Navegando por Palavras-chave "tetrodotoxin"

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    Different pathways for Ca2+ mobilization by angiotensin II and carbachol in the circular muscle of the guinea-pig ileum
    (Elsevier B.V., 1999-02-12) Shimuta, S. I.; Borges, ACR; Prioste, R. N.; Paiva, T. B.; Universidade Federal de São Paulo (UNIFESP)
    Ca2+ pathways activated by angiotensin II and carbachol were evaluated in the circular muscle of the guinea-pig ileum by recording mechanical and electrical activities. Transient contractions induced by angiotensin II were greatly reduced by Ca2+ removal from the medium whereas carbachol-induced responses were not significantly altered. Nifedipine had no effect on the responses to both agonists. A high concentration of tetrodotoxin (0.1 mu M) inhibited angiotensin II-induced contractile responses without affecting the depolarization, whereas 1 mM Ni2+ inhibited the mechanical and electrical effects. Neither tetrodotoxin nor Ni2+ affected carbachol-induced effects. These results indicate that angiotensin II-induced phasic contractions depend on extracellular Ca2+ but not on voltage-dependent L-type Ca2+ channels. It is suggested that angiotensin II activates Ni2+-sensitive Na+ and non-specific cationic channels, whereas the responses to carbachol are dependent on receptor-activated Ca2+ release. Furthermore the different response of the longitudinal and circular muscles to the inhibitory effects of tetrodotoxin and Ni2+ on the angiotensin II- and carbachol-induced contractions indicates that these agonists exert their own myogenic effects on each layer and are able to trigger different Ca2+ mobilization pathways. (C) 1999 Elsevier Science B.V. All rights reserved.