Electrophysiological effect of ruthenium red and pH on the skin of the edible frog, Rana esculenta L.

Amphibian skin is a sensitive interface between the organism and the environment. Metal ions from the external environment, some of them being trace elements, act on the amphibian skin. It had been shown that stimulation of tactile receptors affected Na+ transport in the frog skin and changed the potential difference, therefore the aim of this project was to study the effect of ruthenium complex, known as ruthenium red (RR), on the ion transport in this organ in vitro under control conditions, after mechanical stimulation and also in the presence of the Na+ transport inhibitor-amiloride. Three different concentrations of RR (0.12, 1.2, and 12.0 mM) in two different pH values (6.4 and 7.4) were studied in vitro in the Ussing apparatus. The measured electrophysiological parameters were the transepithelial electrical potential difference (PD) and the changes in PD after mechanical stimulation (dPD). The gentle mechanical stimulus was a jet of bath fluid from a peristaltic pump directed on the mucosal surface of isolated frog skin. After mechanical stimulation, transient hyperpolarization invariably occurred (dPD = 1.5 +/- 0.2 mV). In the presence of RR the hyperpolarization was smaller and this diminution was concentration dependent: 0.5 +/- 0.1 mV for 1.2 mM of RR and 0.1 +/- 0.1 mV for 1.2 mM of RR. At pH 6.4 the reactions of the skins on the mechanical and chemical stimuli were smaller, in the presence of amiloride disappearing completely, but after the washing away of amiloride from the experimental organ in pH 6.4 the action of RR was stimulatory. The natural defensive reactions of frog skin related to the ion transport and electrical potential difference are affected or disappear in the presence of ruthenium complex.