ISSN:
1432-136X
Keywords:
Active Cl- transport
;
Noradrenalin α-type receptor
;
Acetylcholine
;
Serotonin
;
Tissue resistance
;
Eel, Anguilla japonica
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract After inhibiting ion and water transport with 10-6 mol·l-1 serotonin and 10-6 mol·l-1 methacholine, a muscarinic agonist of acetylcholine, 10-5 mol·l-1 (±)noradrenaline restored the serosa-negative transepithelial potential difference and short-circuit current in a step-like manner, accompanied by an increase in water absorption across the seawater eel intestine. Such recovery by noradrenalin was not obtained after pretreatment with 10-7 mol·l-1 eel atrial natriuretic peptide. This means that the inhibitory mechanisms of serotonin and acetylcholine are different from those of atrial natriuretic peptide. Similarly, 10-7 mol·l-1 clonidine and guanabenz (α2-agonists) also reversed the inhibitory action of serotonin and methacholine, but 10-7 mol·l-1 phenylephrine (α1-agonists) and 10-7 mol·l-1 isoproterenol (β-agonist) did not antagonize serotonin and methacholine actions. Further, the enhancement by 10-5 mol·l-1 noradrenalin was blocked by 10-4 mol·l-1 yohimbine (α2-agonists) and 10-4 mol·l-1 prazosin (α1-agonists), but not by 10-4 mol·l-1 propranolol (β-antagonist). Although relatively high dosage is required to obtain a significant effect, and discrimination between α1- and α2- is not successful in the present study, these results suggest that noradrenalin acts on an α-type receptor. The α-type receptor may exist on the enterocytes, since the effects of noradrenalin are observed even in the presence of 10-6 mol·l-1 tetrodotoxin. Interestingly, the tissue resistance also increased in parallel with increase in the short-circuit current after treatment with noradrenalin in the posterior part of the seawater eel intestine.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00309666
