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| Content Provider | World Health Organization (WHO)-Global Index Medicus |
|---|---|
| Author | Uyama, Y. Imaizumi, Y. Watanabe, M. |
| Description | Author Affiliation: Uyama Y ( Department Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University, Japan.) |
| Abstract | 1. Effects of cyclopiazonic acid (CPA), a specific inhibitor of Ca(2+)-ATPase in endo- and sarcoplasmic reticulum (ER/SR), on contractile responses, cytosolic Ca2+ concentration and spontaneous electrical activity were examined in ileal longitudinal smooth muscle strips. 2. After intracellular stored Ca2+ in intact ileal strips was depleted by application of 25 mM caffeine in Ca(2+)-free solution, Ca(2+)-loading was performed in the absence or presence of 10 microns CPA in a standard solution containing 2.2 mM Ca2+. Subsequent application of caffeine in Ca(2+)-free solution induced a phasic contraction which was significantly smaller in the strip pretreated with CPA than that in the control. 3. Spontaneous and 20 mM K(+)-induced contractions in the presence of 1 microM atropine were markedly enhanced by 1-30 microM CPA, whereas that induced by 80 mM K+ was not. The magnitude of repetitive transient elevation of cytosolic Ca2+ concentration ([Ca2+])i) and concomitant phasic contractions were markedly enhanced by CPA. The effects were abolished by 10 microM verapamil and restored by 10 microM Bay K 8644. 4. Application of 10 microM CPA depolarized the cell by about 5 mV, decreased the action potential (AP) afterhyperpolarization and markedly increased the frequency of spontaneous AP. These effects were mimicked by 100 nM charybdotoxin. 5. The rate of decay of [Ca2+]i and tension after the bathing solution was changed from one containing 140 mM K+ and 2.2 mM Ca2+ to one containing 5.9 mM K+ and 0 mM Ca2+ was significantly slowed when 10 microM CPA was added to the latter solution. 6. These results indicate that CPA enhances ileal smooth muscle excitability and increases Ca2+-influx through voltage-dependent Ca2+ channels. The effect may be consistent with the hypothesis that CPA-induced decrease in stored Ca due to Ca-pump inhibition reduces the Ca2+-dependent K+ current and indirectly enhances Ca2+-influx through membrane activity resulting from the increased excitability.Direct evidence for the regulation of Ca2+ channel activity by intracellular Ca storage sites was not obtained in the present study. |
| ISSN | 00071188 |
| e-ISSN | 14765381 |
| Journal | British Journal of Pharmacology |
| Issue Number | 2 |
| Volume Number | 110 |
| Language | English |
| Publisher | Wiley Online Library(on behalf of The British Pharmacological Society) |
| Publisher Date | 1993-10-01 |
| Publisher Place | Great Britain (UK) |
| Access Restriction | Open |
| Subject Keyword | Calcium-Transporting ATPases Antagonists & Inhibitors Indoles Pharmacology Muscle, Smooth Drug Effects Sarcoplasmic Reticulum Enzymology Animals Atropine Caffeine Calcium Metabolism Cytosol Electrophysiology Guinea Pigs Ileum In Vitro Techniques Membrane Potentials Muscle Contraction Nerve Fibers Potassium Research Support, Non-U.S. Gov't |
| Content Type | Text |
| Resource Type | Article |
| Subject | Pharmacology |
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