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J D Huizinga

Publications and source records attributed to J D Huizinga.

113 records · Page 7Linked to original sources
PubMed1980

Inhibition of fundic strips from guinea-pig stomach: the effect of theophylline on responses to adenosine, ATP and intramural nerve stimulation.

The effect of theophylline on the ATP response, the adenosine response and the inhibitory junction potential was studied on circular smooth muscle preparations of the guinea-pig stomach. The amplitude of the inhibitory junction potential evoked after stimulation of the non-cholinergic, non-adrenergic nervous system was not affected by a moderate concentration of theophylline (5 x 10(-6)-10(-5) M). At higher concentrations (5 x 10(-5)-10(-3) M) theophylline relaxed the muscle hyperpolarized the cell membrane and reduced the inhibitory junction potential slightly. ATP and adenosine (5 x 10(-6)-10(-3) M) also caused relaxation of the smooth muscle cells and hyperpolarization of the cell membrane. Theophylline (5 x 10(-6)-10(-3) M) did not antagonize these effects; in the presence of theophylline (5 x 10(-5)-10(-3) M) additional relaxations produced by ATP and adenosine were limited in view of the muscle tone. These results indicate that theophylline does not inhibit either the effect of the non-adrenergic inhibitory transmitter on the smooth muscle cells of the guinea-pig stomach or the actions of ATP and adenosine. This suggests that the existence of theophylline-sensitive adenosine receptors in the stomach-muscle cell membrane is unlikely and that theophylline is not the drug of choice to support the purinergic nerve hypothesis.

Adenosine↗
PubMed1979

Inhibition of fundic strips from guinea-pig stomach: the effect of theophylline on the membrane potential, muscle contraction and ion fluxes.

The effect of theophylline on the smooth muscle cells of the fundic part of the stomach of the guinea pig was investigated. Theophylline hyperpolarized the membrane, inhibited spike discharges and slow waves and produced relaxation of the muscle cells. Furthermore, the theophylline-induced relaxation was not affected in low sodium solution or during inhibition of the sodium pump. Partial inhibition of the theophylline relaxation was seen in muscle depolarized by a high potassium solution and also when ATP was the relaxant. The potassium efflux was enhanced by ATP, but was not markedly changed by theophylline. A change in calcium efflux in the presence of theophylline could not be measured in quiescent preparations. The calcium influx was not changed by theophylline in Krebs, by low Ca, or by high K solution. Furthermore, the tissue content of cyclic AMP was increased by 59.6% in the presence of theophylline (2 x 10(-3) M). The conclusion is reached that the most likely mode of action of theophylline is a suppression of spontaneous activity and an extensive calcium binding to internal sites.

Animals↗
PubMed1979

The effect of enkephalins on the intramural inhibitory non-adrenergic nerve responses of smooth muscle.

The study concerned the effect of enkephalins and naloxone on the inhibitory non-adrenergic nerve responses of the taenia coli and the stomach smooth muscle cells of the guinea pig. Met-enkephalin, leu-enkephalin and D-ala-enkephalin (10(-8)10(-5)M) did not affect the muscle tension or membrane potential measured simultaneously using the sucrose-gap method. Naloxone (5x10(-8)--5x10(-6)M) relaxed the stomach strip, but did not modify the inhibitory junction potential. These results indicate that enkephalins are not involved in the nonadrenergic inhibitory nervous system, except possibly as neuromodulators at an interneuronal synaptic level.

Animals↗