Calcium antagonist binding sites in the rat central nervous system

Abstract Some of the calcium antagonists with diverse structures are considered to specifically block voltage dependant calcium ion channels of excitatory membranes. Each drug acts on a specific site of the calcium ion channel. Receptor binding experiments with use of tritiated Ca antagonist make it possible to examine the functional sites of these drugs. In this paper, we performed binding experiments and autoradiographic studies Ca ion channel antagonist binding sites using tritiated nitrendipine(NTD) in the rat brain. Brain P2 fraction was prepared, and saturation analysis and kinetic studies at the temperature of 0°C, 25°C and 37°C were performed. In addition, competitive studies by various Ca antagonists were done. The in vitro autoradiographic study was done as follows: After cryostat sections of the rat brain were incubated with 2nM 3H-NTD, a tritium sensitive film was apposed on the slides in the dark and stored for 4 weeks at 4°C. As control, experiments were done with sections to which 10#x2212;5 M nifedipine was added at the same time. As preliminary experiments of autoradiography, saturation analysis on cryostat sections at 0°C was done, with results showing a Kd value of 60pM. Autoradiographic studies of 3H-NTD revealed that specific binding sites were diffusely distributed in the neuronal elements with dominancy in the superior colliculus, hippocampus and interpeduncular nucleus.