Time-dependent actions of aluminates on membrane and action potentials of snail neurons

Aluminum (Al) is one of the elements, which is frequently subjected to experiments, however, the neurological observations with it are rather conflicting. The cause of this controversiality is not known but relates to some human disorders such as Alzheimer's disease and others as well. We studied the time-dependent actions of AlCl3 base solutions on resting membrane potential (Em), input resistance (Rin) and spike shape in giant neurons of the snail Helix pomatia L. at pH 7.7 and room temperature (22-24 degrees C) by use of intracellular technique. We reported significant differences in the effectiveness of the various Al solutions depending on the time of storage before use in the experiments (0, 2 and 6 days at room temperature). Freshly prepared and applied Al solutions caused a significant and dose-dependent depolarization with a concomitant decrease of Rin and the amplitude of the action potentials, but the 6 days solutions induced a hyperpolarization. Ouabain (0.1 mM) antagonized the hyperpolarization. The pH (7.1 or 7.7) and the time of the storage in combination also modified the direct membrane effects. Our experiments show that Al can induce differential membrane effects depending on the presence of various aluminum compounds. Namely, the predominate aluminum-monomer at pH 7.7 the Al(OH)4- might cause depolarization but the polynuclear aluminum complexes after polymerization of the monomers could hyperpolarize the neuronal membrane. We suppose, that the time-dependent equilibrium of various aluminum complexes plays a role in generating controversies in this field and emphasize again the importance of standardization of the experimental protocol.