EFFECT OF ALPHA-TOMATINE AND TOMATIDINE ON MEMBRANE-POTENTIAL OF FROGEMBRYOS AND ACTIVE-TRANSPORT OF IONS IN FROG-SKIN

alpha-Tomatine, a glycoside in which four carbohydrate residues are at tached to the 3-OH group of the aglycone tomatidine, occurs naturally in tomatoes (Lycopersicon esculentum). The glycoalkaloid is reported t o be involved in host-plant resistance against phytopathogens and to h ave a variety of pharmacological and toxicological properties in anima ls and humans. As part of an effort designed to establish the mechanis m of action of glycoalkaloids in cells, frog embryos and frog skin wer e exposed to varying concentrations of alpha-tomatine and tomatidine. alpha-Tomatine increased the fluorescence-measured membrane permeabili ty of frog embryos by about 600% compared with control values; the cor responding value for tomatidine was about 150%. alpha-Tomatine also di minished sodium-active transport in frog skin by about 16% compared wi th control values, as estimated from the change in the interstitial sh ort-circuit current. Tomatidine had no effect on frog skin. As these f indings complement similar results with glycoalkaloids from potatoes a nd eggplants, the fundamental mechanism governing their action both ag ainst fungi, insects and other phytopathogens and in animal and human cells may be disruption of cell membranes and changes in ion fluxes an d interstitial currents of the membranes. The described methodologies should make it possible to define the relative potencies of both adver se and beneficial effects of glycoalkaloids and metabolites in cell me mbranes without the use of animals. (C) 1997 Elsevier Science Ltd.