Electrical Potential Profile of the Toad Skin Epithelium

Abstract

The electrical potential profile of the isolated toad skin was recorded, in vitro, by impalement with micropipette-electrodes, when both sides of the skin were bathed with sulfate-Ringer. The outer side of the skin was some 110 mv negative with respect to the inner side. Upon impalement from the outer side, two main positive steps of 40 to 70 my each were found to form the skin potential. The site of measurement of each potential difference was permanently marked in the tissue during recording, by deposition of carmine from the micropipette tip using iontophoresis. Serial histological sections of the skin were prepared and search was then made of the carmine deposits 2 to 6/~ in size, under phase contrast microscopy. By this method the main steps were located at the outer and the inner sides of the stratum germinativum cells. The 9c resistances between the micropipette tip and the bathing solutions were measured during the recording of each potential difference. The resistance at the outer side of the stratum germinativum cells, of 1.09 kilohm, cm ~, was larger than that at their inner side, of 0.30 kilohm, cm e. The stratum germinativum cells maintained a potential difference of --34 mv during short-circuiting of the skin.A m p h i b i a n skins are convenient for the study of several processes involved in ion transport. For better interpretation of these processes further knowledge of the differences in electrical potential, one of the forces driving ions across the skin structures, is necessary. It is well known that the outer side of the skin is negative with respect to the inner side (24). Recent recordings with micropipettes indicate that the skin electrical potential profile is formed by steps (19,5,20), but disagree in their location a n d number. Thus Ottoson et al. (19) recorded one electrical potential step and interpreted it as localized at the basement m e m b r a n e ; Engbaek a n d Hoshiko (5, 8) found two steps a n d suggested that one was located at the outer a n d one at the inner face of the stratum g e r m i n a t i v u m cells; a n d Scheer a n d M u m b a c h (20) described one step at the epithelium a n d one at the tela subcutanea. Frazier (6) working with the toad bladder, a preparation that behaves in m a n y ways as the skin, 795

Active sodium transport and the electrophysiology of rabbit colon

“…When frog skin is bathed by a SO4-Ringer's, Om~ and ~ are each approximately 50-70mV (Engbaek & Hoshiko, 1957;Hoshiko, 1961;Ussing & Windhager, 1964;Cereijido & Curran, 1965) and similar values have been reported for toad skin (Whittembury, 1964;Larsen, 1973). To the extent that the shunt pathway across frog skin is only sparingly permeable to Na, these values may be considered reasonable (minimal) estimated of E~, and E~a and are in reasonable agreement with the values of 64 and 53 mV calculated for rabbit colon.…”

Electrical profiles in the corneal epithelium

“…In the frog cornea, however, the membrane with the greatest resistance is the basal cell inner membrane. Hence, short-circuit current would depolarize the inner membrane, much as it does in frog skin epithelium (Whittembury, 1964). In terms of the active transport systems in cornea-sodium ions by the rabbit (Donn, Maurice & Mills, 1959) A, schematic illustration of the cornea showing the epithelium, a portion of the stroma (st) and the endothelium (e).…”

The origin of the glucose dependent increase in the potential difference across the tortoise small intestine

“…The p.d. across the toad skin (Whittembury, 1964), frog skin (Cereijido & Curran, 1965) and toad urinary bladder (Frazier, 1962) are described by the sum of two positive potential steps. The magnitude and polarity of the potentials across the mucosal and serosal faces of the intestinal epithellum are understandable considering the relative ionic permeability coefficients and the distribution of ions between the cells and their surroundings.…”