The Journal of Neurophysiology Vol. 77 No. 2 February 1997, pp. 690-701
Copyright ©1997 The American Physiological Society

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

Baojian Yu and Patricia Shinnick-Gallagher

Department of Pharmacology and Toxicology, The University of Texas Medical Branch at Galveston, Galveston, Texas 77555-1031

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%). -Conotoxin GVIA (CgTx GVIA, 1 µM) in saturating concentrations inhibited 30% of I_Ca, whereas -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. -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, _1E, and R-type calcium currents, but remains unclassified.

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