title: Potassium-induced contraction in the lamb proximal urethra: involvement of norepinephrine and different calcium entry pathways.
abstract: The purpose of this work was to investigate the mechanisms involved in the peculiar biphasic response of the lamb urethral smooth muscle to high K+ solutions. The relative amplitude of the phasic and tonic components of the contraction and its reproducibility were dependent on the concentration of K+ used. Only concentrations higher than 80 mM (i.e., 120 mM) showed a tonic component greater in amplitude than the phasic one and manifested a tachyphylactic effect. Phentolamine (10(-6) M), prazosin (10(-6) M) and chemical denervation with 6-hydroxydopamine significantly inhibited the tonic component of the K+ (120 mM)-induced contraction, modifying its morphology. Reproducible contractions to K+ (120 mM) could be obtained in the presence of prazosin (10(-6) M) or cocaine (10(-6) M). The preparations were also shown to accumulate [3H]noradrenaline and release it upon depolarization with K+ (60 and 120 mM). Calcium removal inhibited the K+ (120 mM)-induced contraction. After addition of calcium (0.5-5 mM) the contractile activity was restored. Nifedipine (10(-6) M) and verapamil (10(-6) M) but not sodium nitroprusside (10(-6) M) significantly blocked the contractile response for calcium as well as the phasic component of the K+ contraction in calcium-containing medium. In preparations treated with prazosin (10(-6) M) the tonic component of the K+ (120 mM) contraction was more sensitive to nifedipine and removal of extracellular calcium than the phasic one.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Departamento de Fisiología Animal, Facultad de Veterinaria, Universidad Complutense de Madrid, Spain.
authors.forename: A
authors.initials: A
authors.lastname: García-Pascual
authors.forename: G
authors.initials: G
authors.lastname: Costa
authors.forename: M
authors.initials: M
authors.lastname: Isla
authors.forename: E
authors.initials: E
authors.lastname: Jimenez
authors.forename: A
authors.initials: A
authors.lastname: García-Sacristán
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism / Q000502:physiology*; D003042:Cocaine / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D009638:Norepinephrine / Q000378:metabolism / Q000502:physiology*; D012601:Scopolamine / Q000494:pharmacology; D012756:Sheep; D013268:Stimulation, Chemical; D014316:Tritium; D014521:Urethra / Q000187:drug effects* / Q000502:physiology
chemical_list: D000317:Adrenergic alpha-Antagonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D014316:Tritium; D001285:Atropine; D012601:Scopolamine; D003042:Cocaine; D009638:Norepinephrine