Elevation of intracellular Na+ induced by hyperpolarization at the dendrites of pyramidal neurones of mouse hippocampus.
1. Whole-cell recordings were made from CA1 pyramidal cells in mouse hippocampal slices with patch pipettes containing the sodium indicator dye SBFI (sodium binding benzofuran isophthalate). Using a high-speed imaging system, we investigated changes in intracellular sodium concentration, [Na+]i, in response to hyperpolarizing pulses applied to the soma. 2. In current-clamp recordings, we detected increases in [Na+]i during negative current injection. Hyperpolarization-induced [Na+]i elevation was more prominent in the middle apical dendrites than in the soma. 3. In the voltage-clamp mode, hyperpolarization induced rapid increases in [Na+]i at the apical dendrites that were significantly faster than those at the soma. The signals were not affected by bath application of 1 microM TTX, but were reduced by 5 mM CsCl. 4. Changes in membrane potential recorded from the apical dendrites in response to negative currents were significantly smaller than those recorded from the soma. In the presence of 5 mM CsCl, the I-V relationships measured at the soma and the dendrites became almost identical, indicating that CsCl-sensitive components are predominantly in the apical dendrites. 5. These results suggest that hyperpolarization-induced [Na+]i elevations reflect Na+ influx through the non-selective cation channel (Ih channel), and that this channel is distributed predominantly in the apical dendrites. The non-uniform Na+ influx may contribute to integrative functions of the dendrites.
Tsubokawa
H
H
Laboratory for Cellular Neurophysiology, Brain Science Institute, RIKEN, Wako, Saitama 351-0198, Japan. neuron@jichi.ac.jp
Miura
M
M
Kano
M
M
D000818:Animals; D001572:Benzofurans; D003712:Dendrites / Q000378:metabolism; D004988:Ethers, Cyclic; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D007424:Intracellular Fluid / Q000378:metabolism; D007473:Ion Channels / Q000378:metabolism; D017136:Ion Transport; D008564:Membrane Potentials; D051379:Mice; D008810:Mice, Inbred C57BL; D018408:Patch-Clamp Techniques; D017966:Pyramidal Cells / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D001572:Benzofurans; D004988:Ethers, Cyclic; D005456:Fluorescent Dyes; D007473:Ion Channels; C061665:sodium-binding benzofuran isophthalate; D012964:Sodium