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Biomedical subjects

M E Holman

Publications and source records attributed to M E Holman.

At least 19 recordsLinked to original sources
PubMed1987

Membrane properties of rabbit basilar arteries and their responses to transmural stimulation.

Changes in membrane potential of rabbit basilar arteries were recorded in response to transmural stimuli applied by means of a suction electrode. Responses to current pulses of long duration and low intensity showed that the passive electrical properties of basilar arteries were similar to those of other vascular smooth muscles. In contrast to peripheral arteries, action potentials were readily evoked by depolarizing currents. Action potentials were graded in amplitude from 17-60 mV according to stimulus strength. Amplitudes and rates of rise of the directly evoked action potentials increased with increasing external calcium and were abolished by cobalt, manganese and magnesium. Brief electrical stimuli which might have been expected to activate perivascular nerves produced slow depolarizing responses whose amplitude and duration increased with increasing stimulus intensity. These responses were not blocked by tetrodotoxin, lowered external calcium, or sympathetic denervation. They do not appear to be due to the release of a conventional neurotransmitter.

Animals↗
PubMed1979

Some properties of the excitatory junction potentials recorded from saphenous arteries of rabbits.

1. Excitatory junction potentials (e.j.p.s) were recorded from smooth muscle cells of the saphenous arteries of young rabbits. 2. The amplitudes of e.j.p.s recorded from different preparations, in response to a single maximal stimulus, were small and variable (5--14 mV). They decayed exponentially with a time constant of about 200 msec. 3. At frequencies greater than 1 Hz the shape of those e.j.p.s which exceeded 12--15 mV in amplitude was changed. The early part of the e.j.p.s became faster in time course. 4. Trains of up to five stimuli, at frequencies greater than 4 Hz, caused summation of e.j.p.s; 'active responses' were superimposed on this depolarization. Peak amplitude of the response to repetitive stimulation was 50 mV. 5. In normal solution, contraction appeared to be associated with a change in the configuration of e.j.p.s. 6. No action potentials resembling those recorded from most visceral smooth muscles were observed in normal solutions although these could be evoked in the presence of TEA (2.5--10 mM). 7. The method of Abe & Tomita (1968) was used to determine the values of the length constant (lambda) and time constant (tau) of the smooth muscle of intact arteries. The value of lambda (0.6 mm) was about half that found for circular strips cut from larger arteries. 8. The time constant of decay of single e.j.p.s of less than 12 mV in amplitude was indistinguishable from the membrane time constant. 9. Noradrenaline caused contraction of the artery in the absence of a change in membrane potential. 10. It is tentatively suggested that there may be two different populations of receptors in this smooth muscle membrane.

Action Potentials↗
PubMed1977

Some properties of the smooth muscle of mouse vas deferens.

1. Contractions of the mouse vas deferens in response to electrical stimulation differ form those recorded form the guinea-pig vas deferens in that they are abolished by tetrodotoxin. 2. Changes in membrane potentials were recorded form the smooth muscle of both preparations in response to stimulation with current pulses applied by an intracellular electrode and by alrge extracellular plate electrodes. 3. Both preparations behaved similarly in response to intracellular stimulation. Electrotonic potentials in response to extracellular current pulses spread in a longitudinal direction in the guinea-pig vas deferens in accordance with the cable-like properties of this preparation. In contrast, no longitudinal spread of eletrotonus was observed in the mouse vas deferens. 4. Responses to nerve stimulation differed in the two preparations. In the guinea-pig, single stimuli caused excitatory junction potentials (e.j.p.s) which gave rise to action potentials. Some cells from the mouse vas deferens showed similar e.j.p.s and action potentials, although the threshold for the initiation of action potentials was lower and more variable. 5. The majority of cells in the mouse vas deferens failed to show action potentials in response to a single stimuli even though the amplitude of e.j.p.s was from 35 to 40 mV. This was probably due to the large resting membrane potentials of these cells, as all-or-nothing action potentials could be evoked if successive e.j.p.s were allowed to sum with each other or if a depolarizing current pulse was applied at the peak of an e.j.p. 6. The nature of the response to nerve stimulation recorded from differnt cells in the mouse vas deferens could be correlated with the amplitude and time course of the response of the same cell to intracellular stimulation. 7. It is concluded that individual smooth muscle cells in both preparations are probably coupled electrically but that there are few, if any, low resistance pathways in the longitudinal direction in the mouse vas deferens.

Action Potentials↗
PubMed1977

Can nonadrenergic inhibitory varicosities be identified structurally.

The distribution of vesicles in axon varicosities was examined in rabbit jejunum and opossum esophagus. Circular muscle cells of both rabbit jejunum and opossum esophagus responded to stimulation of intrinsic nerves with inhibitory junction potential in nearly all cases. Inhibitory junction potentials were rare and small in longitudinal muscle cells of rabbit jejunum. There were few axon varicosities with a predominance of large opaque vesicles or large dense-cored vesicle in any muscle layer of rabbit or opossum or in the plexuses of rabbit jejunum. There were almost as high a proportion of such varicosities in longitudinal as in circular muscle of rabbit jejunum, and there were almost none in circular muscle of opossum esophagus. The distribution of vesicles in varicosities was found often to be heterogeneous and could account for the observed occurrence of a small proportion of varicosities with a predominance of large vesicles. It is suggested that there is no structural distinction in vertebrates between axons which are cholinergic and axons which are nonadrenergic inhibitory.

