Cellular and molecular characterization of Ca2+ currents in acutely isolated, adult rat neostriatal neurons

Abstract

Ca2+ currents in acutely isolated, adult rat neostriatal neurons were studied with whole-cell voltage-clamp techniques. In the vast majority of neurons (approximately 90%, n > 250), currents were exclusively of the high-voltage-activated (HVA) type. HVA currents activated near -40 mV and reached their maximum amplitude near 0 mV. Quasi-steady-state inactivation curves in many neurons were well fitted only with a sum of Boltzmann functions, suggesting that the HVA currents were heterogeneous. Although the block of whole-cell current by Cd2+ was well fitted with a single isotherm having an IC50 of near 1 microM, experiments with organic channel antagonists suggested that at least four types of HVA channels were expressed by most cells. On average, the L-channel antagonist nifedipine (5–10 microM) blocked 31 +/- 10% of the whole-cell current (n = 20), the N-channel antagonist omega- conotoxin GVIA (omega-CgTx) (2–5 microM) blocked 27 +/- 11% (n = 20), and the P-channel antagonist omega-agatoxin IVA (100–500 nM) blocked 21 +/- 10% (n = 18). In many neurons, the block by omega-CgTx was partially or completely reversible. In cells tested with a combination of these antagonists, 34 +/- 17% of the peak Ca2+ current remained unblocked (n = 13). Single-cell expression profiling of medium-sized neurons revealed the presence of rbA and rbB Ca2+ channel alpha 1 subunit mRNAs but low or undetectable levels of rbC mRNA (n = 12). These findings suggest that although adult neostriatal projection neurons do not express significant levels of LVA Ca2+ current, they do express a pharmacologically and structurally heterogeneous population of HVA currents.

Control of Spontaneous Firing Patterns by the Selective Coupling of Calcium Currents to Calcium-Activated Potassium Currents in Striatal Cholinergic Interneurons

“…Ryanodine (15 M) was used to selectively deplete ryanodine-sensitive stores. Cytochrome c (0.01% w/v in final bathing solution) was added as a carrier whenever ryanodine and agatoxins were used (Bargas et al, 1994). In some experiments, a 2 mM concentration of the fast calcium chelator BAPTA was added to the pipette solution.…”

Coordinated Expression of Dopamine Receptors in Neostriatal Medium Spiny Neurons

“…Neostriatal neurons from young adult (Ͼ3 wks) rats were acutely dissociated by procedures similar to those we have described previously (Bargas et al, 1994;Surmeier et al, 1995a). All solutions coming into contact with the tissue during the dissociation procedure were prepared aseptically and nominally RNase-free.…”

“…Whole-cell recordings used standard techniques (Hamill et al, 1981;Bargas et al, 1994). Electrodes were pulled from Corning 7052 glass and fire-polished before use.…”

Muscarinic (m2/m4) receptors reduce N- and P-type Ca2+ currents in rat neostriatal cholinergic interneurons through a fast, membrane- delimited, G-protein pathway

“…Neostriatal neurons from adult (>4 weeks old) rats were dissociated acutely, using procedures similar to those we have described previously (Bargas et al, 1994;Surmeier et al, 1995). In brief, rats were anesthetized with methoxyflurane and then decapitated; brains were quickly removed, iced, and blocked for slicing.…”

“…Standard techniques were used in whole-cell recordings of Bazt currents through Ca*+ channels (Hamill et al, 1981;Bargas et al, 1994). Electrodes were pulled from Corning 7052 glass and fire-polished before use.…”