COMBINED STUDY OF PURINERGIC TRANSDUCTION USING CRYSTALLOGRAPIC AND ELECTROPHYSIOLOGICAL TECHNIQUES V. A. Panchenko, F. Rodrigues-Pascual^*, M. T. Miras-Portugal^*, O.A.Krishtal, A. A. Bogomoletz Institute of Physiology, Kiev, Ukraine, ^*Departamento de Bioquimica, Facultad de Veterinaria, Universidad Complutense Madrid, Spain.

The purinergic transduction in mammalian brain is not completely investigated by this moment. The aim of this study was to compare the space distribution of diadenosine polyphosphates binding sites in rat brain by the means of autoradiography with possible contribution of this compounds in synaptic transmission mechanisms studied electrophysiologicaly. The distribution of the diadenosine tetraphosphate (Ap4A) high affinity binding sites has been studied in rat brain by autoradiographic method using [3H]-Ap4A as the ligand. Due to specific activity of the labelled ligand, all of the tissues binding experiments were carried out to 1 nM concentration. The Ap4A binding sites were widespread but heterogeneously distributed throe the rat brain. The range of densities was from 3 to 15 fmol/mg tissue in grey matter areas, while white matter was devoid of specific binding, showing background levels. In electrophysiological study the action of Ap4A on potential-dependent Ca channels was studied. Ap4A was found to cause a potentiation of N-type Ca⁺⁺ channels by 21+/-6% (n=12). This potentiation was observed in hippocampal CA3 neurons but not in cerebellar Purkinje neurons. The pharmacology of such potentiation was typical for N-channels properties i.e. it was blocked by 5 micromolar of w-Conotoxin but not 50 micromolar nimodipine. It was possible to compare the data obtained by these two techniques and make a correlation in space distribution and functional properties of Ap4A receptors. In conclusion, our results support the existence of Ap4A specific binding sites and their contribution into Ca-regulated synaptic mechanisms.