ALKALINIZATION BY MANDUCA-SEXTA ANTERIOR MIDGUT IN-VITRO - REQUIREMENTS AND CHARACTERISTICS

Manduca sexta anterior midgut alkalinizes its luminal contents in vivo , achieving pH values up to 12 with rates of up to 81.4 mu Eq OH- h(-1 ). The alkalinization rate dropped to 3.0 mu Eq h(-1) within minutes o f mounting the tissue in an Ussing chamber, even though K+ secretion(a s measured by short-circuit transepithelial current and open circuit v oltage) continued at a high rate for several hours. In contrast, cannu lation of the anterior midgut in situ resulted in a preparation that a lkalinized at rates up to 127 mu Eq h(-1) for several hours. Removal o f the head or ventral nerve cord did not interrupt alkalinization. How ever, alkalinization 'could be blocked by increasing the volume of the saline in which the basal side was bathed. The buffer capacity of the saline had no effect on the maximum pH attained or the rate of base s ecretion. Doubling of the drip rate from 0.5 to 1.0 ml min(-1) had no effect on the maximum rate of OH- secretion but resulted in a reductio n of the maximum pH attained from I1 to 8.5. These data suggest releas e of an alkalinization factor from the basal aspect of the gut that ma y act by altering the passive H+ permeability of the tissue. (C) 1998 Published by Elsevier Science Inc. All rights reserved.