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Biomedical subjects

H Imamura

Publications and source records attributed to H Imamura.

At least 397 records · Page 22Linked to original sources
PubMed1977

Beta-adrenoceptor blocking and electrophysiological effects of bufetolol in the guinea pig atria.

The potency of blockade of bufetolol, a beta-adrenoceptor blocking drug, and effects of bufetolol on the action potential, contractile force and various electrophysiological properties of the atrium were investigated in comparison with propranolol and quinidine. Bufetolol had a pA2 of 8.65 against the positive chronotropic action of isoproternol on the guinea pig sinus node. Bufetolol, 10(-7) g/ml, did not affect the action potential of the atrial muscle, while the drug, 3 X 10(-5) g/ml, significantly decreased the overshoot potential, the amplitude and the maximum rate of rise of the action potential and prolonged the times for 50% and 90% repolarization. The contractile force was reduced by bufetol, 3 X 10(-5) g/ml. The maximum responsive frequency to the driving stimulus was decreased by bufetol, 3 X 10(-5) g/ml. The excitability of the muscle membrane was suppressed by bufetolo, 3 X 10(-5) g/ml, as indicated by changes in membrane responsiveness, membrane reactivation and strength-duration curve. Propranolol, 10(-5) g/ml and quinidine, 10(-5) g/ml showed similar effects on excitability. The authors suggest that these effects of bufetolol are responsible for its antidyshythmic effects.

Action Potentials↗
PubMed1977

[Simple on-line digital determination of the cardiac action potential and its application].

A system of digital measuring of the cardiac action potential was constructed in order to measure quickly and accurately the resting potential or maximum diastolic potential, overshoot potential, amplitude, time for 50% repolarization and time for 90% repolarization. This system consists of a dual-beam oscilloscope, a digital voltage meter, a digital interval meter and a simple circuit constructed by operational amplifiers. The measurement of the action potential was achieved by tracing only the resting potential or the maximum diastolic potential and the crest of the action potential on the oscilloscope using another beam. The time for measurement is usually 10-15 sec and errors in measurement were considered to be negligible. This system is considered to be useful for digital measurement of the action potential of various cardiac tissues. This system was applied for observation of effects of bufetolol, an adrenergic beta-receptor blocking drug on the action potential of the dog Purkinje fibres. Bufetolol (10(-5) M) caused a slight depolarization of the maximum diastolic potential, decreased overshoot potential, amplitude and maximum rate of rise, and shortened the time for 50% repolarization of the action potential. Bufetolol (10(-4) M) additionally prolonged the time for 90% repolarization.

Action Potentials↗
PubMed1977

Facilitatory and inhibitory effects of gamma-aminobutyric acid on ganglionic transmission in the sympathetic cardiac nerves of the dog.

Effects of gamma-aminobutyric acid (GABA) on ganglionic transmission in the peripheral course of the sympathetic cardiac nerves were investigated in vagotomized and cardiac decentralized open-chest dogs. GABA (1-300 microgram/kg) was given i.v. during electrical stimulation of pre-or postganglionic fibers which induced a sustained acceleration of sinus rate. GABA in small doses of 1 and 3 microgram/kg augmented the sinus acceleration during electrical stimulation of the ansa subclavia which largely consists of preganglionic fibers, but depressed the sinus acceleration in large doses over 30 microgram/kg. With a dose of a 10 microgram/kg, its effect was dual and varied from preparation to preparation. On the other hand, GABA did not modify basal heart rate or the increase in heart rate in response to stimulation of the stellate cardiac nerve postganglionic fibers. These results clearly demonstrated dual effects of GABA on ganglionic transmission, i.e., facilitation in small doses and depression in large doses. The depression caused by large doses of GABA was markedly reduced by picrotoxin, 1 mg/kg, while the facilitation remained unaffected. Treatment with atropine, 1 mg/kg, and phenozy-benzamine, 1 mg/kg, failed to influence the effects of GABA. The possible mechanisms for these effects of GABA are discussed.

Aminobutyrates↗