?-Agatoxin-TK is a useful tool to study P-type Ca channel-mediated changes in internal Ca and glutamate release in depolarised brain nerve terminals

Inhibition of Evoked Glutamate Release by Neurosteroid Allopregnanolone Via Inhibition of L-Type Calcium Channels in Rat Medial Prefrontal Cortex

“…Thus, one possible mechanism for the inhibitory effect of allopregnanolone on the PKA activation is that allopregnanolone may have an inhibitory effect on extracellular calcium influxevoked PKA activation. To test this hypothesis, we used high K + , which was only calcium channel-dependent (Sitges and Galindo, 2005;Lingamaneni and Hemmings, 1999), to induce the extracellular calcium influx-evoked PKA activation and then observed the effect of allopregnanolone on high K + -evoked PKA activation. The result showed that allopregnanolone could significantly inhibit the high K + -evoked PKA activation.…”

“…To test if allopregnanolone had an inhibitory effect on extracellular calcium influx-evoked PKA activation through calcium channels, here we used another depolarizing agenthigh K + that was only calcium channel-dependent (Sitges and Galindo, 2005;Lingamaneni and Hemmings, 1999), rather than veratridine that was both sodium channel-and calcium channel-dependent (Sitges and Galindo, 2005;Lingamaneni and Hemmings, 1999), to induce the extracellular calcium influx-evoked PKA activation. In the meantime, we used high concentration of ryanodine (10 mM) to block intracellular calcium release from the endoplasmic reticulum (Meissner, 1986).…”

Antiepileptic Drugs Targeting Cerebral Presynaptic Ion Channels Reduce Cerebral Excitability Decreasing Glutamate Release

“…Nevertheless, with the selective Ca 2+ indicator dye, fura-2, the changes in the internal concentration of Ca 2+ concomitant to the changes in cerebral presynaptic Ca 2+ channels permeability can be monitored directly in the cerebral isolated nerve endings. Using this technique it has been shown that among the several types of Ca 2+ channels present in neurons, those sensitive to ω-agatoxin-IVA and to ω-agatoxin-TK, two peptides isolated from the venom of the spider Agelenopsis aperta, were particularly implicated in neurotransmitter release from cerebral nerve endings (Turner et al, 1992;Sitges & Chiu, 1995a;1995b;Carvalho et al, 1995;Sitges & Galindo, 2005). P/Q type Ca 2+ channels are pharmacologically characterized by their sensitivity to the above mentioned ω-agatoxins.…”

“…In the present chapter I describe the strategies that we have used for investigating the effects of several compounds known for their anticonvulsant properties, including several of the most commonly used antiepileptic drugs of the first and second generations, as well as of the new potential antiepileptic drug, vinpocetine on cerebral presynaptic ionic channels. For discriminating the effects of those compounds on presynaptic Na + and Ca 2+ channels, we first used depolarizing strategies, such as veratridine that triggers the entrance of Na + by activation of cerebral presynaptic Na + channels even when the participation of Ca 2+ channels is eliminated, or such as a high external concentration of K + , that activates cerebral pre-synaptic Ca 2+ channels even when the participation of Na + channels is eliminated (Sitges & Galindo, 2005;Sitges et al, 2007a;2007b). More recently, we also test the effects of antiepileptic drugs in the cerebral nerve endings in vitro using 4-aminopyridine as depolarizing strategy.…”

“…Neurotransmitter release evoked by veratridine in synaptosomes isolated from the whole brain or different brain regions is also highly sensitive to the blockade of Na + channels with tetrodotoxin and absolutely dependent on the presence of external Na + , but is independent of external Ca 2+ (Sitges, 1989;Sitges & Chiu, 1995a;Galindo & Sitges, 2004;Sitges & Galindo, 2005). This Ca 2+ independence of veratridine induced responses is particularly valuable as it allows testing the inhibitory effect of compounds on responses selectively mediated by activation of presynaptic voltage sensitive sodium channels in the cerebral isolated nerve endings.…”