Trans-ACPD, a metabotropic receptor agonist, produces calcium mobilization and an inward current in cultured cerebellar Purkinje neurons.
1. 1-aminocyclopentane-trans-1,3-dicarboxylic acid (t-ACPD), a racemic mixture of 1-aminocyclopentane-1S,3R-dicarboxylic acid and 1-aminocyclopentane-1R,3S-dicarboxylic acid, a selective agonist of the metabotropic glutamate receptor, was applied to mouse Purkinje neurons (PNs) in culture. Measurements of free intracellular Ca2+ were made using fura-2 microfluorimetric imaging and of membrane current using perforated-patch voltage-clamp recording in separate experiments. 2. Brief pulses of t-ACPD (< or = 100 microM, 1-5 s) consistently produced a large (200-600 nM) increase in dendritic Ca2+ that was sometimes followed by a somatic increase. The dendrites typically returned to basal Ca2+ levels within 10-30 s. 3. Ca2+ increases produced by t-ACPD were measured in Ca(2+)-free external saline [0.5 mM ethylene glycol-bis(beta-amino-ethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)], suggesting that they result from intracellular mobilization rather than influx. In addition, Ca2+ increases were not attenuated by a mixture of DL-AP5 and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) [antagonists of N-methyl-D-aspartate (NMDA) and AMPA/kainate receptors, respectively], but were almost entirely eliminated by L-AP3 (100 microM), a putative metabotropic receptor antagonist or by preincubation of the cultures in pertussis toxin. 4. Brief pulses of t-ACPD (10 microM) produced a small inward current that was associated with an increase in membrane conductance. This current was reversibly blocked by L-AP3 but not by treatments that attenuate some voltage-gated K+ currents. Thus this current is unlikely to underlie the depolarization that is produced by metabotropic agonists in hippocampal pyramidal cells by K(+)-channel closure. 5. The t-ACPD induced inward current was attenuated by substitution of external Na+ with Li+ or choline, or by application of the membrane-permeable Ca2+ chelator, bis-(2-aminophenoxy)-N,N,N',N'- tetraacetic acid (BAPTA)/AM. One mechanism that could mediate this current is electrogenic Nao/Cai exchange, triggered by Ca2+ mobilization.
Linden
D J
DJ
Roche Institute of Molecular Biology, Roche Research Center, Nutley, New Jersey 07110.
Smeyne
M
M
Connor
J A
JA
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects*; D002478:Cells, Cultured; D003515:Cycloleucine / Q000031:analogs & derivatives* / Q000494:pharmacology; D003592:Cytophotometry; D003712:Dendrites / Q000187:drug effects; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists; D005333:Fetus; D019204:GTP-Binding Proteins / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects; D051379:Mice; D009498:Neurotoxins / Q000494:pharmacology*; D011689:Purkinje Cells / Q000187:drug effects*; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects; D012964:Sodium / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects*
D015220:Calcium Channels; D018691:Excitatory Amino Acid Antagonists; D009498:Neurotoxins; D016194:Receptors, N-Methyl-D-Aspartate; D003515:Cycloleucine; C036361:1-amino-1,3-dicarboxycyclopentane; D012964:Sodium; D019204:GTP-Binding Proteins; D002118:Calcium