Influence of cholesterol depletion in plasma membrane of rat brain synaptosomes on calcium-dependent and calcium-independent exocytosis

It is well established that calcium-dependent neurotransmitter release and exocytosis can be regulated by altering the cholesterol content of the plasma membrane. We have compared the influence of cholesterol depletion of synaptosomal plasma membrane by 15 mM methyl-β-cyclodextrin (MCD) treatment on calcium-dependent release of d-[3H]aspartate induced by the calcium ionophore A23187 and on calcium-independent release induced by hypertonic shrinking or polyvalent cations. We found that decrease of cholesterol concentration by 9.3% inhibited calcium-dependent release of d-[3H]aspartate induced by calcium ionophore A23187 by four times while release induced by 300 μM Gd3+, 150 mM and 500 mM sucrose remained unchanged. Further we have investigated the influence of MCD on exocytosis monitored by the fluorescent dye, acridine orange. Cholesterol depletion inhibited calcium-dependent exocytosis induced by calcium ionophore A23187 but had virtually no influence on calcium-independent exocytosis induced by hypertonic shrinking or Gd3+. In summary, we found that the cholesterol content in synaptosomal plasma membrane is important for calcium-dependent exocytosis.