MECHANISM OF THE ENHANCING EFFECT OF SORBITOL ON ILEAL CA UPTAKE IN RAT ENTEROCYTES

The effect of sorbitol on Ca uptake by isolated ileal epithelial cells was investigated. Intestinal cells were isolated from rat ileum by me chanical vibration. Ca-45 uptake was approximately 2 times higher in c ells exposed to 200 mM sorbitol of D-alanine than in control cells. Th is enhancing effect of sorbitol on percentage Ca uptake decreased with increasing Ca concentrations in the incubation medium. suggesting an effect on Ca entry velocity. The addition of 10 mu M nifedipine or 200 mu M verapamil to the incubation medium was devoid of any effect on C a uptake in ileal cells, whereas 100 mu M trifluoperazine or chlorprom azine abolished the stimulatory effect of sorbitol. Finally, the effec t of sorbitol on isolated cells was independent of a measurable change of cellular ATP content. In conclusion, the stimulatory effect of sor bitol on ileal Ca uptake is probably exerted through mechanisms other than an increase in intracellular ATP concentration. Sorbitol may enha nce enterocyte Ca transport via a direct interaction with calmodulin a nd/or the Ca pump. It may also exert its effect through an inhibition of the basolateral Na Ca exchanger.