Drugs online research references
J Gen Physiol. 1990 Jan;95(1):1-27.
Internal and external effects of dihydropyridines in the calcium channel of skeletal muscle.
Valdivia HH, Coronado R.
Department of Physiology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas 77030.
The agonist effect of the dihydropyridine (DHP) (-)Bay K 8644 and the inhibitory effects of nine antagonist DHPs were studied at a constant membrane potential of 0 mV in Ca channels of skeletal muscle transverse tubules incorporated into planar lipid bilayers. Four phenylalkylamines (verapamil, D600, D575, and D890) and d-cis-diltiazem were also tested. In Ca channels activated by 1 microM Bay K 8644, the antagonists nifedipine, nitrendipine, PN200-110, nimodipine, and pure enantiomer antagonists (+)nimodipine, (-)nimodipine, (+)Bay K 8644, inhibited activity in the concentration range of 10 nM to 10 microM. Effective doses (ED50) were 2 to 10 times higher when HDPs were added to the internal side than when added to the external side. This sidedness arises from different structure-activity relationships for DHPs on both sides of the Ca channel since the ranking potency of DHPs is PN200-110 greater than (-)nimodipine greater than nifedipine approximately S207-180 on the external side while PN200-110 greater than S207-180 greater than nifedipine approximately (-)nimodipine on the internal side. A comparison of ED50's for inhibition of single channels by DHPs added to the external side and ED50's for displacement of [3H]PN200-110 bound to the DHP receptor, revealed a good quantitative agreement. However, internal ED50's of channels were consistently higher than radioligand binding affinities by up to two orders of magnitude. Evidently, Ca channels of skeletal muscle are functionally coupled to two DHP receptor sites on opposite sides of the membrane.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2153750&dopt=Abstract
Nippon Yakurigaku Zasshi. 1986 Sep;88(3):179-87.
[Electrophysiological effects of KW-3049, a new dihydropyridine type Ca antagonist, on isolated rabbit hearts, sinus nodal tissues and guinea-pig ventricular muscles]
[Article in Japanese]
Yoshitake I, Kubo K, Ikeda N, Kodama I, Toyama J, Yamada K.
Effects of KW-3049 on electrophysiological properties of the heart were examined using Langendorff-perfused hearts and superfused sinus nodal tissues of rabbits and superfused guinea-pig ventricular muscles. In rabbit hearts, KW-3049 at concentrations above 10(-7) M caused a dose-related prolongation of atrio-His bundle conduction time (AH), whereas His bundle-ventricular conduction time (HV) was unaffected. In spontaneously firing rabbit sinus nodal tissues, KW-3049 at concentrations above 10(-8) M prolonged cycle length significantly. At 10(-6) M, amplitude and the maximum upstroke velocity of sinus nodal action potential were decreased as well. In normally polarized guinea-pig ventricular muscles under 4 mM [K+]0, KW-3049 at concentrations above 10(-6) M shortened the action potential duration without affecting the resting membrane potential and the maximum upstroke velocity of action potential (Vmax). The Vmax of slow action potentials induced by isoproterenol at 10(-7) M was inhibited significantly by additional application of KW-3049 at concentrations above 10(-9) M. At above 10(-8) M, the amplitude and duration of slow action potentials were reduced significantly. The potency of this slow action potential inhibition by KW-3049 was slightly less than that of nifedipine, while it was 10 to 100 times greater than that of verapamil. Spontaneous activity of ventricular muscles induced by BaCl2 at 1 mM was abolished completely at 16 min after application of KW-3049 at 10(-7) M. These results suggest that KW-3049 may have a potent and selective inhibitory action on cardiac slow calcium channels.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2431981&dopt=Abstract
Nippon Sanka Fujinka Gakkai Zasshi. 1987 Oct;39(10):1723-8.
[Basic studies of the effects of various kinds of tocolytics on uterine contraction in pregnant rats]
[Article in Japanese]
Chimura T.
Department of Obstetrics and Gynecology, Yamagata University School of Medicine.
The effects of various substances involved in the inhibition of uterine contraction on the uterine muscle of pregnant rats were studied in vitro in terms of uterine contraction and alterations in cyclic nucleotides. 1) The inhibitory effect of 4-aminoantipyrine (4AA) on uterine contraction showed a pattern of decline, being less potent that tranylcypromine. The effect of nifedipine was the most potent, followed by ritodrine, tranylcypromine, RU 486 and 4AA, in that order. The inhibitory effects were diminished by administration of ONO-802.PGF2 alpha. 2) Cyclic nucleotide levels changed according to the potency of each agent in the process of inhibition. Although the level of c-AMP tended to increase and that of c-GMP tended to decrease, there were no changes in their levels when nifedipine was administered. 3) Blood and uterine muscle levels of c-AMP were increased in pregnant rats that had been given ritodrine prior to hysterectomy, and there was no inhibitory effect of ritodrine in comparison with pregnant rats that had not been given the agent. The pregnant rats that had been given ritodrine prior to hysterectomy also showed no significant change in the level of c-AMP in the bath-medium.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3429972&dopt=Abstract
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