Properties of the hyperpolarization-activated cation current Ih in rat midbrain dopaminergic neurons.
Intracellular electrophysiological recordings in current- and voltage-clamp mode were obtained from dopaminergic neurons of the rat mesencephalon in an in vitro slice preparation. In current-clamp mode, a time-dependent anomalous rectification (TDR) of the membrane was observed in response to hyperpolarizing current pulses. In single-electrode voltage-clamp mode, a slowly developing inward current (Ih) underlying the TDR was studied by hyperpolarizing voltage commands from a holding potential of -50 to -60 mV. Ih started to be activated at approximately -69 mV, was fully activated at -129 to -141 mV, with half-maximal activation at -87 mV, and showed no inactivation with time. The time course of development of Ih followed a single exponential, and its time constant was voltage-dependent. At -81 mV, Ih activated with a time constant of 379 +/- 47.6 ms, whereas at -129 mV Ih activated with a time constant of 65 +/- 2.2 ms. Its estimated reversal potential was -35 +/- 4 mV. Raising the extracellular concentration of K+ from 2.5 to 6.5 and to 12.5 mM increased the amplitude of Ih while reducing the extracellular concentration of Na+ from 153.2 to 27.2 mM caused a reduction in amplitude of Ih. Bath application of caesium (1-5 mM) reversibly reduced or blocked the TDR/Ih. Perfusion of tetrodotoxin (0.5-1 microM), tetraethylammonium (10-20 mM) or barium (0.3-2 mM) did not significantly affect Ih. Ih was also present in cells impaled with CsCl-filled electrodes.(ABSTRACT TRUNCATED AT 250 WORDS)
Mercuri
N B
NB
Clinica Neurologica, University of Tor Vergata-Rome, Italy.
Bonci
A
A
Calabresi
P
P
Stefani
A
A
Bernardi
G
G
D000818:Animals; D002412:Cations / Q000378:metabolism*; D002586:Cesium / Q000494:pharmacology; D004298:Dopamine / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology; D005110:Extracellular Space; D005260:Female; D007477:Ions; D008297:Male; D008636:Mesencephalon / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D002412:Cations; D007477:Ions; D002586:Cesium; D004298:Dopamine