Search PubMed⌕ Search

Biomedical subjects

T Forrester

Publications and source records attributed to T Forrester.

99 records · Page 6Linked to original sources
PubMed1970

An electrophysiological investigation of the slow fibre system in the frog rectus abdominis muscle.

1. Junctional potentials were recorded with a micro-electrode inserted into muscle fibres of the rectus abdominis muscle of the frog. Large and small nerve fibres were stimulated separately, using a selective stimulation technique. In a few muscle fibres rectangular current pulses were applied through a second micro-electrode to examine current-voltage relations.2. Two groups of muscle fibres could be distinguished: (a) Muscle fibres with resting potentials less negative than -75 mV, being localized at the ventral surface only and representing about 9% of the superficial fibres. These fibres were found to be innervated by small (high-threshold) nerve fibres and responded to single indirect stimuli with a typical s.j.p. (long latency, multiple components, after-hyperpolarization); upon repetitive stimulation summation of s.j.p.s and a slowly increasing tension could be recorded. The fibres showed a slow time course of electrotonic potentials, relatively high membrane resistance and ;delayed rectification'. (b) Muscle fibres with generally much higher resting potentials, being innervated by large (low-threshold) nerve fibres only. Upon indirect stimulation a short-latency end-plate or action potential (followed by a twitch) was recorded. The membrane time constant and input resistance of these fibres were similar to those of twitch fibres in other frog muscles.3. No evidence was found in the present work for the existence of an intermediate type of muscle fibre.4. It is concluded that the rectus muscle, similar to other frog muscles, contains two distinct types of muscle fibres, twitch and slow.

Abdomen↗
PubMed1969

Identification of adenosine triphosphate in human plasma and the concentration in the venous effluent of forearm muscles before, during and after sustained contractions.

1. When diluted human plasma is perfused through a frog heart, a marked augmentation of the heartbeat is produced which is very similar in action to that of low concentrations of adenosine triphosphate (ATP) on the heart.2. It was established that the substance in the plasma responsible for the heart stimulation was ATP. The following tests were used: (a) the diluted plasma emitted light from firefly lantern extract characteristic of the light signal produced by a solution of ATP; (b) the stimulatory effect on the frog heart and luminescent effect upon the firefly extract were abolished by incubation of the plasma solution with the enzyme apyrase, which converts ATP to adenosine monophosphate (AMP); AMP does not stimulate the heart or cause light to be emitted from firefly extract; (c) the stimulatory substance in the plasma was eluted through a column of Sephadex G-25 in the same pattern as ATP; and (d) simultaneous assay of plasma solutions on frog heart and firefly extract produced the same quantitative result as that produced by a solution of ATP.3. The amount of ATP in plasma from the venous blood of resting subjects ranged from 0.19 to 0.95 mug/ml. (mean 0.63 mug/ml., S.D. +/- 0.25); up to half of the ATP detected could be attributed to blood platelet damage. Simultaneous arterial and venous samples of blood from four subjects at rest had mean concentrations of 0.19 mug/ml. (0.07-0.26 mug/ml.) and 0.70 mug/ml. (0.57-0.84 mug/ml.) respectively.4. The concentration of ATP in the venous effluent from exercising forearm muscles was measured. The venous concentration consistently increased over the resting values in response to exercise while in one subject little change occurred in the arterial blood concentration during the exercise. It was concluded that the ATP was added to the blood in its passage through the muscle bed.5. The origin of the ATP, including erythrocytes, blood platelets and active skeletal muscle, is discussed.

Adenine Nucleotides↗
PubMed1968

The release of adenosine triphosphate from frog skeletal muscle in vitro.

1. Active frog sartorius muscle in vitro liberates a substance into the bathing solution which has a pronounced stimulatory action on the frog heart.2. The stimulatory effect is not due to an increase in the K(+) concentration of the bathing solution, nor is it due to the liberation of catecholamines.3. In a molecular sieve chromatography procedure the stimulatory substance can be eluted in a single fraction which shows a maximum absorption of U.V. light at a wave-length of 265 nm, indicative of the presence of substances containing a purine ring.4. Low concentrations (10(-7)-10(-8) g/ml.) of adenosine triphosphate (ATP), adenosine diphosphate (ADP) and uridine triphosphate (UTP) have a marked stimulatory action on the frog heart. The action of ATP and ADP on the heart is qualitatively very similar to that of the muscle bathing solution, while the action of UTP is distinctly different. The triphosphates of inosine, cytidine and guanosine stimulate the heart when in high concentration only. Adenosine and adenosine monophosphate do not stimulate the heart.5. Incubation of the muscle bathing solution and of solutions of ATP with the enzyme apyrase for the same time produces a similar marked reduction in the stimulatory action of both on the heart. Apyrase catalyses the break-down of nucleotide triphosphates to monophosphates.6. The elution behaviour of the stimulatory substance determined by molecular sieve chromatography is the same as that for ATP.7. The muscle bathing solution causes light to be emitted from firefly lantern extract, the pattern of light emission being similar to that produced by nucleotide triphosphates.8. The concentrations of ATP having the same quantitative action on the frog heart and on firefly extract as a given muscle bathing solution are almost identical, whereas the matching concentrations of ADP and UTP in the two methods of assay are widely different.9. It is concluded that ATP is released from active frog skeletal muscle in vitro. This release may play an important part in the reactive hyperaemia of muscular exercise since ATP has a powerful vasodilator action.

Adenosine Triphosphate↗