Dihydropyridine- and Neurotoxin-Sensitive and -Insensitive Calcium Currents in Acutely Dissociated Neurons of the Rat Central Amygdala

Abstract

Yu, Baojian and Patricia Shinnick-Gallagher. Dihydropyridine- and neurotoxin-sensitive and -insensitive calcium currents in acutely dissociated neurons of the rat central amygdala. J. Neurophysiol. 77: 690–701, 1997. The central amygdala (CeA) is an area involved in emotional learning and stress, and identification of Ca2+ currents is essential to understanding interneuronal communication through this nucleus. The purpose of this study was to separate and characterize dihydropyridine (DHP)- and neurotoxin-sensitive and -resistant components of the whole cell Ca2+ current ( I Ca) in acutely dissociated rat CeA neurons with the use of whole cell patch-clamp recording. Saturating concentrations of nimodipine (NIM, 5 μM), a DHP antagonist, blocked 22% of I Ca; this NIM-sensitive (L-type) current was recorded in 68% of CeA neurons. The DHP agonist Bay K 8644 (5 μM) produced a 36% increase in I Ca in a similar proportion of CeA neurons (70%). ω-Conotoxin GVIA (CgTx GVIA, 1 μM) in saturating concentrations inhibited 30% of I Ca, whereas ω-agatoxin IVA (Aga IVA, 100 nM), in concentrations known to block P-type currents, did not affect I Ca. Higher concentrations of Aga IVA (1 μM) alone reduced I Ca by 34%, but in the presence of NIM (5 μM) and CgTx GVIA (1 μM) blocked only 18% of I Ca. ω-Conotoxin MVIIC (CgTx MVIIC, 250 nM) reduced I Ca by 13% in the presence of CgTx GVIA (1 μM). Application of NIM (5 mM), CgTx GVIA (1 μM), and Aga IVA (1 μM) blocked ∼67% of I Ca. A similar portion (63%) of Ca2+ current was blocked with CgTx MVIIC (250 nM) in the presence of NIM (5 μM) and CgTx GVIA (1 μM). The current resistant to NIM and the neurotoxins represented 37% of I Ca, whereas in neurons not having L-type currents the resistant current made up ∼53% of I Ca (49 ± 2%, mean ± SE). The resistant current activated at around −40 mV and peaked at ∼0 mV with half-activation and -inactivation potentials of −17 and −58 mV and slopes for activation and inactivation of −5 and 13 mV, respectively. The resistant current was sensitive to Cd2+ (IC50 = 2.5 μM) and Ni2+ (IC50 = 86 μM), was larger in Ca2+ than in Ba2+ (ratio = 1.31:1), and showed a moderate rate of decay. In summary, our results show that the high-voltage-activated calcium current in rat CeA neurons is composed of at least four pharmacologically distinct components: L-type current (NIM sensitive, 22%), N-type current (CgTx GVIA sensitive, 30%), Q-type current [Aga IVA (1 μM) and CgTx MVIIC sensitive, ∼13–18%], and a resistant current (Non-L, -N, and -Q current, 33 ∼ 37%), amounting to 37–53% of the total current. The resistant current has some electrophysiological and pharmacological characteristics in common with doe-1, α1E, and R-type calcium currents, but remains unclassified.