Biomedical subjects

J B Reed

Publications and source records attributed to J B Reed.

36 records · Page 2Linked to original sources

PubMed1988

Effects of membrane potential on electrical slow waves of canine proximal colon.

The effects of membrane potential on the waveforms and propagation of slow waves were tested using circular muscles of the canine colon. Studies were conducted with intracellular recording techniques on cross-sectional strips of canine proximal colon. Circular muscle cells near the submucosa generated slow waves that decayed in amplitude as they spread through the circular layer. The membrane potentials of cells were less negative as a function of distance from the submucosal border. Cells near the submucosa were depolarized with elevated external K+ and electrical pulses using the partitioned chamber technique. The waveforms of depolarized submucosal cells were compared with events recorded from cells in the bulk of the circular layer. The waveform changes caused by experimental depolarization were different from the changes in waveform that occur during propagation, suggesting the latter are due to a different mechanism than depolarization. The effects of the membrane potential on syncytial input resistance and length constant were also evaluated. The results of these studies are consistent with the hypothesis that slow-wave propagation across the circular layer in canine proximal colon occurs passively.

Animals↗

PubMed1987

Origin and propagation of electrical slow waves in circular muscle of canine proximal colon.

Experiments to determine the site of slow-wave origin and the mechanism of propagation were performed on muscles of the canine proximal colon. Cells along the submucosal border of the circular layer had resting membrane potentials (RMP) averaging -78 mV, and slow waves, 40 mV in amplitude. The RMP of cells through the thickness of the circular layer decreased exponentially with distance from the submucosal border, such that RMPs of circular cells at the myenteric border were only -43 mV. Slow waves decreased in amplitude through the thickness such that slow waves could not be detected adjacent to the myenteric border. When a thin strip of muscle along the submucosal border was removed, slow waves were not recorded from the bulk of the circular layer and could not be evoked by acetylcholine. Slow waves were still present in the excised strip. Experiments to determine the rate of slow-wave propagation were also performed. Two cells were impaled, one at the submucosal surface, and another at some distance through the circular layer. Slow waves occurred nearly simultaneously at both sites. What latency was observed could be explained on the basis of electrotonic conduction. The results support the hypothesis that in the canine proximal colon slow waves are generated at the extreme submucosal surface of the circular layer. The bulk of the circular layer does not possess either pacemaker or regenerative mechanisms, and slow waves propagate passively toward the myenteric border. The cable properties of the circular muscle syncytium furnish a barrier to invasion of the longitudinal layer by the slow wave event.

Acetylcholine↗

PubMed1987

Interaction of two electrical pacemakers in muscularis of canine proximal colon.

Experiments were performed to determine the source of the 20 cycles/min electrical oscillation commonly seen in colonic electrical records, the influence of the 20 cycles/min rhythm on the circular and longitudinal muscle layers, and the interactions between the 20 cycles/min rhythm and slow waves in circular muscle cells. Cross-sectional muscle preparations of the canine proximal colon were used to allow impalement of cells at any point through the thickness of the muscularis. Intracellular recordings from circular muscle cells clearly showed the two characteristic pacemaker frequencies in the colon (6 cycles/min slow waves; 20 cycles/min oscillations). The 20 cycles/min oscillations were recorded from longitudinal and circular muscle cells. Their amplitudes were greatest at the myenteric border. In the longitudinal layer the 20 cycles/min events initiated action potentials; in circular muscle the 20 cycles/min events summed with slow waves. Simultaneous recordings from circular and longitudinal cells across the myenteric border demonstrated that events in the two layers were usually in phase, suggesting that the two layers are electrically coupled and are paced by a common pacemaker. The amplitude of the 20 cycles/min events decayed with distance from the myenteric border in both circular and longitudinal muscles. The data demonstrate that two discrete populations of pacemaker cells generate the spontaneous electrical activity in the colon. Both events appear to passively spread through the circular muscle. It is the summation of these events that appears to serve as the signal for excitation-contraction coupling in circular muscle.

Animals↗

PubMed1985

Electrical basis for the effects of ethyl alcohol on canine gastric corpus muscles.

