Hyperpolarization-activated inward current in neurons of the rat's dorsal nucleus of the lateral lemniscus in vitro.
Hyperpolarization-activated inward current in neurons of the rat's dorsal nucleus of the lateral lemniscus in vitro. J. Neurophysiol. 78: 2235-2245, 1997. The hyperpolarization-activated current (Ih) underlying inward rectification in neurons of the rat's dorsal nucleus of the lateral lemniscus (DNLL) was investigated using whole cell patch-clamp techniques. Patch recordings were made from DNLL neurons of young rats (21-30 days old) in 400 micro;m tissue slices. Under current clamp, injection of negative current produced a graded hyperpolarization of the cell membrane, often with a gradual sag in the membrane potential toward the resting value. The rate and magnitude of the sag depended on the amount of hyperpolarizing current. Larger current resulted in a larger and faster decay of the voltage. Under voltage clamp, hyperpolarizing voltage steps elicited a slowly activating inward current that was presumably responsible for the sag observed in the voltage response to a steady hyperpolarizing current recorded under current clamp. Activation of the inward current (Ih) was voltage and time dependent. The current just was seen at a membrane potential of -70 mV and was activated fully at -140 mV. The voltage value of half-maximal activation of Ih was -78.0 +/- 6.0 (SE) mV. The rate of Ih activation was best approximated by a single exponential function with a time constant that was voltage dependent, ranging from 276 +/- 27 ms at -100 mV to 186 +/- 11 ms at -140 mV. Reversal potential (Eh) of Ih current was more positive than the resting potential. Raising the extracellular potassium concentration shifted Eh to a more depolarized value, whereas lowering the extracellular sodium concentration shifted Eh in a more negative direction. Ih was sensitive to extracellular cesium but relatively insensitive to extracellular barium. The current amplitude near maximal-activation (about -140 mV) was reduced to 40% of control by 1 mM cesium but was reduced to only 71% of control by 2 mM barium. When the membrane potential was near the resting potential (about -60 mV), cesium had no effect on the membrane potential, current-evoked firing rate and input resistance but reduced the spontaneous firing. When the membrane potential was more negative than -70 mV, cesium hyperpolarized the cell, decreased current-evoked firing and increased the input resistance. Ih in DNLL neurons does not contribute to the normal resting potential but may enhance the extent of excitation, thereby making the DNLL a consistently powerful inhibitory source to upper levels of the auditory system.
Fu
X W
XW
Laboratory of Sensory Neuroscience, Institute of Neuroscience, Carleton University, Ottawa, Ontario K1S 5B6, Canada.
Brezden
B L
BL
Wu
S H
SH
D000818:Animals; D001306:Auditory Pathways / Q000502:physiology*; D017609:Barium Compounds / Q000494:pharmacology; D002586:Cesium / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects; D066298:In Vitro Techniques; D007245:Inferior Colliculi / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000494:pharmacology
D017609:Barium Compounds; D002712:Chlorides; C024986:barium chloride; D002586:Cesium; D012964:Sodium; C028019:cesium chloride; D011188:Potassium