Animals↗
PubMed1975

The effects of calcium and magnesium on inhibitory junctional transmission in smooth muscle of guinea pig small intestine.

The membrane potential of smooth muscle cells in the circular layer of the guinea pig ileum was recorded using intracellular electrodes. Transmural stimulation, in the presence of atropine, caused a transient hyperpolarization, an inhibitory junction potential (IJP). IJP's are thought to result from the action of transmitter released from intramural inhibitory nerves. It has been reported that, in the guinea pig jejunum, the amplitude of the IJP resulting from field stimulation is not altered by changes in the calcium and magnesium ion concentration in the bathing solution. Experiments reported here have shown that the IJP amplitude decreased markedly on reducing the calcium ion concentration and or increasing the magnesium ion concentration. Indirect evidence is presented suggesting that the decrease in amplitude of the IJP is due to a decrease in the amount of transmitter released.

Animals↗
PubMed1975

Two descending nerve pathways activated by distension of guinea-pig small intestine.

1. Intracellular recordings were made from myenteric neurones of the guinea-pig small intestine in preparations which had a synaptic input from an orally situated segment of intestine. 2. Excitatory synaptic potentials could be evoked in most neurones by distension of the attached intestinal segment. 3. It was possible to distinguish two distinct firing patterns of synaptic potentials in response to distension. A transient short latency discharge was recorded from some neurones. From the others, a persistent synaptic discharge was recorded only after a long latency (2-11 sec). 4. Distension of intestinal segments evoked short latency transient inhibitory junction potentials in the circular muscle layer followed by excitatory junction potentials in both the circular and longitudinal muscle layers. 5. It is suggested that distension may cause both descending inhibition and, after a delay, descending excitation of the guinea-pig small intestine.

Animals↗
PubMed1973

Action of botulinum toxin on transmission from sympathetic nerves to the vas deferens.

Botulinum toxin (Type A) depressed or abolished transmission from postganglionic nerves to smooth muscle of isolated preparations of guinea-pig and mouse vas deferens. The time course of blockade was 2 to 6 times slower than that observed with the same concentration of the same batch of toxin on the rat diaphragm. Spontaneous excitatory junction potentials were still observed after 7 h exposure, indicating that the smooth muscle membrane was still able to respond to noradrenaline. Depression of transmission is probably due to a presynaptic action of unknown nature.

Action Potentials↗
PubMed1971

Excitatory input from the distal colon to the inferior mesenteric ganglion in the guinea-pig.

1. Intracellular recordings were obtained from ganglion cells in the guinea-pig inferior mesenteric ganglion (IMG) with a segment of the distal colon attached to the lumbar colonic nerves.2. Continuous electrical activity consisting of excitatory synaptic potentials and action potentials was recorded from ganglion cells in all regions of the IMG.3. The ;spontaneous' synaptic potentials were indistinguishable from those elicited by submaximal stimulation of any of the nerve trunks connected to the IMG.4. The excitatory activity was irreversibly abolished when the lumbar colonic nerves were cut and reversibly abolished when tetrodotoxin (5 x 10(-7) g/ml.) was added to the colon side of a two-compartment organ bath.5. Addition of dihydro-beta-erythroidine (5 x 10(-6) g/ml.) to the ganglion side of the bath abolished the synaptic activity of colonic origin and the synaptic responses to stimulation of any of the nerve trunks connected to the IMG.6. Addition of dihydro-beta-erythroidine (1 x 10(-5) g/ml.) to the colon side of the bath markedly depressed the synaptic input of colonic origin but had no effect on synaptic responses produced by preganglionic nerve stimulation.7. Distension of the colonic segment and the application of 5-HT (1 x 10(-5) g/ml.) to the mucosal surface of the colon increased the frequency of synaptic input.8. The synaptic input from the colon was transiently blocked following repetitive stimulation of any of the nerve trunks connected to the IMG. The discharge of miniature synaptic potentials was unaffected.9. Addition of noradrenaline (1 x 10(-7) to 1 x 10(-6) g/ml.) to the colon side of the bath reduced, and in some cases completely abolished, the synaptic input to the IMG. Phentolamine (1 x 10(-6) g/ml.), when added to the colon side of the bath, blocked the effect of noradrenaline and the transient inhibition following repetitive nerve stimulation.10. Addition of noradrenaline (1 x 10(-4) g/ml.) to the ganglion side of the bath reduced but never abolished the amplitude of the synaptic potentials of colonic origin.11. It was concluded that in the guinea-pig, the IMG is involved in a peripheral reflex whose afferent limit of this reflex consists of the axons of cholinergic neurones within the wall of the colon. Many of these neurones are driven either directly or indirectly by cholinergic synapses. The efferent noradrenergic neurones of the IMG function as a group of inhibitory neurones which depress the activity of the excitatory neurones of the colon which are driving them.

Action Potentials↗