To ascertain the existence of tryptaminergic receptor involved in active transport of sodium in the frog skin and to delineate its physiological role, the effects of 5-hydroxytryptamine (5-+JT)on the potential difference (PD), short-circuit current (SCC) and total skin?conductance(TSC) of the isolated frog skin, as well as influence of tryptaminergic antagonists and various agents upon the 5-HT effects were studied in Rana nigromaculata.
PD and SCC were determined by utilizing Ussing´s technique. Both sides of the isolated frog skin were perfused with Ringer´s solution for cold-blooded animals. All the drugs, except Amiloride, were administered to the serosal side of the skin. Results were summarized as follows :
1. The responses to 5-FIT were characterized by elevation of PD & SCC, roughly in a dose-related fashion in doses ranging from 1.7x 10-AM to 5.7x 10-´M. The more higher doses produced less effects. 5-HT induce greater increase in PD than SCC. Indicating that TSC is decreased by 5-HT.
2. Similar responses were being observed in Na2SO4 -Ringer solution.But the magnitudes of the increase in both PD and SCC were approximately equal, liitle changes in TSC were noted, seggesting that the changes of PD may be, at least in part. Dependent upon the increased outflux of chloride ions. The stimulatory effects of 5-HT on PD & SCCwere abolished by cEAMP(5mM) and amiloride (IX 10-4M).
3. The 5-HT induced increments of PD & SCC were significantly in"ibited by methysergide (8.5X 10´M), a specific 5-HT1 receptor blocking agent, whereas ketanserine, a specific 5-HT2 antagonist did not influence the effects of 5-FIT.
It is concluded from these results that the tryplaminergic system might play role in the control of sodium transport in the frog skin. It is further suggested that the subtypes which indicate these effects might be of 5-Hti -type and cAMP might be involved in the effects as a second messenger.
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