The dissertation is devoted to comparative analysis of pharmacological effects of dihydropyridines: nifedipine, nimodipine and nitrendipine on two subtypes LVA Ca2+ channels ("fast" and"slow") in rat thalamic neurons and three types of recombinant T-type Ca2+ channels (?1G, Cav3.1, ?1H, Cav3.2 and ?1I, Cav3.3), functionally expressed in Xenopus oocytes. The isolated thalamic neurons were investigated using the "whole-cell" patch-clamp technique, at a holding potential of -100mV. The investigation of currents induced by poreforming ?1 subunits expression in Xenopus oocytes were done with using the double-electrode technique. In the present study, were investigated dihydropyridine-sensitivity for endogenous LVA Ca2+ channels in rat thalamic neurons, most effective agent was nitrendipine, then nimodipine and nifedipine. Corresponding constants of concentration half-maximal blokade for "fast" channels (IC50) were:: nifedipine-22, nitrendipine-0,14, nimodipine-0,81 µМ, correspondingly. For "slow" channelssame parameters were: nifedipine -28, nitrendipine -0,38, nimodipine -2,2 µМ. We used pharmacological criteria, namely used dihydropyridine-sensitivity, in attempt to distinguish LVA Ca2+ currents in thalamic neurons and shed some light on ?1 subunits composition of underlying channels. To do so, we broke down the overall LVA Ca2+ current in isolated neurons from LD thalamic nucleus of 14-17 day-old rats onto two components based on the difference in the rate of inactivation and examined the effects of dihydropyridines on each of them. These were then compared to the effects of nifedіpine on three subtypes of recombinant of LVA Ca2+ channel ?1 subunits functionally expressed in Xenopus oocytes. At voltages of the maximums of respective currents the drug most potently blocked ?1H (IC50 = 5 µM, max block 41%) followed by ?1G (IC50 = 109 µM, 23%) and ?1I (IC50 = 243 µM, 47%). The mechanism of blockade included interaction with Cav3.1, Cav3.2 and Cav3.3 open and inactivated states. Nifedipine blocked thalamic ILVA,f and ILVA,s with nearly equal potency (IC50 = 22 µM and 28 µM, respectively), but with different maximal inhibition (81% and 51%, respectively).We conclude that Cav3.2 is the most sensitive to nifedipine, and that quantitative characteristics of drug action on T-type Ca2+ channels depend on cellular system they are expressed in. Our present pharmacological data on nifedipine actions, which permitted us to correlate ?1G and ?1I to the ''fast'' and ''slow'' thalamic LVA channels, respectively, provided a molecular substrate to the abstract concepts of ''fast'' and ''slow'' thalamic channels, and allowed one to be more specific in assigning a developmental role to the endogenous ?1I and maybe ?1H and signaling role to ?1G T-channel ?1 subunits. Despite the lack of highly selective T-type channel antagonists, the use of pharmacological agents has revealed that T-type currents contribute to a wide range of physiological processes in normal neural and nonneural tissues. Although there is not a single identifying pharmacological criterion for T-type currents, over 15 classes of drugs are suspected to affect T-type channels. T-type channels may be important therapeutic targets in the treatment of epilepsy, pain resting tremors, asthma, cardiac hypertrophy, cardiac ischemia, hypertension, cancer, and diabetes. It is anticipated that the discovery of more selective T-type channel blockers will further our basic understanding of the molecular composition and physiological functions of T-type channels, and aid in the treatment of a variety of neural and nonneural diseases. Key words: Dihydropyridines, endogenous and recombinant T-type Ca2+ channels, nifedipine, nimodipine, nitrendipine, thalamic neurons, Xenopus oocytes.
