Search PubMed⌕ Search

Biomedical subjects

C D Johnson

Publications and source records attributed to C D Johnson.

At least 325 records · Page 18Linked to original sources
PubMed1985

Localization of choline acetyltransferase within identified motoneurons of the nematode Ascaris.

Choline acetyltransferase (CAT) activity has been measured in the nematode Ascaris lumbricoides. Strips of hypodermal tissue which contained branches of single identified motoneurons (Stretton, A.O.W., R.M. Fishpool, E. Southgate, J.E. Donmoyer, J.P. Walrond, and I.S. Kass (1978) Proc. Natl. Acad. Sci. U.S.A. 75: 3493-3497) as well as control strips containing no neural tissue were assayed. In strips of hypodermis which contained branches of excitatory motoneurons (classes DE1, DE2, and DE3), CAT activity was elevated 5 to 10 times compared to control levels. Branches of inhibitory motoneurons (classes D1 and V1) did not add to the level of CAT observed in the controls. These data provide additional support for the suggestion (e.g., del Castillo, J., W.C. deMello, and T. Morales (1963) Experientia 20: 141) that acetylcholine is an excitatory neurotransmitter at nematode neuromuscular junctions. The function of the low level of CAT observed throughout the hypodermis is unknown.

Animals↗
PubMed1984

Massive hemorrhage in an ileal duplication cyst.

We have described massive intermittent intestinal hemorrhage due to a vascular anomaly in an ileal duplication cyst in a 30-year-old man. This unusual case illustrates that these lesions disguise themselves symptomatically and must be considered in the differential diagnosis of gastrointestinal bleeding.

Adult↗
PubMed1984

Vagal influence on exocrine pancreas of alcohol-fed and of normal dogs.

A histochemical study has indicated increased activity of acetylcholine in the pancreas of chronic alcoholic dogs, and we have recently reported decrease pancreatic responsiveness to cholinergic stimulation in such dogs. This prompted us to determine, in chronic alcoholic dogs, the net pancreatic response to stimulation mediated by cholinergic nerves. Therefore, the pancreatic response to vagal stimulation by intravenous 2-deoxy-d-glucose (2DG) infusion was examined in such dogs and in controls. After 2DG, 100 mg kg-1, significant and similar increases in protein output up to maximally 2.7 +/- 0.8 and 2.3 +/- 0.5 mg kg-1 (15 min)-1 were observed in control and alcohol-treated dogs. A significant rise in flow rate and HCO-3 output up to maximally 0.26 +/- 0.07 ml kg-1 (15 min)-1 and 43 +/- 13 mumol kg-1 (15 min)-1, respectively, occurred in the controls but was delayed in the alcoholics. The finding in alcoholic dogs of no change in protein response to 2DG is not in favour of a primary increase of vagally mediated pancreatic protein secretion. It could, however, be compatible with a primary increase in cholinergic receptor resistance due to alcohol and secondary adaptive increase in cholinergic activities, which when combined, would yield no net change of the cholinergically mediated protein response.

Acetylcholine↗
PubMed1983

Multiple molecular forms of acetylcholinesterase in the nematode Caenorhabditis elegans.

Extracts of the nematode Caenorhabditis elegans contain five molecular forms of acetylcholinesterase (AChE) activity that can be separated by a combination of selective solubilization, velocity sedimentation, and ion-exchange chromatography. These are called form IA (5.2s), form IB (4.9s), form II (6.7s), form III (11.3s), and form IV (13.0s). All except form III are present in significant amounts in rapidly prepared extracts and are probably native; form III is probably derived autolytically from form IV. Most of forms IA and IB can be solubilized by repeated extractions without detergent, whereas forms II, III, and IV require detergent for effective solubilization and may therefore be membrane-bound. High salt concentrations are not required for, and do not aid in, the solubilization of these forms. For all forms, molecular weights and frictional ratios have been estimated by a combination of gel permeation chromatography and velocity sedimentations in both H2O and D2O. The molecular weight estimates range from 83,000 to 357,000 and only form II shows extensive asymmetry. The separated forms have been characterized with respect to substrate affinity, substrate specificity, inhibitor sensitivity, thermal inactivation, and detergent sensitivity. Judging by these properties, C. elegans is like other invertebrates in that none of its cholinesterase forms resembles either the "true" or the "pseudo" cholinesterase of vertebrates. However, internal comparison of the C. elegans forms clearly distinguishes forms IA, III, and IV as a group from forms IB and II; the former are therefore designated "class A" forms, the latter "class B" forms. Genetic evidence indicates that separate genes control class A and class B forms, and that these two classes overlap functionally. Several factors, including kinetic properties, molecular asymmetry, molecular size, and solubility, all suggest that a molecular model of the multiple cholinesterase forms observed in vertebrate electric organs probably does not apply in C. elegans. Potential functional roles and subunit structures of the multiple AChE forms within each C. elegans class are discussed.

Acetylcholinesterase↗
PubMed1983

Atrial pacing by a ventricular-inhibited (VVI) myocardial unipolar pacemaker.

A patient with sinoatrial node disease is reported who demonstrated inadvertent atrial pacing from a ventricular unipolar myocardial electrode and a VVI Intermedics pacemaker. Atrial refractory and vulnerable periods are addressed in this context as possibly providing the environment for an atrial arrhythmia, secondary to competition between the non-sensed impulse and the unipolar cathodal stimulus falling in the atrial vulnerable period.

Aged↗