alpha(1E) subunits form the pore of three cerebellar R-type calcium channels with different pharmacological and permeation properties.
R-type Ca(2+) channels cooperate with P/Q- and N-type channels to control neurotransmitter release at central synapses. The leading candidate as pore-forming subunit of R-type channels is the alpha(1E) subunit. However, R-type Ca(2+) currents with permeation and/or pharmacological properties different from those of recombinant Ca(2+) channels containing alpha(1E) subunits have been described, and therefore the molecular nature of R-type Ca(2+) channels remains not completely settled. Here, we show that the R-type Ca(2+) current of rat cerebellar granule cells consists of two components inhibited with different affinity by the alpha(1E) selective antagonist SNX482 (IC(50) values of 6 and 81 nM) and a third component resistant to SNX482. The SNX482-sensitive R-type current shows the unique permeation properties of recombinant alpha(1E) channels; it is larger with Ca(2+) than with Ba(2+) as charge carrier, and it is highly sensitive to Ni(2+) block and has a voltage-dependence of activation consistent with that of G2 channels with unitary conductance of 15 pS. On the other hand, the SNX482-resistant R-type current shows permeation properties similar to those of recombinant alpha(1A) and alpha(1B) channels; it is larger with Ba(2+) than with Ca(2+) as charge carrier(,) and it has a low sensitivity to Ni(2+) block and a voltage-dependence of activation consistent with that of G3 channels with unitary conductance of 20 pS. Gene-specific knock-down by antisense oligonucleotides demonstrates that the different cerebellar R-type channels are all encoded by the alpha(1E) gene, suggesting the existence of alpha(1E) isoforms with different pore properties.
Tottene
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A
Department of Biomedical Sciences, University of Padova, 35121 Padova, Italy.
Volsen
S
S
Pietrobon
D
D
D000818:Animals; D016375:Antisense Elements (Genetics); D001464:Barium / Q000493:pharmacokinetics; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000493:pharmacokinetics; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020864:Calcium Channels, N-Type / Q000235:genetics / Q000378:metabolism; D020908:Calcium Channels, R-Type / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure*; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression / Q000502:physiology; D009532:Nickel / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013111:Spider Venoms / Q000494:pharmacology*
D016375:Antisense Elements (Genetics); D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D020908:Calcium Channels, R-Type; D011994:Recombinant Proteins; C115521:SNX 482; D013111:Spider Venoms; D001464:Barium; D009532:Nickel; D002118:Calcium