The effect of lead (Pb2+) on electrophysiological properties of calcium currents in F77 neuron in Helix aspersa

Ion channels are responsible for control of cell function in excitable tissues such as heart and brain and also in organs and tissues traditionally thought to be non- excitable including liver and epithelium. In the present research, the effect of lead (Pb2+) on Ca2+ -dependent action potential and currents was studied in F77 neuronal soma membrane of Helix aspersa. For this purpose, action potential generation and Ca2+ currents were investigated in the absence and presence of Pb2+ using two-electrode voltage clamp and current clamp methods. Two distinct types of high voltage activated (HVA) calcium currents were recorded. In this respect, one of them was sensitive to nifedipine (1 µM) and the other one was resistant to nifedipine. Extracellular application of Pb2+ at concentrations of 0.6 and 3 µM suppressed the firing behavior of F77 neurons. It also decreased the amplitude and the duration of calcium action potentials. The voltage clamp findings demonstrated that lead blocked more than 50% of HVA Ca2+ currents. The blocking effect of Pb2+ on Ca2+ was time-dependent. Therefore, it can be concluded that Pb2+ may alter the bioelectrical properties of F77 neuron through blocking high voltage activated Ca2+ currents, particularly L-type that are nifedipine sensitive.