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 expe riments, however, the neurological observations with it are rather conflict ing. The cause of this controversiality is not known but relates to some hu man disorders such as Alzheimer's disease and others as well. We studied the time-dependent actions of AlCl3, base solutions on resting m embrane potential (E-m), input resistance (R-in) and spike shape in giant n eurons 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 diffe rences in the effectiveness of the various Al solutions depending on the ti me of storage before use in the experiments (0, 2 and 6 days at room temper ature). Freshly prepared and applied Al solutions caused a significant and dose-dependent depolarization with a concomitant decrease of R-in and the a mplitude of the action potentials, but the 6 days solutions induced a hyper polarization. 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 dir ect membrane effects. Our experiments show that Al can induce differential membrane effects depen ding 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 co uld hyperpolarize the neuronal membrane. We suppose, that the time-dependen t equilibrium of various aluminum complexes plays a role in generating cont roversies in this field and emphasize again the importance of standardizati on of the experimental protocol.