| Animal venoms contain a diversity of protein toxins designed for fast immobilization of the prey. Many of these toxins target voltage-gated calcium channels either by blocking ion-conducting pathway or by interacting with the gating mechanism. In this work we investigated the selectivity of two toxins from Arachnids venoms, which modify gating of voltage-gated calcium channels in freshly dissociated rat central and peripheral neurons.; Kurtoxin, a member of α-scorpion toxins family, was first introduced as an antagonist of low-threshold calcium channels. In heterologous systems, kurtoxin potently and selectively inhibited α1H and α1G calcium channel types. In neurons, however, kurtoxin effectively blocked T-, P-, N-, and Bay K 8644-enhanced L-type Ca2+ channel currents. While the toxin consistently behaved as a gating modifier, its effects on channel activation, inactivation, and deactivation varied with each calcium channel type.; ω-Agatoxin-IVA, a peptide isolated from the venom of the spider Agelenopsis aperta, was first characterized as a highly selective inhibitor of P-type calcium channels. Our experimental data confirmed that nanomolar concentrations of the toxin selectively and potently inhibit these channel in freshly isolated rat central neurons. However, at higher concentrations (≥1 μM) ω-Agatoxin-IVA affected N-type Ca channels, as well as high-threshold channels that displayed the pharmacological signature of Q-type calcium channels but resembled P-type in their gating properties. Despite particular loss of selectivity, high concentrations of ω-Agatoxin-IVA did not affect voltage-activated sodium, potassium, and T- and L-type calcium channels.; Study of the toxins' selectivity has led to an observation that in cerebellar Purkinje neurons, as well as in neurons dissociated from the subthalamic nucleus, calcium channel currents are carried exclusively through pharmacologically identified P/Q-, N-, and L-type calcium channels. These observations presented a valuable opportunity to isolate L-type Ca channel currents and investigate its biophysical properties in native neurons. Our preliminary data demonstrated that inactivation properties of L-type Ca channels in Purkinje and subthalamic neurons display significant differences. In addition, pronounced steady-state inactivation of these channels in subthalamic neurons may contribute to unique characteristics of plateau potentials in these cells. |
