Sodium pump evokes high density pump currents in rat midbrain dopamine neurons.
1. Patch pipettes contained various concentrations of Na+ ([Na+]pip) in order to record strophanthidin-sensitive currents under voltage clamp in dopamine neurons in slices of rat substantia nigra and ventral tegmental area. 2. When [Na+]pip was 40 mM and the external K+ concentration ([K+]o) was 2.5 mM, strophanthidin (10 microM) evoked 461 +/- 121 pA of inward current. This effect was concentration dependent, with an EC50 of 7.1 +/- 2.6 microM. At potentials of -60 to -120 mV, strophanthidin-induced currents were not associated with significant changes in chord conductance. 3. Strophanthidin (10 microM) evoked 234 +/- 43 pA of inward current when [Na+]pip was 0.6 mM, and 513 +/- 77 pA when [Na+]pip was 80 mM. Despite higher pump currents with greater [Na+]pip, the strophanthidin EC50 was not significantly different for any of six different [Na+]pip. 4. Sodium pump currents were half-maximal when the [Na+]pip was about 1.3 mM. Maximum pump current was estimated at 830 pA (29 microA cm-2) at concentrations of intracellular Na+ that were assumed to be saturating (50-100 mM). 5. Strophanthidin currents were smaller in a reduced [K+]o (EC50 = 0.2 mM). 6. These data show that intracellular Na+ loading evokes relatively large pump currents. Our results are consistent with the physiological role of the sodium pump in burst firing in midbrain dopamine neurons
Shen
K Z
KZ
Departments of Physiology and Pharmacology, Oregon Health Sciences University, Portland, OR 97201, USA.
Johnson
S W
SW
D000818:Animals; D004298:Dopamine / Q000502:physiology*; D004558:Electric Stimulation; D004594:Electrophysiology; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D008636:Mesencephalon / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D009474:Neurons / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000502:physiology*; D013327:Strophanthidin / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013779:Tetrodotoxin; D013327:Strophanthidin; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D004298:Dopamine