Electrical and transport characteristics of skin of larval Rana catesbeiana

Abstract

Carefully dissected, mounted, and bathed with Ringer solution, the larval bullfrog skin has a resistance of about 9,000 omega.cm2 and a stable transepithelial electrical potential of about 20 mV (inside +). A short-circuit current of about 2 microA.cm-2 is generated that is comparable in magnitude to the net inward flux of Na+. At open circuit the flux ratio equation for Na+ is not satisfied. Larval skin is less sensitive to ouabain, amiloride, and ADH than adult skin. The current-voltage (C-V) relationship across the preparation is not linear; there are distinct breaks in both the hyperpolarizing and hypopolarizing regions. The former break, at about +130 mV, corresponds with a break observed in adult skin that corresponds with ENa. The shunt resistance (RS) and active pathway resistance (RA) were estimated by C-V curve analysis and by ion substitution. The two methods yielded comparable values with RS about 11 k omega.cm2 and RA about 62 k omega.cm2. It is suggested that transport is limited by the number of entry sites for sodium at the apical border of transport cells.

Stretch-activated cation channel from larval bullfrog skin

“…Structurally, the larval skin is simpler than that of the adult with an outer layer of apical cells supported on a layer of basal cells with intermediate filament-rich skein cells interspersed between the apical and basal cells (Weed, 1933;Robinson and Heintzelman, 1987). Cox and Alvarado showed that the larval skin mounted in an Ussing-type chamber that minimized edge damage to the apical cell layer had very high resistance and generated a small short-circuit current (I sc ) with NaCl Ringer's solution bathing either side of tissue (Cox and Alvarado, 1979). A similar or even greater I sc could be obtained with KCl or other alkali metal cation Ringer's solutions as the outer solution (Cox and Alvarado, 1979), and this current was shown to be carried by a non-selective cation channel that could be activated by amiloride, which is an inhibitor of epithelial sodium channels in the adult skin (Hillyard et al, 1982).…”

“…Cox and Alvarado showed that the larval skin mounted in an Ussing-type chamber that minimized edge damage to the apical cell layer had very high resistance and generated a small short-circuit current (I sc ) with NaCl Ringer's solution bathing either side of tissue (Cox and Alvarado, 1979). A similar or even greater I sc could be obtained with KCl or other alkali metal cation Ringer's solutions as the outer solution (Cox and Alvarado, 1979), and this current was shown to be carried by a non-selective cation channel that could be activated by amiloride, which is an inhibitor of epithelial sodium channels in the adult skin (Hillyard et al, 1982). Subsequent experiments with the larval skin have shown similar stimulation of non-selective cation conductance by acetylcholine and ATP (Cox, 1992;Cox, 1993;Cox, 1997).…”

Different sensitivity to amiloride of body and tail skins of Rana catesbeiana tadpoles during metamorphosis

“…Amiloride affects the Na + channels and reduces the active Na + transport across the adult frog skin: the PD and SCC of the skin are decreased by amiloride. The appearance of amiloride-sensitive PD and SCC is one of the markers of the development of the active Na + transport that is characteristic of the adult frog skin (Cox and Alvarado 1979;Hillyard et al 1982a, b;Takada 1985).…”

“…The system for active Na + transport across the ventral skin of Rana catesbeiana differentiates during metamorphosis, and the differentiation of the transport system is induced by thyroid hormone (Taylor and Barker 1965;Cox and Alvarado 1979;Takada 1989Takada , 1990.…”

Prolactin increases open-channel density of epithelial Na+channel in adult frog skin

“…This transport develops during the climax stages of metamorphosis in the bullfrog, and is due to the development of an epithelial Na + channel (ENaC). Therefore, the appearance of transcellular active Na + transport as SCC and/or ENaC is a marker of the development of adult-type features by the skin (Cox and Alvarado, 1979;Hillyard et al, 1982;Takada, 1985).…”