Development of HVA and LVA calcium currents in pyramidal CA1 neurons in the hippocampus of the rat

High voltage activated (HVA) and low voltage activated (LVA) calcium currents were recorded in acutely dissociated CA1 hippocampal pyramidal neurons of the rat during the first three postnatal weeks as well as in adults. Measured in whole cell voltage clamp the amplitude of the HVA calcium current increased steadily and reached adult values after 20 postnatal days (P20). Using the perforated patch configuration with amphotericin B the amplitude of the HVA component was more than five times smaller, but the time course of development was the same. The LVA component also increased with age but reached adult values already around P13. The amplitude and developmental pattern of this component were not different when measured with the perforated patch technique. The results indicate a different role for intracellular modulators on these calcium currents, but exclude them as important factors in the developmental pattern. The fast development of the LVA component could lead to calcium dependent action potentials (and calcium spikes) in immature cells. The complex developmental pattern of the relative amplitude of the two currents will either lead to specific variations in the intracellular calcium homeostasis or will have to be accompanied by an adequate developmental pattern of buffering and extrusion mechanisms.