Isolated segments of renal tubules prepared from rat kidney cortex were capable of sustained rates of gluconeogenesis when lactate served as substrate. An increase in external Ca(++), or the addition of parathyroid hormone at a fixed Ca(++) concentration led to enhanced rate of gluconeogenesis. However, parathyroid did not increase gluconeogenesis in the absence of external Ca(++) even though it caused a rise in 3'5' AMP whether Ca(++) was present or absent. Metabolite profiles showed that either an increase in external Ca(++), or the addition of hormone in the presence of calcium led to qualitatively very similar changes. However, the addition of hormone had little effect upon metabolite levels in the absence of extracellular calcium even though an increase in extracellular H(+) enhanced gluconeogenesis under similar conditions. These results are discussed in relationship to the close association of 3'5' AMP and Ca(++) in a variety of cellular systems.
Adenine Nucleotides Adenosine Triphosphate