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The effect of monocrotofos (in a concentration of 4.5 X 10(-3)M) on the bioelectric parameters of rabbit intestinal epithelium was compared with a similar effect on these parameters of frog skin. It was demonstrated that the tested pesticide added to the medium on the mucosal side of the intestinal wall or on the external side of frog skin caused no evident changes in the potential difference (PD), short-circuit current (CC) and resistance of the studied tissues. This suggested absence of monocrotophos-binding receptors on the external surface of these epithelial structures. The pesticide applied to the serosal side of the intestine decreased PD and SCC without changing the resistance. Applied to the internal surface of frog skin it raised the PD and SCC with some decrease of the resistance. The different pattern of the response could be due to structural differences and to species-specific differences of these epithelia.

The effect of monocrotophos on the bioelectric parameters of frog skin: potential difference (PD), short-circuit current (SCC), the rate of active sodium ion transport, resistance (R), summed ionic permeability, was studied and it was demonstrated that the tested pesticide added to the medium on the external surface of the skin at the concentrations 4.5 X 10(-3)M and 1.1 X 10(-2)M had no significant effects on these parameters. This might have been connected with the presence on the skin surface mechanisms protecting it against the action of this pesticide. After addition to the medium on the internal side of the skin in a higher concentration it produced an irreversible increase in SCC value and decreased tissue resistance. It seems that the most likely cause of the observed changes were disturbances in the molecular structure of the plasma membrane with its stabilization of the sodium channels in the open position.

The effect of paraquat (in concentrations of 10(-4) and 10(-3) mol/l) was studied on the bioelectric parameters of rabbit small intestine. A short-lasting rise in the potential difference (PD) and some decrease of tissue resistance (R) were observed, particularly after the higher concentration. These changes indicate stimulation of the transport function of the rabbit small intestine as a result of administration of this herbicide. Other tested parameters included determination of the rate of paraquat penetration (at concentration gradient 10(-3) mol/l) across the intestinal wall from the serosal side to the mucosal side and conversely. In the latter case three experimental models were used: first--complete intestinal wall, second--intestinal wall with the serosa stripped off, and third--intestinal wall with the mucosa and serosa removed. Differences were found in these rates depending on the model used. The importance of epithelial cells of the mucosa and subepithelial layers, and mesothelium of the serosa in limiting the penetration of bipirydylium herbicides is stressed.

Investigations were carried out on the effects of several pesticides (Lindan, 2,4-D, p,p-Metoxychlor, Carbaryl, Monolinuron) on the transport ability of the plasma membrane. The experiments were done on isolated skin of the frogs Rana temporaria. The so called short-circuit current technique was used for quantitative evaluation of the transport activity in relation to sodium ions. The effect of the studied substances was studied during 3 hours after their addition to the medium on the external surface of frog skin after a preceding control period of 1-2 hours. A series of long-term experiments was performed also in which the animals were exposed to those pesticides for 14-20 days. The results of the acute experiments failed to demonstrate any significant effect of the studied substances on the plasma membrane, but some weak effects could have been observed in some experiments, at least. The results obtained in the long-term experiment showed that an effect on the plasma membrane could be postulated as regards 2,4-D and Carbaryl. It does not mean, however, that this effect is the only mechanism of the toxic action of these substances on the organism.