A whole cell patch-clamp study on the pacemaker potential in dopaminergic neurons of rat substantia nigra compacta.
A whole-cell patch-clamp recording was obtained from dopamine (DA) neurons (n = 68) in the substantia nigra compacta (SNc) in in vitro slice preparations in order to study the underlying current for pacemaker-like slow depolarization (PLSD) which was considered as a basis for rhythmic firing of DA neurons. SNc DA neurons were identified immunohistochemically after recording. Results demonstrated that: (1) Under current clamped condition in the presence of TTX, DA neurons (n = 5) displayed the oscillation of membrane potential with high threshold spikes. An application of a hyperpolarizing and depolarizing current pulse (at the membrane potential where oscillation was no longer seen) induced a prominent anomalous rectification and pacemaker-like slow depolarization (PLSD), respectively. (2) Under voltage-clamped conditions in the presence of TTX, a command pulse positive to -50 mV from a holding potential of -80 mV induced a persistent Ca2+ current which was usually preceded by either a transient K+ (n = 7) or a transient Ca2+ (n = 4) current recorded with a patch pipette containing potassium gluconate (145 mM). (3) When outward currents were suppressed by 140 mM CsCl and 10 mM EGTA intercellularly applied through the patch pipette, a command pulse positive to -50 to -40 mV induced either a persistent Ca2+ current alone (n = 4) or a persistent Ca2+ current preceded by a transient Ca2+ current (n = 11). (4) The threshold for activation of the persistent Ca2+ current (Ip) was around -60 to -55 mV. The amplitude of Ip produced by a command pulse stepped to -50 mV from a holding potential of -80 mV was -78 +/- 42 pA (n = 23). (5) The threshold for activation of transient Ca2+ current (IT) was around -70 to -65 mV and inactivated completely at -70 to -65 mV (n = 11). The peak amplitude of IT evoked at -60 to -55 mV from a holding potential of more negative than -80 mV was 489 +/- 170 pA (n = 11). (6) The decay time constant of IT was 28 +/- 12 ms at -60 mV (n = 8) and that of IP was 2.35 +/- 1.37 s at -50 mV (n = 11) when recorded with a pipette containing 10 mM EGTA and 140 mM CsCl. (7) The decay of IP was apparently accelerated by decreasing the concentration of EGTA in the pipette solution from 10 to 1 mM.(ABSTRACT TRUNCATED AT 400 WORDS)
Kang
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Department of Anatomy and Neurobiology, College of Medicine, University of Tennessee, Memphis 38163.
Kitai
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D000669:Amplifiers, Electronic; D000818:Animals; D001683:Biological Clocks / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D004298:Dopamine / Q000502:physiology*; D004594:Electrophysiology; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007546:Isoquinolines; D007700:Kinetics; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013378:Substantia Nigra / Q000166:cytology / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D007546:Isoquinolines; D013779:Tetrodotoxin; C017475:lucifer yellow; D004298:Dopamine