Involvement of R-type Ca2+ channels in neurotransmitter release from spinal dorsolateral funiculus terminals synapsing motoneurons.
Molecular studies have revealed the presence of R-type voltage-gated Ca(2+) channels at pre- and postsynaptic regions; however, no evidence for the participation of these channels in transmitter release has been presented for the spinal cord. Here we characterize the effects of SNX-482, a selective R channel blocker, on the monosynaptic excitatory postsynaptic potentials (EPSPs) evoked in motoneurons by stimulation of dorsolateral funiculus (DLF) terminals in a slice preparation from the adult turtle spinal cord. SNX-482 inhibited neurotransmission in a dose-dependent manner, with an IC(50) of approximately 9 +/- 1 nM. The EPSP time course and membrane time constant of the motoneurons were not altered, suggesting a presynaptic mechanism. The toxin inhibited the residual component of the EPSPs recorded in the presence of N- and P/Q-type Ca(2+) channel blockers, strongly suggesting a role for the R channels in neurotransmission at the spinal cord DLF terminals. Consistently with this, RT-PCR analysis of turtle spinal cord segments revealed the expression of the Ca(V)2.3 pore-forming (alpha(1E)) subunit of R channels, whereas the use of anti-alpha(1E)-specific antibodies resulted in its localization in the DLF fibers as demonstrated by immunohistochemistry coupled with laser confocal microscopy.
Castro
Alberto
A
Department of Physiology, Biophysics and Neuroscience, Center for Research and Advanced Studies of the National Polytechnic Institute (Cinvestav-IPN), Mexico City, CP 07300, Mexico.
Andrade
Arturo
A
Vergara
Paula
P
Segovia
Jose
J
Aguilar
Justo
J
Felix
Ricardo
R
Delgado-Lezama
Rodolfo
R
D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D002121:Calcium Channel Blockers / Q000008:administration & dosage / Q000494:pharmacology*; D020908:Calcium Channels, R-Type / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects / Q000502:physiology*; D007150:Immunohistochemistry; D018613:Microscopy, Confocal; D009046:Motor Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013111:Spider Venoms / Q000008:administration & dosage / Q000494:pharmacology*; D013116:Spinal Cord / Q000033:anatomy & histology / Q000166:cytology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D014426:Turtles
D002121:Calcium Channel Blockers; D020908:Calcium Channels, R-Type; C115521:SNX 482; D013111:Spider Venoms