Effect of diabetes on Na(+)-H+ exchange by single isolated hepatocytes

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Abstract
We used the fluorescent dye 2',7'-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF) to examine intracellular pH (pHi) regulation in single hepatocytes isolated from control rats and rats with either spontaneous or drug-induced diabetes mellitus (DM). In the absence of CO2-HCO3-, both control and DM cells recovered from cellular acid loads applied by the NH4+ prepulse technique. Because the pHi recovery was blocked by either Na+ withdrawal or ethylisopropylamiloride in both control and DM cells, it was presumably mediated by Na(+)-H+ exchange. In the control cells, the pHi threshold above which the rate of change of pHi (dpHi/dt) was zero was 7.06, and the slope of the dpHi/dt-pHi relationship was -0.030 s-1. In the DM cells, the pHi threshold was 7.22 and the slope was -0.017 s-1. Thus, at pHi values below approximately 6.9, the pHi recovery was slower in the DM cells. Inasmuch as we observed no difference in the cellular buffering power between control and DM cells, diabetes inhibits Na(+)-H+ exchange within this low pHi range. At pHi values above approximately 6.9, however, Na(+)-H+ exchange was apparently stimulated by diabetes. Thus diabetes induces two distinct alterations of Na(+)-H+ exchange, an alkaline shift in pHi threshold and decrease in slope. Treatment of diabetic rats with insulin for 48 h restored both Na(+)-H+ exchange parameters to normal. On the other hand, insulin added in vitro to DM cells for 2-5 h shifted the threshold toward the control value without affecting the slope, thus leading to a further inhibition of Na(+)-H+ exchange over the entire pHi range.(ABSTRACT TRUNCATED AT 250 WORDS)