HEPARIN MODULATES ADENINE-NUCLEOTIDE HYDROLYSIS BY SYNAPTOSOMES FROM CEREBRAL-CORTEX

The modulatory effect of heparin and dextran sulfate 500,000 (sulfated polysaccharides) was studied on ATPDase and 5'-nucleotidase activitie s. These enzymes participate in the degradation of ATP and adenosine p roduction at the synaptic cleft level. Nucleotide hydrolysis was inhib ited by heparin and dextran sulfate 500,000. For ADP, the inhibition w as more evident at low cation concentrations (0.15 mM Ca2+ or Mg2+), r eaching a maximum of 75%. For ATP, the inhibitory effect was less prom inent and independent of divalent cation concentration, reaching a max imum of 25%. For AMP, the inhibition observed was similar with either relatively high (1 mM) or with low Mg2+ concentrations tested (0.1 mM) and reached a maximum of 35%. K+ did not change the inhibitory potenc y of sulfated polysaccharide suggesting that its effects were not excl usively related to charge interaction. These results suggest that hepa rin and possibly other naturally occurring sulfated polysaccharides ma y have a potential role as modulator of extracellular nucleotide hydro lysis in the synaptic cleft region. (C) 1998 Elsevier Science Ltd. All rights reserved.