Blocking effect of La3+ ions on transmembrane ionic current evoked by intracellular cyclic AMP injection in identified Helix pomatia neurons.

Using the fluorescent probe fura-2 for measurements of the cytoplasmic concentration of free Ca2+ ions [( Ca]in) in combination with conventional current- or voltage-clamp methods, we studied the effects of La3+ ions on the cellular responses evoked by intracellular cAMP (adenosine 3',5'-cyclic monophosphate) injections into isolated Helix pomatia neurons. La3+ ions in submillimolar concentrations decreased cAMP-evoked [Ca]in transients. Transmembrane ionic currents evoked by cAMP injections were completely blocked by La3+ ions (1.0 mM) in all neurons under investigation. La(3+)-induced effects essentially differ from each other in RPa1 (right parietal 1) and LPa3 (left parietal 3) neurons. La3+ ions in milli- and submillimolar concentrations strongly affect different subcellular systems, especially, those which regulate an intracellular calcium concentration.