Actions of carbaryl on the ionic transport across the isolated skin of Rana esculenta

1. Carbaryl, a carbamate used as a pesticide, increases the short-circuit current (SCC) across the isolated frog skin in a dose-dependent manner. 2. This effect is due to the stimulation of sodium absorption and chloride secretion. 3. Carbaryl action on short-circuit current is unrelated to its inhibitory power on cholinesterase; this statement is supported by two experimental results: (a) carbaryl is equally active on both sides of the skin, (b) atropine pretreatment does not inhibit the carbaryl action on SCC.     

Active transport of chloride across skin isolated from Rana esculenta]

The effect of SITS, ouabain and acetazolamide on potential difference (E) and short-circuit current (ccc) across isolated frog skin after Amiloride treatment have been investigated. It has been found that Amiloride (3.5 . 10(-5)M) reverses the E and ccc values. After Amiloride treatment, with the use of SITS (6 . 10(-4)M) positive values of E and ccc have been measured while Ouabain (10(-4)M) only slightly reduces the reversed E and ccc values. On the other hand the effect of Acetazolamide (6 . 10(-4)M) is additional to the effect of SITS. It is suggested that the frog skin possesses an active transport for Cl-, as demonstrated by the use of Amiloride, and that it is carried out by two distinct mechanism: the first SITS and Acetazolamide sensible, the second one sensible to Strofantine.     

Prostaglandin E2-stimulated glandular ion and water secretion in isolated frog skin (Rana esculenta)

Summary Prostaglandins are known to stimulate the active sodium absorption in frog skin. In this paper it is shown that prostaglandin E₂ (PGE₂) stimulates an active secretion of Cl^–, Na⁺, and K⁺ from the skin glands inRana esculenta. The active Cl secretion is enhanced more than the Na and K secretion. Therefore, in skins where the Na absorption is inhibited by amiloride, the addition of PGE₂ results in an increase in the short-circuit current (SCC). The PGE₂-stimulated Cl secretion could be inhibited by the presence of ouabain or furosemide in the basolateral solution or diphenylamine-2-carboxylate in the apical solution. The PGE₂-stimulated Cl secretion was enhanced by the phosphodiesterase inhibitor, theophylline, indicating that the effect of PGE₂ was caused by an increase in the intracellular cAMP level in the gland cells. The calcium ionophore A23187, which increases the PGE₂ synthesis in frog skin, stimulated the glandular Cl secretion. This secretion could be blocked by the prostaglandin synthesis inhibitor indomethacin, indicating that A23187 acts by increasing the prostaglandin synthesis and not by a direct action of Ca²⁺ ionsper se. The net water flow (J _w) and the Cl secretion were measured simultaneously under the conditions outlined above. The stimulation, inhibition, and the time-course of the outward-directedJ _w were similar to the change observed for the Cl secretion. These results show that PGE₂ stimulates a glandular secretion of Cl and water in frog skin, probably by increasing the cAMP level in the gland cells.     

Prostaglandin E2 enhances the sodium conductance of exocrine glands in isolated frog skin (Rana esculenta)

Summary Prostaglandins are known to stimulate the active transepithelial Na⁺ uptake and the active secretion of Cl^– from the glands of isolated frog skin. In the present work the effect of prostaglandin E₂ (PGE₂) on the glandular Na⁺ conductance was examined. In order to avoid interference from the Na⁺ uptake and the glandular Cl^– secretion the experiments were carried out on skins where the Cl^– secretion was inhibited (the skins were bathed in Cl^– Ringer's solution in the presence of furosemide, or in NO ₃ ^– Ringer's solution), and the active Na⁺ uptake was blocked by the addition of amiloride. Transepithelial current, water flow and ion fluxes were measured. A negative current was passed across the skins (the skins were clamped at –100 mV, basolateral solution was taken as reference). When PGE₂, was added to the skins under these experimental conditions, the current became more negative; this was mainly due to an increase in the Na⁺ efflux. Together with the increase in Na⁺ efflux a significant increase of the water secretion was observed. The water secretion was coupled to the efflux of Na⁺, and when one Na⁺ was pulled from the basolateral to the apical solution via this pathway 230 molecules of water follwed. From the data presented it is suggested that this pathway for Na⁺ is confined to the exocrine glands.     

Transepithelial transport of sodium and chloride ions in isolated skin of the frog,Rana esculenta L

Isolated frog skin, mounted in a Ussing apparatus, was investigated electrophysiologically. Application of amiloride, an inhibitor of sodium ion transport, and bumetanide, known to block the transport of chloride ions, revealed the effect of these ions on PD, both under control conditions and following mechanical stimulation. Under control conditions, mechanical stimulation of the skin caused hyperpolarization, i.e. a transient increase in the electrical potential difference. Preincubation in the presence of amiloride, or amiloride plus bumetanide, brought about both a decrease in electrical potential and an inhibition of the reaction upon stimulation. On the other hand, incubation with bumetanide resulted in a decrease in electrical potential, but did not affect the skin reaction after mechanical stimulation. The above results indicate that hyperpolarization of the frog skin following mechanical stimulation is caused by enhanced transepithelial transport of sodium ions which, in turn, is induced by stimulation of sensory receptors.