Differential roles of two types of voltage-gated Ca2+ channels in the dendrites of rat cerebellar Purkinje neurons.
The distribution and function of voltage-gated Ca2+ channels in Purkinje neurons in rat cerebellar slices were studied using simultaneous Ca2+ imaging and whole-cell patch clamp recording techniques. Voltage-gated Ca2+ channels were activated by applying depolarizing voltage steps through the pipette attached at the soma in a voltage-clamp mode in the presence of tetrodotoxin. Poor space clamp due to extensive arborization of the dendrites allowed the dendrites to fire Ca2+ spikes. Ca2+ imaging with Fura-2 injected through the pipette, showed a steady [Ca2+]i increase at the soma and transient, spike-linked [Ca2+]i jumps in the dendrites. omega-Agatoxin-IVA (200 nM) abolished the depolarization-induced Ca2+ spikes, the spike-linked [Ca2+]i increase in the dendrites, and the steady [Ca2+]i increase at the soma. omega-Conotoxin-GVIA (5 microM) and nifedipine (3 microM) had no significant effect on the depolarization-induced responses. In the presence of 4-aminopyridine(2 mM) and omega-Agatoxin-IVA, transient [Ca2+]i increases remained in the dendrites. Low concentrations of Ni2+(100 microM) reversibly suppressed this [Ca2+]i increase. The voltage for half-maximal activation and inactivation of this component were lower than -50 mV and -31 mV, respectively. In normal conditions, low concentration of Ni2+ slowed the onset of the Ca2+ spike without changing the time course of the spikes or the amplitude of the accompanying [Ca2+]i increase. These results show that omega-Agatoxin-IVA-sensitive Ca2+ channels are distributed both in the soma and the dendrites, and are responsible for dendritic Ca2+ spikes, whereas low-voltage activated, Ni2+-sensitive Ca2+ channels are distributed in the whole dendrites including both thick and fine branches, and provide boosting current for spike generation.
Watanabe
S
S
Faculty of Pharmaceutical Sciences, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan.
Takagi
H
H
Miyasho
T
T
Inoue
M
M
Kirino
Y
Y
Kudo
Y
Y
Miyakawa
H
H
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D003712:Dendrites / Q000187:drug effects / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008978:Mollusk Venoms / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D011689:Purkinje Cells / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar; D013111:Spider Venoms / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D008978:Mollusk Venoms; D010455:Peptides; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D013779:Tetrodotoxin; D020866:omega-Conotoxin GVIA