Alpha-adrenoceptor subtypes of dog saphenous vein: another unusual property.
The functional relationship between vascular smooth muscle alpha1- and alpha2-adrenoceptor (AR) subtypes was investigated by simultaneous measurement of contractile and fluorescence ratio in fura-2 loaded rings of dog saphenous vein (DSV). Prazosin, as well as rauwolscine, at 0.1 microM, substantially antagonized contractions and associated cytosolic [Ca2+] rises induced by UK 14304, while rauwolscine, as well as prazosin, antagonized similar effects of phenylephrine (PE). These antagonisms were characterized by a parallel rightward shift of the concentration-response curves. In the absence of extracellular Ca2+, PE as well as UK 14304 caused simultaneous transient elevation of contractile force and cytosolic [Ca2+], although the UK 14304 responses were smaller than PE responses. We propose that DSV smooth muscle cells possess interacting alpha1- and alpha2-ARs which have overlapping functional domain sensitive to the agonists and antagonists of either alpha-AR subtype. Both alpha-AR subtypes appear to utilize similar signaling mechanisms via Ca2+ release from the same intracellular stores and Ca2+ entry across the plasma membrane.
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Department of Physiology, Faculty of Medicine, The University of Hong Kong, China.
Kwan
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D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D000068438:Brimonidine Tartrate; D002118:Calcium / Q000502:physiology; D004285:Dogs; D005260:Female; D005453:Fluorescence; D016257:Fura-2; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D010656:Phenylephrine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000145:classification* / Q000187:drug effects / Q000502:physiology*; D012501:Saphenous Vein / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure*; D015398:Signal Transduction / Q000502:physiology; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D015016:Yohimbine; D000068438:Brimonidine Tartrate; D011189:Potassium Chloride; D002118:Calcium; D016257:Fura-2; D011224:Prazosin