In this study, it is shown how to transfer tared aliquots of (HCO3 + CO2)-containing luminal fluids directly into the mercury-sealed chamber of a modified Van Slyke apparatus and how to obtain direct as well as indirect manometric determinations of dissolved CO2 ([CO2]f) in each aliquot of such fluids. It is next shown that the pattern of in vitro luminal acidification in an isolated turtle bladder sac depends upon the prior in vivo ambient temperature to which the donor turtle had become adapted. Under in vivo conditions, the food intake, physical activity, and acid excretion of 32 degrees C-adapted turtles are greater than those of 21 degrees C or 26 degrees C-adapted turtles. Under in vitro conditions of incubating isolated bladder sacs (from 21, 26, and 32 degrees C turtles) in (HCO3 + CO2)-containing Ringer media at a single temperature (21 degrees C), the patterns of luminal acidification are as follows: (a) The rate of depletion of luminal [HCO3] is greatest in bladders from the 32 degrees C-adapted turtles. (b) Concomitant decreases in luminal [CO2]f, [HCO3], and pH (the 'CO2-decreasing patterns' of luminal acidification) develop in all bladders from 32 degrees C turtles, in half of those from 26 degrees C turtles, but in less than one-fifth of those from 21 degrees C-adapted turtles: and (c) a CO2-increasing pattern of luminal acidification is found in most of the bladders from 21 degrees C-adapted turtles. A postulated bicarbonate ion-reabsorbing pump is consistent with all of these patterns of luminal acidification.

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