GLUCOSE-METABOLISM IN DOG INNER MEDULLARY COLLECTING DUCTS

The adenosine triphosphate (ATP) generating pathways of dog inner medu llary collecting ducts (IMCD) were examined in vitro using suspensions of dog IMCD tubules incubated under aerobic and anaerobic conditions. Glucose is always the preferred substrate for this tissue, even iflac tate can be oxidized under aerobic conditions. The metabolism of gluco se proceeds largely towards lactate accumulation in the presence or ab sence of oxygen. Glycogen is also consumed and more markedly so during anoxia. The pentose shunt represents a minor pathway for glucose meta bolism in this tissue. Under aerobic conditions, the net oxidation of glucose to CO2 contributes significantly to the cell energetics, mitoc hondrial and cytoplasmic mechanisms sharing equally the ATP synthesis. In the absence of oxygen, only the cytoplasmic routes of ATP synthesi s are used, but the apparent ATP turnover is markedly reduced. A marke d inhibition of the activity of the Na-K-ATPase during anoxia explains this observation. The utilization of glucose for osmolyte synthesis i s a minor process and appears to be suppressed under anaerobic conditi ons. It is concluded that the ATP turnover is low in dog IMCD cells as compared with that of other nephron segments and is largely dependent upon glucose availability under aerobic or anaerobic conditions.