Three novel types of voltage-dependent calcium channels in rat cerebellar neurons.
With the aim of characterizing the functional and pharmacological properties of the different voltage-dependent Ca2+ channels expressed in a given type of CNS neuron, we obtained single Ca2+ channel recordings from rat cerebellar granule cells in primary culture. Our data show that three novel classes of voltage-dependent Ca2+ channels are coexpressed in cerebellar granule cells. They are pharmacologically distinct from dihydropyridine-sensitive L-type and omega-conotoxin-sensitive N-type channels, and their functional properties are different from those of P- and T-type channels. The three novel 21 pS G1-, 15 pS G2-, and 20 pS G3-type Ca2+ channels have similar inactivation properties. They show complete steady-state inactivation at -40 mV and their single-channel average currents have both sustained and decaying components. They differ in activation threshold (-40 mV for G2, -30 mV for G3, and -10 mV for G1, with 90 mM Ba2+ as charge carrier), mean open time (1.2 msec for G2, 1 msec for G3, 0.8 msec for G1), and single-channel currents (at 0 mV: 0.5 pA for G2, 0.8 pA for G3, and 1.4 pA for G1). Together with the previously characterized multiple L-type Ca2+ channels (Forti and Pietrobon, 1993), G1-, G2-, and G3-type channels constitute the large majority of Ca2+ channels of cerebellar granule cells in culture. The low activation threshold of G2-type channels and their inactivation properties suggest that they might be native counterparts of the recently expressed rat brain clone rbE-II (Soong et al., 1993).
Forti
L
L
Department of Biomedical Sciences, University of Padova, Italy.
Tottene
A
A
Moretti
A
A
Pietrobon
D
D
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D004095:Dihydropyridines / Q000494:pharmacology; D004594:Electrophysiology; D009474:Neurons / Q000378:metabolism*; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004095:Dihydropyridines; D010455:Peptides; D020866:omega-Conotoxin GVIA