J Basic Clin Physiol Pharmacol 1992 Jan 01;31:81-97. doi: 10.1515/jbcpp.1992.3.1.81.

Effect of benzodiazepine ligands on Ca2+ channel currents in Xenopus oocytes injected with rat heart RNA.

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Voltage-dependent Ca2+ channel (VDCC) currents have been measured in Xenopus oocytes injected with heart RNA purified from 7 day old rats, using voltage clamp technique. The currents were evoked by depolarizing voltage steps, using Ba2+ as charge carrier. Electrophysiological analysis of the current revealed two components: a slow, L-type, dihydropyridine (DHP)-sensitive current and a transient, DHP-insensitive, current. The benzodiazepine (BZ) ligands diazepam and Ro5-4864 decreased the current with micromolar affinity, with potency order of Ro5-4864 greater than diazepam greater than clonazepam. The central antagonist Ro15-1788 did not interfere with the effect of these drugs, thus excluding the possible involvement of the "central type" receptor. The slow current that was increased about 3 fold in the presence of 0.5 microM Bay K 8644, was less potentiated when previously treated with Ro5-4864 or diazepam. Current-voltage relation of the peak inward current and the steady state activation curve showed a small shift towards negative potentials in the presence of 50 microM diazepam. It is concluded that the benzodiazepine ligands block DHP-sensitive voltage dependent Ca2+ channels with a very marginal effect on the transient, DHP-insensitive current. Also it is emphasized that Xenopus oocytes can serve as a useful model system to study the pharmacology of these important drugs on cardiac Ca2+ channels.

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Species referenced: Xenopus laevis
Genes referenced: dpys