Synaptogenesis and calcium current distribution in cultured leech neurons

The distribution of calcium (Ca²⁺) currents was studied by loose-patch technique in Retzius cells isolated from the leech central nervous system. Ca²⁺-tail currents were recorded in patches held at the equilibrium potential for potassium (E(K)). Measurements were made from single cells and paired cells that had formed chemical or electrical synapses in culture. In single Retzius cells, Ca²⁺ currents in the stump of the initial process were three times larger than in the middle part of the soma; intermediate amplitudes were found in the polar region of the soma. After the formation of chemical synapses, Ca²⁺ currents at the stumps of postsynaptic cells and in the polar region of the somas of presynaptic cells were reduced. The formation of electrical synapses did not affect Ca²⁺ current distribution.