Characterization of alpha2-adrenoceptors in smooth muscles of the spontaneously hypertensive rat aorta.
Previous works have shown that the alpha(2)-adrenoceptor agonist UK 14,304 induced the relaxation and hyperpolarization of the rat aorta, mediated by alpha(2)-adrenoceptors present in the smooth muscles, through small-conductance, ATP-sensitive K(+) channels. We now report that in spontaneously hypertensive rat (SHR) aortic rings, UK 14,304 induced concentration-dependent hyperpolarizing responses, which were inhibited by yohimbine, an alpha(2)-adrenoceptor inhibitor, and by glibenclamide, a specific inhibitor of small-conductance, ATP-sensitive K(+) channels. The responses were also partially inhibited by iberiotoxin and by apamin. Treatment with N(omega)-nitro-L-arginine (L-NNA) did not affect the response to UK 14,304. These results indicate that alpha(2)-adrenoceptors are present in SHR aortic smooth muscle cell membranes, but differ from those of normotensive animals regarding the K(+) channels involved in their responses. Moreover, the resting membrane potential (RMP) was significantly more negative in SHR than in normotensive rats. This relative hyperpolarized state is probably due to Ca(2+)-dependent K(+) channels being constitutively open in SHR, since the addition of iberiotoxin caused a significant depolarization of the aortic smooth muscle membranes in this strain.
Fauaz
Grasiele
G
Department of Biophysics, Escola Paulista de Medicina, Federal University of São Paulo, Brazil.
Feres
Teresa
T
Farias
Nelson C
NC
Paiva
Antonio C M
AC
Paiva
Therezinha B
TB
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology; D000068438:Brimonidine Tartrate; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D005260:Female; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D011918:Rats, Inbred SHR; D017208:Rats, Wistar; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects* / Q000502:physiology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D011810:Quinoxalines; D018341:Receptors, Adrenergic, alpha-2; D000068438:Brimonidine Tartrate; D002118:Calcium