. E.

Springer

Radiation and environmental biophysics 26 (1987), S. 189-195

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ISSN: 1432-2099

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Physics

Notes: Summary 125I incorporated in DNA is known to be exceptionally toxic. Values of D0 range from about 40 to about 90 decays for survival of mammalian cells. The effectiveness of125I in DNA with respect to the induction of breaks of the DNA strands, however, appears to be comparatively low. The numbers of strand breaks per energy deposited in subnuclear cellular structures such as DNA is smaller for a disintegration of125I than forγ-rays. The difference in effectiveness diminishes with increasing mass of the considered sensitive volume. The apparent inefficiency of125I-decay may, on one hand, result from a waste of local energy deposition. On the other hand, it may be caused by a multitude of local strand breaks (clusters) induced by125I-decay which are measured as one break only by the conventionally applied techniques of strand break measurement. The apparent inefficiency of125I may be evidence furthermore for the importance of considering not only the DNA as the sensitive target but with equal pertinence the gross sensitive volume, i.e. the whole cell nucleus [12]. Further, for drawing meaningful comparisons, it may be necessary to take into consideration the microdosimetric event size distributions for the critical targets [1].