Prolactin increases Na+ transport across adult bullfrog skin via stimulation of both ENaC and Na+/K+-pump.
PRL is involved in osmoregulation in lower vertebrates. Its serum concentration starts to increase during the metamorphosis of bullfrog tadpoles. Adult bullfrog skin transports Na(+) from the apical to the basolateral side across the skin. PRL is involved in the regulation of this transport. We investigated the effect of ovine PRL on the epithelial Na(+) channel (ENaC), Na(+)/K(+)-pump, and basolateral K(+) channels, which regulate Na(+) transport across adult bullfrog skin, by measuring the short-circuit current (SCC). At 0.1 microg/ml, PRL had no effect on the SCC. PRL (1 microg/ml) was sufficient to stimulate the SCC since 1 and 10 microg/ml of PRL each increased SCC 1.8-fold. Current-fluctuation analysis revealed that PRL (10 microg/ml) increased the density of active ENaC almost 1.8-fold. The effect of PRL on the Na(+)/K(+)-pump was investigated using apically nystatin-permeabilized skin with Ca-free Na-Ringers' solution on each side. PRL (10 microg/ml) increased SCC in this condition around 1.1-fold, suggesting that PRL stimulates the Na(+)/K(+)-pump [although PRL (1 microg/ml) had no effect on this SCC]. The effect of PRL on basolateral K(+) channels was investigated using apically nystatin-permeabilized skin with high-K Ringer's solution on the apical side. PRL (10 microg/ml) had no effect on the SCC, suggesting that PRL does not affect basolateral K(+) channels. Thus, although PRL stimulates the Na(+)/K(+)-pump, this effect probably contributes less than that on ENaC to the regulation of Na(+) transport across adult bullfrog skin.
Takada
Makoto
M
Department of Physiology, School of Medicine, Saitama Medical University, Moroyama, Iruma-gun, Saitama 3500495, Japan. makokam@saitama-med.ac.jp <makokam@saitama-med.ac.jp>
Hokari
Shigeru
S
D000818:Animals; D004594:Electrophysiology; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D011388:Prolactin / Q000494:pharmacology*; D011892:Rana catesbeiana / Q000378:metabolism*; D012867:Skin / Q000187:drug effects* / Q000378:metabolism; D012879:Skin Physiological Phenomena / Q000187:drug effects; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013997:Time Factors
D053503:Epithelial Sodium Channels; D015221:Potassium Channels; D011388:Prolactin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase