개구리 皮膚의 Na 輸送에 關與하는 Dopamine係 = Dopaminergic System Involved in Sodium Transport of Frog Skin

다국어 초록 (Multilingual Abstract)

To ascertain the existence of dopaminergic receptors involved in active transport of sodium in the frog skin and to delineate the physiological role, the effects of dopamine (DA), apomorphine (Apo) and bromocryptine (BRC) on the potential difference (PD), short-circuit current (SCC) and total skin conductance (TSC) of the isolated frog skin, as well as the influences of dopaminergic and alpha-adrenergic blockers upon the effects of dopaminergic agonists were studied in Rana nigromaculata.
PD and SCC were determined by utilizing the Ussing technique. Both sides of the isolated frog skin were perfused with Ringer solution for cold-blooded animal. All the drugs were applied to the serosal side of the skin.
Results were summarized as follows :
1. The responses to DA(6.5×10^-6 - 2.0×10^-4M), Apo(3.74×10^-6 - 3.74×10^-4M), and BRC(1.53×10^-6 - 4.60×10^-5M) were characterized by elevation of PD and SCC roughly in a dose-related fashion, but the maximal effects attained by DA were greater than those of Apo and BRC. Both Apo and BRC induced graeater increases in PD than SCC, resulting in slight decrease of TSC, whereas no change in TSC was noted with DA.
2. These increments of PD and SCC were inhibited by dopaminergic blockers, such as haloperidol (8.0×10^-5M), metoclopramide (1.0×10^-4M) and sulpiride (8.8×10^-5M).
3. The stimulatory effects of dopamine on PD and SCC were significantly inhibited also by prazosin (2.6×10^-6M), a specific alpha-1 adrenoceptor blocker and were completely abolished by phenoxybenzamine (3.3×10^-6M), an irreversible alpha-adrenoceptor blocking agent.
4. Norepinephrine (6×10^-8 -6×10^-5M), produced increases in PD and SCC. However, these effects were inhibited by prazosin but not influenced by sulpiride pretreatment.
These results suggest that the dopaminergic system may play a role in the control of sodium transport in the frog skin, and that alpha-adrenoceptors may also be involved in the dopamine-induced increase of sodium transport. However, based on evidence at hand, no conclusion could be drawn on the subtypes of dopamine receptors mediating in the stimulation of sodium transport in the frog skin.