Endocrinology, Vol 101, 1701-1708, Copyright © 1977 by Endocrine Society

ARTICLES

Characterization of the uptake of the methylxanthines theophylline and caffeine in isolated pancreatic islets and their effect on D-glucose transport

ML McDaniel, DC Weaver, CE Roth, CJ Fink, JA Swanson and PE Lacy

The uptake of theophylline and caffeine was determined in isolated pancreatic islets employing a dual isotope procedure with sucrose as an extracellular marker. Islets rapidly accumulated caffeine and theophylline with apparent dissociation constants of approximately 23 and 6 mM, respectively. Theophylline inhibited the uptake of caffeine and caused displacement of caffein from islets. These results indicated a competition by theophylline and caffeine for a common site (binding and/or transport carrier). In addition, theophylline and caffeine inhibited D-glucose transport in a dose-dependent manner and within the limits of the experimental system, this inhibition appeared to be non- competitive. (Bu)2cAMP under similar experimental conditions exerted no effect on D-glucose transport. These results present evidence for a rapid uptake of theophylline and caffeine in pancreatic islets, which is compatible with their immediate cellular effects. In addition, these results demonstrate a direct effect by theophylline and caffeine on D- glucose transport which appears independent of their ability to alter intracellular cAMP levels.

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