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Biomedical subjects

G G Collins

Publications and source records attributed to G G Collins.

At least 55 records · Page 3Linked to original sources
PubMed1976

Indirect effects of amino-acids on sympathetic ganglion cells mediated through the release of gamma-aminobutyric acid from glial cells.

1 All experiments were performed on rat isolated desheathed superior cervical ganglia maintained in Krebs solution containing amino-oxyacetic acid (10 muM) at 25 degrees C. 2 Influx rates of gamma-amino-n-butyric acid (GABA) were measured by incubating ganglia in 0.5 muM [3H]-GABA for 30 minutes. Influx was inhibited by 50% on adding 14.3 muM unlabelled GABA, 59.2 muM beta-alanine (BALA) or 424 muM beta-amino-n-butyric acid (BABA). 3 Efflux of [3H]-GABA into non-radioactive solution superfused over ganglia previously incubated for 60 min in 1 muM [3H]-GABA was measured. The mean resting efflux rate coefficient (k) was 0.64 +/- 0.05 X 10(-3) min-1. Addition of high concentrations of unlabelled GABA, BABA or BALA to the superfusing solution increased k by (maximally) 3.6-4.3 times; half-maximal increases occurred at the following concentrations: GABA, 16 muM; BALA, 85 muM; BABA, 606 muM. Replacement of external Na+ with Li+ or TRIS increased the resting value of k and inhibited acceleration by external amino acids. Prior incubation in 1 muM [3H]-GABA with 1 mM unlabelled GABA increased resting k 1.5 times, but did not alter the peak rate coefficient produced by external amino acids. 4 Neuronal depolarization produced by the amino acids was measured with surface electrodes. Pre-incubation in 1 mM GABA for 60 min potentiated low-amplitude responses to BALA or BABA but not those to GABA or 3-aminopropanesulphonic acid (a potent agonist with low affinity for the GABA carrier). Omission of external Na+ reduced responses to BABA but increased those to GABA. 5 Incubation in 1 mM GABA for 60 min (as required to potentiate BABA or BALA actions) increased the amount of GABA in the tissue from 0.21 to 0.73 mmol/kg wet weight. Autoradiographs in which labelled GABA was used indicated that uptake into neuroglial cells was responsible for this accumulation. 6 It is suggested that: (i) BALA and BABA are substrates for the inward GABA carrier responsible for GABA entry into ganglionic glial cells; (ii) they accelerate efflux by inhibiting carrier-mediated reaccumulation of effluent GABA by the glial cells; (iii) interstitial GABA concentrations are thereby increased to a level capable of depolarizing adjacent neurones; and (iv) this, rather than direct GABA-receptor activation, accounts for the depolarization produced by low concentrations of BALA and BABA. Potentiation of their depolarizing action after pre-incubation in 1 mM GABA is suggested to result from the increased amount of intracellular GABA available for release, and is quantitatively compatible with this increase; inhibition in Na+-free solution is due to their inability to inhibit reaccumulation of GABA under these conditions. 7 A model for the action of carrier substrates is described in an Appendix. Calculations based thereon yield increments in interstitial GABA concentration in the presence of carrier substrates compatible with those determined experimentally (up to 1 muM at rest or 3.4 muM after pre-incubation in GABA).

Amino Acids↗
PubMed1976

The release of endogenous amino acids from the rat visual cortex.

The release of endogenous taurine, GABA, glycine, aspartate, glutamate, glutamine and alanine from the rat visual cortex was measured using a cortical cup technique. The electrocorticogram (ECoG) was monitored throughout most experiments. 2. Spreading depression, evoked by the dropwise placement of 10% KCl solution on to the brain outside the cup was associated with a significant increase in the release of GABA and glutamine but a marked fall in that of glutamate. The evoked release of GABA and glutamate but not of glutamine was Ca2+ dependent. 3. A solution containing 50 mM-K+ placed within the cup elicited a significant increase in the release of taurine and GABA, whereas 100 mM-K+ additionally released aspartate and glutamate. The K+-evoked release of these amino acids with the exceptions of taurine and glutamine was Ca2+-dependent. 4. Three series of experiments were carried out in which the preparations were stimulated electrically. Bipolar stimulation (100 Hz, 1 msec pulse width, 2-5 mA for 5 min) with the electrode within the cup was followed by significant increases in taurine, GABA and glutamate release; using a 5 mA current, there was an additional release of aspartate and alanine. Only the evoked release of GABA and glutamate was Ca2+ dependent. 5. In the second and third series of experiments, the electrode was sited adjacent to the cup or on the contralateral cortex respectively. Following stimulation (100 Hz, 1 msec pulse width, 2-5 mA for 5 min) there was a significant increase in taurine and GABA release and a significant fall in the release of aspartate and glutamate. With the exception of taurine, these changes in release were Ca2+ dependent. Reducing the stimulus current to 1-5 mA or the period of stimulation to 2-5 min initiated similar but statistically insignificant changes in release. A range (10-100 Hz) of stimulation frequencies was examined: the evoked release of GABA was linearly related to frequency whereas that of taurine was frequency-independent. The fall in aspartate and glutamate release was maximal at a frequency of about 50 Hz. 6. The results are discussed in relation to (a) the possible sites of release of the amino acids and (b) the proposed neurotransmitter roles of the physiologically active amino acids.

Alanine↗
PubMed1972

The levels of soluble nucleotides in wheat aleurone tissue.

The content of soluble nucleotides in aleurone layers isolated from mature wheat (Triticum aestivum var. Olympic) grain was investigated. The most abundant nucleotides were adenosine triphosphate, uridine triphosphate, and uridine diphosphoglucose. Smaller amounts of guanosine triphosphate, cytidine triphosphate, adenosine diphosphate, and nicotinamide adenine dinucleotide were also identified. The levels of some of these nucleotides were increased after incubation of the tissue under certain conditions.Nucleotide levels were measured at intervals during incubation of aleurone layers in water. The changes observed are discussed in relation to a response by the tissue to wounding.

Journal Article↗
PubMed1972

The metabolism of soluble nucleotides in wheat aleurone layers treated with gibberellic Acid.

The metabolism of soluble nucleotides was investigated in wheat (Triticum aestivum var. Olympic) aleurone layers treated with gibberellic acid. Whereas nucleotide levels were relatively unaffected by the treatment, a transient increase was observed in the incorporation of (32)P. The effect was maximal 30 to 60 minutes after gibberellic acid was administered, and by 180 minutes incorporation was lower than in the control. The greatest changes were detected in the nucleoside triphosphates, particularly in cytidine triphosphate. The findings are discussed in relation to the mode of action of gibberellic acid.

Journal Article↗