Inhibitory action of cytochalasin E and ethanol on intestinal glucose absorption in the mouse

Abstract

The inhibitory effect of cytochalasin E, ethanol and the simultaneous incubation of cytochalasin E and ethanol on the intestinal glucose absorption in the mouse was studied in everted sacs of jejunum in vitro. Cytochalasin E at a low concentration of 0.25 µg/ml significantly inhibited the intestinal glucose absorption by 14.04%. The inhibitory effect reached a maximum at a concentration of 1.0 µg/ml with 31.1% and this effect was a dose-dependent. Ethanol at a concentration of 5% significantly inhibited the intestinal glucose absorption by 22.21% and reached a peak of inhibition (37.11%) at 7% ethanol. However, the investigation on inhibitory effect of the simultaneous incubation of cytochalasin E and ethanol indicated that at a low concentration of ethanol (4%) together with the various concentrations of cytochalasin E (0.25 to 1.0 µg/ml), the inhibition was an additive effect. Whereas, the high concentrations of both cytochalasin E (1.0 µg/ml and ethanol (5 to 7%), the inhibitory effect seems to be antagonistic. Morphological examination indicated that the villi of mouse jejunum treated with 1.0 µg/ml cytochalasin E, were shortened and the intestinal absorptive cells contained various sizes of vacuoles in upper portion of cytoplasm. But in ethanol (5%) treated jejunum, there were several vacuoles in the cytoplasm and nuclei of the intestinal absorptive cells. In addition, there were many empty spaces between basement membrane and lamina propria. Morphologic alterations were more pronounced in the mouse treated with the simultaneous exposure of 1.0 µg/ml cytochalasin E and 5% ethanol. They revealed the epithelial cells with cuboidal shapes. deteriorated nuclei and elongated villi. A possible mechanism of cytochalasin E was further investigated in the isolated brush-border membrane of mouse jejunum. The cytochalasin E at the concentrations of 2.5, 5 and 10 (...)/ml significantly inhibited glucose transport across brush-border membrane by 16.07% (P < 0.05), 27.87% (P < 0.05) and 28.46% (P < 0.01), respectively after 30 sec incubation. This effect was a dose-dependent manner. In addition, Lineweaver-Burk plot indicated that cytochalasin E inhibited glucose transport with the same Vmax value and increased Km value from 0.95 x 10 (-3) M to 1.92 x 10 (-3) M. The significant inhibitory effect of ethanol on glucose uptake across brush-border membrane was also observed at the concentration of 5% by 27.49% (P < 0.05) within 60 sec incubation. However, the simultaneous incubation of 2.5 µg/ml cytochalasin E and 5% ethanol could significantly inhibit glucose transport within 10 sec by 10.18% (P < 0.01). Kinetic measurement demonstrated that the simultaneous incubation of cytochalasin E and ethanol caused an increase in Km value that was higher than the effect of cytochalasin E alone, from 0.95 x 10 (-3) M to 2.63 x 10 (-3) M and the same Vmax value. These results suggest that cytochalasin E is possible a competitive inhibitor of glucose at the carrier site on brush-border membrane and ethanol may modify the inhibitory effect of cytochalasin E on glucose transport.