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
Departments of Physiology and Pharmacology, Oregon Health Sciences University, Portland, OR 97201, USA.
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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