Cellular and molecular characterization of Ca2+ currents in acutely isolated, adult rat neostriatal neurons.
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.
Instituto de Fisologia Celular, Universidad Nacional Autonoma de Mexico, Mexico.
J
J
Bargas
A
A
Howe
J
J
Eberwine
Y
Y
Cao
D J
DJ
Surmeier
D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002469:Cell Separation; D003342:Corpus Striatum / Q000166:cytology / Q000502:physiology*; D004095:Dihydropyridines / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D005784:Gene Amplification; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010455:Peptides / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013111:Spider Venoms / Q000494:pharmacology; D013997:Time Factors; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D004095:Dihydropyridines; D010455:Peptides; D012333:RNA, Messenger; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA; D002118:Calcium