Dominance of P/Q-type calcium channels in depolarization-induced presynaptic FM dye release in cultured hippocampal neurons.
Bottom Line: Analysis of the release kinetics and the fractional release amplitude demonstrate that, whereas in only 15% of the synapses release depended exclusively on P/Q-type channels, the majority of synapses (85%) contained both N- and P/Q-type channels.Nevertheless, the kinetics of FM dye release in synapses containing both channel types was determined by the P/Q-type channels.Together, our data suggest a more direct coupling of P/Q-type channels to synaptic release compared to N-type channels, which may explain the high prevalence of neurological P/Q-type channelopathies.
Affiliation: Division of Physiology, Medical University Innsbruck, Fritz-Pregl-Str. 3, 6020 Innsbruck, Austria.Show MeSH
Related in: MedlinePlus
Mentions: Having established the basic properties of presynaptic FM dye release we next pharmacologically dissected the dependence of release at 40 mM [K+] on Ca2+ channels in order to reveal the contribution of the two major presynaptic channels P/Q- (CaV2.1) and N-type (CaV2.2). Dependence of FM dye release on CaVs was first confirmed by applying the universal Ca2+ channel pore blocker cadmium (Cd2+; 1 mM), which completely abolished the loss of FM dye fluorescence (Fig. 3B). In order to test which types of presynaptic Ca2+ channels mediate [K+]-induced FM dye release we used individual or combined application of CTx and Aga at concentrations known to be highly specific for blocking N- and P/Q-type channels, respectively (Catterall et al., 2005). Incubation with CTx did not affect release kinetics and Rf (Fig. 3), suggesting that FM dye release induced by 40 mM [K+] does not critically depend on N-type channels. In contrast, treatment of cultures with Aga resulted in reduced amplitude and prolonged release kinetics. The combined application of CTx and Aga further reduced amplitude to approximately 50% of control and increased time constants more than 3-fold (Fig. 3C, D). These effects were most strikingly revealed by a reduction of the fractional release amplitude (Rf) to 71% in Aga-only-treated neurons and to 29% in the combined CTx/Aga treatment. This synergistic effect of CTx and Aga indicates that the majority of synapses contain both N- and P/Q-type channels. Nevertheless, only P/Q-type channels can fully compensate the loss of N-type function, whereas N-type channels can compensate the loss of P/Q only with reduced efficacy.
Affiliation: Division of Physiology, Medical University Innsbruck, Fritz-Pregl-Str. 3, 6020 Innsbruck, Austria.