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| Content Provider | World Health Organization (WHO)-Global Index Medicus |
|---|---|
| Author | Maggi, C. A. Giuliani, S. Santicioli, P. Brading, A. F. |
| Description | Author Affiliation: Maggi CA ( Pharmacology Department, A. Menarini Pharmaceuticals, Florence, Italy.) |
| Abstract | 1. The aim of this study was to assess the role of sarcoplasmic reticulum (SR) calcium (Ca2+) in the smooth muscle relaxant and hyperpolarizing actions of calcitonin gene-related peptide (CGRP) in the guinea-pig ureter. 2. CGRP (0.1 microM) rapidly and transiently reduced myogenic phasic contractions (twitches) produced by electrical field stimulation (EFS). Approximately 70% of the response to CGRP was antagonized by glibenclamide (1 microM). 3. Cyclopiazonic acid (CPA, 10 microM), ryanodine (100 microM) and thapsigargin (1 microM) reduced only the glibenclamide-sensitive component of the response to CGRP (0.1 microM) but did not modify the mechano-inhibitory effect of cromakalim (3 microM). A low concentration of CPA (1 microM), assumed to produce a limited impairment of Ca2+ uptake from the stores, prolonged the duration of the inhibitory response to CGRP. Pre-exposure to caffeine (5 mM) inhibited the suppression of twitches by CGRP or cromakalim. 4. When the frequency of EFS was increased, the suppression of twitches by CGRP was reduced. Under these conditions, CPA (1 microM) again prolonged the duration of the inhibitory response to CGRP. 5. CGRP (0.1 microM) and cromakalim (3 microM) markedly depressed the phasic component of contractions to 80 mM KCl. CPA (10 microM) antagonized the inhibitory effect of CGRP but not that of cromakalim. Inhibition of the tonic contraction to 80 mM KCl by CGRP was insensitive to CPA. 6. In sucrose gap experiments, a 5 min exposure to CGRP (0.1 microM) or cromakalim (3 microM) produced a sustained membrane hyperpolarization. Caffeine (5 mM) produced a glibenclamide-sensitive transient hyperpolarization followed by a sustained depolarization. When tested in a Ca(2+)-free medium the hyperpolarization produced by CGRP, cromakalim or caffeine was reduced. In normal Krebs, pre-exposure to CPA (10 microM, 60 min) only abolished the hyperpolarization induced by CGRP. In contrast, 5 min after a caffeine challenge (5 mM) the hyperpolarizations induced by CGRP or cromakalim were reduced. The CGRP-induced hyperpolarization was insensitive to apamin (0.1 microM) or charybdotoxin (0.1 microM). 7. We conclude that the K channel-opening action of CGRP in the guinea-pig ureter requires the mobilization of intracellular Ca2+ from a caffeine- and CPA-sensitive store, leading to transient activation of glibenclamide-sensitive K channels. The K channel-opening action of caffeine appears to involve Ca2+ mobilization from a store which is insensitive to depletion by CPA. |
| ISSN | 00071188 |
| e-ISSN | 14765381 |
| Journal | British Journal of Pharmacology |
| Issue Number | 6 |
| Volume Number | 118 |
| Language | English |
| Publisher | Wiley Online Library(on behalf of The British Pharmacological Society) |
| Publisher Date | 1996-07-01 |
| Publisher Place | Great Britain (UK) |
| Access Restriction | Open |
| Subject Keyword | Calcitonin Gene-Related Peptide Pharmacology Calcium Physiology Muscle, Smooth Metabolism Potassium Channels Drug Effects Ureter Animals Caffeine Calcium-Transporting ATPases Antagonists & Inhibitors Electric Stimulation Enzyme Inhibitors Glyburide Guinea Pigs Hypoglycemic Agents In Vitro Techniques Indoles Membrane Potentials Muscle Contraction Phosphodiesterase Inhibitors Ryanodine Sarcoplasmic Reticulum Thapsigargin |
| Content Type | Text |
| Resource Type | Article |
| Subject | Pharmacology |
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