Characterization of intestinal smooth muscle responses and binding sites for endothelin
| Autor: | Francine Liard, Michel Garneau, Jorge Jaramillo, Gordon Bolger |
|---|---|
| Rok vydání: | 1992 |
| Předmět: |
Male
medicine.medical_specialty Carbachol Physiology Guinea Pigs Psychotomimetic drug chemistry.chemical_element Receptors Cell Surface In Vitro Techniques Calcium Iodine Radioisotopes chemistry.chemical_compound Nifedipine Physiology (medical) Internal medicine Homologous desensitization medicine Animals Intestinal Mucosa Pharmacology Receptors Endothelin Chemistry Endothelins Calcium channel Muscle Smooth General Medicine Endocrinology Calcium Channels Endothelin receptor Histamine Muscle Contraction medicine.drug |
| Zdroj: | Canadian Journal of Physiology and Pharmacology. 70:377-384 |
| ISSN: | 1205-7541 0008-4212 |
| DOI: | 10.1139/y92-047 |
| Popis: | The contractile activity of and binding sites for endothelin-1 (ET-1) were investigated in isolated guinea-pig ileal longitudinal smooth muscle (GPILM). ET-1 produced concentration-dependent contractions of GPILM that either slowly subsided in the continued presence of ET-1 or rapidly subsided following washing of the tissue. The ED50 value for ET-1 contractions was 4.2 ± 1.3 × 10−9 M. The removal of extracellular calcium or pretreatment with nifedipine produced a complete inhibition of the contractions to ET-1. The IC50 value of nifedipine for inhibition of ET-1 mediated contractions was 3.0 ± 0.8 × 10−8 M. ET-1 produced a marked prolonged homologous desensitization of its contractile response but did not affect the responses mediated by carbachol, histamine, serotonin, substance P, and PLA2. High-affinity binding sites for 125I-labelled ET-1 were identified on microsomal membranes prepared from GPILM with Kd and Bmax values obtained by Scatchard analysis of 3.5 ± 0.6 × 10−10 M and 2138 ± 159 fmol/mg protein, respectively. The binding of 125I-labelled ET-1 to GPILM microsomes was characterized by a rapid association (kob value of 0.077 min−1 at a radioligand concentration of 0.45 nM and an extremely slow dissociation (kl value of 0.011 min−1; t1/2 value of 793 min). The binding was unaffected by the calcium channel antagonists nifedipine, verapamil, and diltiazem (10−6 M); the receptor antagonists phenoxybenzamine, atropine, and naloxone (10−6 M) and propranolol; and the peripheral benzodiazepine receptor antagonists Ro 5-4864 and PK 11195 and psychotomimetic drug phencyclidine (10−5 M). Incubation of GPILM with ET-1 (2 × 10−8 M) for 10 min followed by washing of the tissue for 1 h resulted in a significant (p 125I-labelled ET-1 binding that partially recovered following 2 h of washing the tissue. These results demonstrate that ET-1 is an intestinal smooth muscle spasmogen that produces its pharmacologic effects by a mechanism(s) that is not shared by other major intestinal neurotransmitters. Furthermore, intestinal smooth muscle contains specific high-affinity binding sites that likely mediate the contractile responses to ET-1.Key words: intestine, smooth muscle, endothelin, calcium channels, contraction. |
| Databáze: | OpenAIRE |
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