α1E subunits form the pore of three cerebellar R-type calcium channels with different pharmacological and permeation properties

R-type Ca2+ 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 Ca2+ currents with permeation and/or pharmacological properties different from those of recombinant Ca2+ channels containing alpha(1E) subunits have been described, and therefore the molecular nature of R-type Ca2+ channels remains not completely settled. Here, we show that the R-type Ca2+ current of rat cerebellar granule cells consists of two components inhibited with different affinity by the alpha(1E) selective antagonist SNX482 (IC50 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 Ca2+ than with Ba2+ as charge carrier, and it is highly sensitive to Ni2+ 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 Ba2+ than with Ca2+ as charge carrier, and it has a low sensitivity to Ni2+ 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.