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D E Knight

Publications and source records attributed to D E Knight.

69 records · Page 4Linked to original sources
PubMed1981

Calcium control of exocytosis and endocytosis in bovine adrenal medullary cells.

Experimental analysis of the mechanisms of exocytosis and endocytosis has hitherto been hampered by the inaccessibility of the intracellular sites at which they are controlled. We have recently developed a technique that overcomes this problem. Cells are subjected to intense electric fields of brief duration; this renders the plasma membrane permeable without impairing its ability to participate in exocytosis and endocytosis. Working with 'leaky' bovine adrenal medullary cells, catecholamine release has a rather specific requirement for Mg-ATP, is activated by micromolar concentrations of ionized Ca and can be inhibited by Mg, detergents, trifluoperazine, high osmotic pressure and various anions. The mechanism of activation by Ca is discussed in some detail.

Adenosine Triphosphate↗
PubMed1980

Gaining access to the site of exocytosis in bovine adrenal medullary cells.

1. A new technique is described for gaining access to the intracellular site at which exocytosis is controlled. By exposing isolated cells to high electric fields of brief duration, it is possible to create "leaky" cells in which the plasma membrane has been by-passed without impairing the ability of the cells to undergo exocytosis. 2. In the presence of EGTA and an ionized Ca of less than 10(-8) M, "leaky" cells lose less than 1% of their total catecholamine. When exposed to 10 microM ionized Ca they lose up to 30% of their catecholamine together with dopamine-beta-hydroxylase but no lactate dehydrogenase. The time course of release of both catecholamine and dopamine-beta-hydroxylase are identical, suggesting that release must involve exocytosis. Exocytosis in these "leaky" cells has the following properties: A) It is half maximal in the presence of a buffered ionized Ca of approximately 1 microM. Millimolar concentrations of Mg reduce both the affinity for Ca and also the total amount of catecholamine released at high calcium concentrations. B) It has a specific requirement for Mg ATP. C) It is inhibited by a variety of anions. The most potent inhibitor is SCN, and the least glutamate and acetate. D) It is inhibited by the anti-psychotic drug trifluoperazine.

Adenosine Triphosphate↗
PubMed1975

External otitis among swimmers and nonswimmers.

Studies were undertaken between the summers of 1970 and 1974 to determine the effects of swimming on the incidence of external otitis and on the isolation of Pseudomonas aeruginosa from infected outer ears. The frequency of "earaches" reported by swimmers during a telephone survey conducted during the summer of 1971 was 2.4 times the frequency reported by nonswimmers. Furthermore, the risk of a swimmer acquiring external otitis, determined from reports of outer-ear infections received from physicians during the same period, was approximately five times as great as the risk to nonswimmers. Swimming also increased the risk of P aeruginosa involvement in otitis externa, and reported infections among swimmers tended to be more severe than infections among nonswimmers.

Environmental Exposure↗
PubMedDate not supplied

Cyclic nucleotides control a system which regulates Ca2+ sensitivity of platelet secretion.

Cellular responses to extracellular signals are mediated by changes in the intracellular concentrations of one or more second messengers. In platelets, inhibitory agonists increase intracellular cyclic-3',5'-AMP [( cyclic AMP]i (refs 2, 3] whereas excitatory agonists increase [Ca2+]i and/or [1,2-diacylglycerol]i (refs 4-9), and in some cases decrease [cyclic AMP]i (refs 10, 11). Both activation and inhibition of platelet responses have been attributed to an increase in [cyclic-3',5'-GMP]i (refs 8, 12). The activity of protein kinase C, which is associated with the platelet secretory response, is increased by both 1,2-diacylglycerol and Ca2+ (refs 4, 7, 8). The role of cyclic AMP may involve either inhibition of Ca2+ mobilization to the cytosol or stimulation of intracellular Ca2+ uptake, and in addition inhibition of 1,2-diacylglycerol formation. The relationship between cyclic-3',5'-GMP (cyclic GMP) and other second messengers in platelet activation has not been defined. Using platelets made permeable by exposure to an intense electric field, we demonstrate here modulation of the Ca2+ sensitivity of platelet secretion by thrombin, and by 12-O-tetradecanoylphorbol-13-acetate (TPA) and 1-oleyl-2- acetylglycerol ( OAG ), both potent activators of protein kinase C. The effect of thrombin is selectively modified by cyclic GMP and cyclic AMP. The response to OAG and TPA is also modulated by cyclic AMP but to a much lesser extent.

1-Methyl-3-isobutylxanthine↗
PubMedDate not supplied

Inhibition of exocytosis in bovine adrenal medullary cells by botulinum toxin type D.

Botulinum toxins are known to block transmitter release at peripheral cholinergic synapses, producing muscular weakness and paralysis. The toxins may also block adrenergic transmission, although this effect is less well understood. The mechanisms by which toxins act are unclear. They are proteins of relative molecular mass approximately 150,000 and are structurally similar to tetanus toxin. It is generally accepted that a rise in intracellular calcium concentration is sufficient to trigger secretion by exocytosis, but it is not known whether the toxins block secretion by preventing this Ca transient or whether they act downstream from Ca entry by interfering with the process of exocytosis itself. We have attempted to resolve these questions in the case of the adrenergic system by studying the effects of botulinum toxins (types A, B, D and E) on the secretory response of isolated bovine adrenal medullary cells maintained in culture. The cells were either challenged with various secretagogues or rendered leaky and challenged directly with Ca buffers. We report here that botulinum toxin type D inhibits secretion in a time- and dose-dependent manner, the results being entirely consistent with the idea that the toxin acts at or near the site of exocytosis rather than at the sites controlling the rise in free Ca.

Acetylcholine↗