The functional and ultrastructural effects of the organophosphorous insecticides Dursban and Lorsban on the ciliated epithelium of the frog palate in vitro

This study was conducted to assess the ciliotoxic potential of the organophosphorous insecticides Dursban and Lorsban, their active ingredient, chlorpyrifos and their carrier ingredients (blanks). The ciliated epithelium of the frog palate was used as the model for an innervated ciliated system, since chlorpyrifos inhibits nervous system acetylcholinesterase. Frog palates were excised and cultured to form ciliated outgrowths. Outgrowths were monitored with an inverted phase contrast microscope, and ciliary beat frequencies were determined using an optical spectrum analysis system. All compounds caused a decrease in frequency of ciliary beat over time. Concentration-response curves were constructed from data of time to inhibition of ciliary beating. The order of toxicity was Lorsban, Dursban, Lorsban Blank, Dursban Blank, and chlorpyrifos, with Lorsban being the most toxic and chlorpyrifos being the least toxic. ECs estimations were also calculated from these data; and they followed the same order of toxicity as the time to inhibition studies. Samples were examined by electron microscopy to evaluate any ultrastructural effects. All compounds were found to cause mitochondrial damage, including swelling, disruption of cristae, and loss of matrix.

The response of individual cells was monitored immediately after addition of test compounds. Stimulation of ciliary beating was evident immediately after exposure to all compounds. Stimulation was ultimately followed by inhibition, within a time frame (a few minutes to hours) depending on the concentration of the compound in the test medium. Dursban, Lorsban, and both blanks elicited stimulatory effects in the presence of atropine. Atropine blocked the initial stimulatory response only with chlorpyrifos. It appears that in addition to chlorpyrifos some component (s) of the inert ingredients were initially stimulatory but ultimately inhibitory to ciliary beating in the frog palate model.