Search PubMed⌕ Search

Biomedical subjects

K A Ryan

Publications and source records attributed to K A Ryan.

46 records · Page 3Linked to original sources
PubMed1988

A knotted free minicircle in kinetoplast DNA.

Kinetoplast DNA, the mitochondrial DNA of trypanosomes, is a network containing thousands of minicircles that are topologically interlocked. The minicircle replication intermediates are free molecules that have been released from the network. We report here that one form of free minicircles is a trefoil knot. Identification of this knotted structure is based on its electrophoretic and sedimentation properties, its response to treatments with restriction enzymes or topoisomerase II, and its appearance by electron microscopy. Except for its topology, the knotted minicircle closely resembles a previously described replication intermediate with a unique gap in the newly synthesized L strand.

Animals↗
PubMed1988

Dopamine receptors on adrenal chromaffin cells modulate calcium uptake and catecholamine release.

The presence of dopamine-containing cells in sympathetic ganglia, i.e., small, intensely fluorescent cells, has been known for some time. However, the role of dopamine as a peripheral neurotransmitter and its mechanism of action are not well understood. Previous studies have demonstrated the presence of D2 dopamine receptors on the surface of bovine adrenal chromaffin cells using radioligand binding methods and dopamine receptor inhibition of catecholamine release from perfused adrenal glands. In the present study, we provide evidence confirming a role of dopamine receptors as inhibitory modulators of adrenal catecholamine release from bovine chromaffin cell cultures and further show that the mechanism of modulation involves inhibition of stimulated calcium uptake. Apomorphine gave a dose-dependent inhibition (IC50 = 1 microM) of 45Ca2+ uptake stimulated by either nicotine (10 microM) or membrane depolarization with an elevated K+ level (60 mM). This inhibition was reversed by a series of specific (including stereospecific) dopamine receptor antagonists: haloperidol, spiperone, sulpiride, and (+)-butaclamol, but not (-)-butaclamol. In addition, the calcium channel agonist Bay K 8644 was used to stimulate uptake of 45Ca2+ into chromaffin cells, and this uptake was also inhibited by the dopamine receptor agonist apomorphine. The combined results suggest that dopamine receptors on adrenal chromaffin cells alter Ca2+ channel conductance, which, in turn, modulates catecholamine release.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1986

Ribonucleotides associated with a gap in newly replicated kinetoplast DNA minicircles from Trypanosoma equiperdum.

In Trypanosoma equiperdum, some newly replicated kinetoplast DNA minicircles contain a single gap at a unique location in their newly synthesized strand (Ntambi, J. M., and Englund, P. T. (1985) J. Biol. Chem. 260, 5574-5579). We now report that ribonucleotides are associated with this gap, with one or two covalently attached to the 5' terminus of the newly synthesized strand. There appear to be two possible RNA/DNA junctions at adjacent positions in the sequence. The ribonucleotides may be remnants of a replication primer, and their presence strongly implies that the gap is at the site of a replication origin.

Animals↗
PubMed1986

A highly bent fragment of Crithidia fasciculata kinetoplast DNA.

Kinetoplast DNA minicircles from Crithidia fasciculata contain a single major region of bent helix. Restriction fragments containing this bent helix have electrophoretic behavior on polyacrylamide gels which is much more anomalous than that of previously studied bent fragments. Therefore, the C. fasciculata fragments probably have a more extreme curvature. Sequencing part of a cloned minicircle revealed an unusual structure for the bent region. In a sequence of 200 bases, the bent region contains 18 runs of 4-6 As with 16 of these runs in the same strand. In some parts of this sequence the A runs are regularly spaced with a periodicity of about 10 base pairs. This spacing is nearly in phase with the twist of the DNA helix. This same sequence arrangement has been observed in other bent fragments, but the number of A runs is much greater in this C. fasciculata sequence. It is likely that there are small bends associated with each A run which, because of their periodic spacing, add up to produce substantial curvature in this molecule. In addition to having highly anomalous electrophoretic behavior, the fragment has unusual circular dichroism spectra. Its spectrum in the absence of ethanol is that of B DNA, but ethanol in the concentration range of 51-71% (w/w) induces changes to forms which are different from those of any well characterized DNA structure. The C. fasciculata bent helix is neither cleaved by S1 nuclease nor modified by bromoacetaldehyde under conditions in which other unusual DNA structures (such as cruciforms or B-Z junctions) are susceptible to attack by these reagents. Finally, a two-dimensional agarose gel analysis of a family of topoisomers of a plasmid containing the bent helix revealed no supercoil-induced relaxation.

Animals↗
PubMed1984

Presence of a bent helix in fragments of kinetoplast DNA minicircles from several trypanosomatid species.

Some restriction fragments of kinetoplast minicircles from several trypanosomatid species (Leishmania tarentolae, Trypanosoma brucei, T. equiperdum, Herpetomonas muscarum, Crithidia fasciculata, but not T. cruzi) migrate anomalously on polyacrylamide gels. This behavior is probably due to a natural curvature of the helix. Bent helices appear to be a common property of kinetoplast minicircles, and may be important for minicircle function. In the case of T. equiperdum, we present evidence that each minicircle has a single bent region which resides in or near the 'conserved sequence.'

Animals↗
PubMed1983

[Bacteriological study of bivalves of the Gulf of Nicoya, Costa Rica. II. State of the mollusk at the time of eating it].

In a sanitary survey, nine taverns were chosen among those selling mollusk coctails, eaten raw, in the city of San José so as to represent three socio-economic levels. Sixty-six samples of coctails were examined for total and fecal coliforms, Staphylococcus aureus, and salmonellas. Only 7% of the samples proved to be within the accepted limits for human consumption. No correlation was found between sample origin and its bacteriologically determined quality.

Costa Rica↗
PubMedDate not supplied

Standardized care plans for i.v. therapy.

The use of standardized care plans by nurses has become an efficient tool for communicating special needs of patients. We at Good Samaritan Hospital and Medical Center recognized that our I.V. Team and the patients we service could benefit from the use of such a care plan. Improved communication and documentation were accomplished by developing a standard care plan addressing problems that may be encountered in I.V. therapy. This form has become a valuable part of our care to patients receiving I.V. therapy.

Humans↗
PubMedDate not supplied

Amphotericin B infused in 20% lipid emulsion.

Amphotericin B has been associated with multiple adverse effects; however, clinically it may be the best or only drug of choice for certain infections. This antifungal has traditionally been administered in D5W solutions over 4 to 6 hours with pre- and/or post-hydration and other medications to minimize the renal toxicity and other side effects. There have been studies using amphotericin infused in a 20% lipid emulsion with the hope of decreased side effects. By changing the diluent to lipids, the volumes to be infused over shorter periods was a challenge. This article will examine administration protocols of the D5W mixture and the lipids emulsion solution and does not advocate the use of lipid solutions.

Amphotericin B↗