The effects of ethyl alcohol (EtOH) on membrane potential and slow wave activity were tested in strips of canine corpus circular muscle. Previous studies have shown that EtOH (0.1-1%) reduced the force and frequency of phasic contractions of corpus muscles and increased tone. It was the intention of this study to determine whether the mechanical effects were due to an electrical mechanism. Intracellular recordings revealed that EtOH hyperpolarized resting membrane potential and reduced the amplitude, duration and frequency of slow waves. These changes were concentration-dependent over the same range of EtOH concentrations that inhibited phasic mechanism activity. Simultaneous recordings of force and membrane potential demonstrated these effects. The tone produced by corpus muscles exposed to EtOH could not be explained by an electrical mechanism. The fact that membrane potential and several parameters of the slow wave depolarization are affected by EtOH might be explained by an increase in membrane conductance produced by EtOH.

Animals↗

PubMed1985

Slow wave heterogeneity within the circular muscle of the canine gastric antrum.

A cross-sectional preparation was designed in which multiple micro-electrodes can be precisely positioned to impale smooth muscle cells anywhere from the serosa to the submucosa. Intracellular electrical recordings were obtained from gastric antral circular muscle cells from the myenteric plexus to the submucosa. The resting membrane potential changed linearly as a function of distance from the myenteric plexus to the submucosa. Slow wave upstroke dV/dt, upstroke potential amplitude, and plateau potential amplitude changed linearly as a function of distance from the myenteric plexus to the submucosa. When slow waves were recorded simultaneously from a circular cell near the myenteric plexus and from a cell near the submucosa, the event always occurred first in the cell near the myenteric plexus. Electrical differences did not appear to be caused by electrotonic decay of slow waves as they propagated through the circular muscle. Electrical differences could not be explained on the basis of differences in intrinsic neural activity or prostaglandin synthesis. Membrane polarization could not explain the differences in slow waves between myenteric and submucosal circular muscle cells. The conclusion of this paper is that fundamental differences exist between the excitability mechanisms and/or passive membrane properties of cells near the myenteric plexus and the submucosa. These differences might be manifest in different motor performance of these two muscle cell populations.

Action Potentials↗

PubMed1979

Reye's syndrome.

Explore the source record for details and available documents.

Brain↗

PubMed1977

Haemorrhagic syndrome of cattle of suspected mycotoxic origin.

An outbreak of disease characterised by haemorrhages, anaemia, leucopenia, thrombocytopenia, skin lesions, degenerative and inflammatory tissue changes and death was investigated in herd of dairy cows. A tentative diagnosis based on circumstantial evidence was of mycotoxicosis arising from the feeding of mouldy barley.

Animal Feed↗

PubMed1976

Vectorcardiographic criteria for the diagnosis of anterior myocardial infarction.

Frank lead vectorcardiograms (VCG) from four carefully selected patient subgroups (226 patients) were analyzed to develop optimal criteria for the diagnosis of anterior myocardial infarction. Specificity was evaluated using 100 healthy volunteers under age 30 and 80 patients with normal left ventriculogram and normal coronary arteriograms. Sensitivity was determined using 25 patients with evolutionary ST-T wave changes (V1-2), and LDH and CPK isoenzyme evidence of acute myocardial infarction; and 21 patients with anterior wall akinesia or dyskinesia and greater than 70% occlusion of the left anterior descending coronary artery. Patients with VCG evidence of bundle branch block, left or right ventricular hypertrophy were excluded. The criterion for the diagnosis of anterior myocardial infarction which was found to give the highest sensitivity with greater than or equal to 95% specificity was: initial anterior QRS forces must not exceed 0.1 mV in maximal anterior amplitude and also must not exceed 24 msec in duration. The performance of this proposed criterion was then tested using four similarly defined patient subgroups consisting of a total of 222 patients. The incidence of false positive diagnosis in these test subgroups was less than 1% with a sensitivity of greater than 95%. The overall performance of the proposed criterion was found to be significantly superior to both the widely accepted VCG and ECG criteria for anterior myocardial infarction. Thus, this quantitative criterion using both time and duration of initial anterior forces is both a highly specific and a sensitive indicator of anterior myocardial infarction.

Adult↗

PubMed1976

Paecilomyces varioti endocarditis on a prosthetic aortic valve.

Fungal endocarditis following prosthetic valve surgery has assumed increased importance as a cause of postoperative death. We present, to our knowledge, the first case of the fungus Paecilomyces varioti producing endocarditis on a prosthetic aortic valve. This seems to be an extremely indolent organism which exhibits an apparent response to antibiotic therapyl. In vitro evidence suggests that this fungus is sensitive to attainable serum levels of both 5-fluorocytosine and amphotericin B. However, after viewing the extracted valve and the devastating embolic phenomenon in our patient, we believe that medical therapy alone would not suffice. Thus we suggest that prompt valve replacement be performed in future cases.

Aortic Valve↗

PubMed1974