Properties and functional implications of I (h) in hippocampal area CA3 interneurons

• Published in: Pflügers Archiv Vol. 462; no. 6; pp. 895 - 912
• Main Authors: Anderson, Warren D, Galván, Emilio J, Mauna, Jocelyn C, Thiels, Edda, Barrionuevo, Germán
• Format: Journal Article
• Language: English
• Published: Germany 01-12-2011
• Subjects: Animals; Computer Simulation; Cyclic Nucleotide-Gated Cation Channels - metabolism; gamma-Aminobutyric Acid - metabolism; Hippocampus - cytology; Hippocampus - physiology; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; Interneurons - physiology; Ion Channel Gating - physiology; Membrane Potentials - physiology; Patch-Clamp Techniques; Potassium Channels - metabolism; Protein Subunits - metabolism; Rats; Rats, Sprague-Dawley
• ISSN: 1432-2013
• DOI: 10.1007/s00424-011-1025-3

The present study examines the biophysical properties and functional implications of I (h) in hippocampal area CA3 interneurons with somata in strata radiatum and lacunosum-moleculare. Characterization studies showed a small maximum h-conductance (2.6 ± 0.3 nS, n = 11), shallow voltage dependence with a hyperpolarized half-maximal activation (V (1/2) = -91 mV), and kinetics characterized by double-exponential functions. The functional consequences of I (h) were examined with regard to temporal summation and impedance measurements. For temporal summation experiments, 5-pulse mossy fiber input trains were activated. Blocking I (h) with 50 μM ZD7288 resulted in an increase in temporal summation, suggesting that I (h) supports sensitivity of response amplitude to relative input timing. Impedance was assessed by applying sinusoidal current commands. From impedance measurements, we found that I (h) did not confer theta-band resonance, but flattened the impedance-frequency relations instead. Double immunolabeling for hyperpolarization-activated cyclic nucleotide-gated proteins and glutamate decarboxylase 67 suggests that all four subunits are present in GABAergic interneurons from the strata considered for electrophysiological studies. Finally, a model of I (h) was employed in computational analyses to confirm and elaborate upon the contributions of I (h) to impedance and temporal summation.