(-)-Baclofen-induced and constitutively active inwardly rectifying potassium conductances in cultured rat midbrain neurons.
Biophysical and pharmacological properties, and development of the (-)-baclofen-induced potassium (KBac) conductance and the constitutively active inwardly rectifying potassium (KIR) conductance were characterised using the patch-clamp technique in cultured embryonic rat midbrain neurons. KBac conductance was induced by (-)-baclofen acting on gamma-aminobutyric acid B (GABAB) receptors, and displayed a high degree of selectivity for potassium ions, an approximate square-root dependence of conductance on extracellular potassium concentration and strongly voltage-dependent activation. Ba2+ blocked the conductance in a voltage-independent manner, whereas Cs+ produced a voltage-dependent block. In the same preparation, the KIR conductance displayed biophysical properties indistinguishable from those of the KBac conductance. Block of KIR currents by Ba2+ was voltage independent (KI, 4 microM), whereas Cs+ produced a voltage-dependent block (KI, 370 microM at -100 mV, equivalent valence, z', 1.67). The KBac and KIR conductances additionally displayed a strikingly similar pattern of development in culture; the specific conductance (nS/pF) of both conductances increased two- to three-fold between the first and second week in vitro, and remained constant thereafter.
O'Callaghan
J F
JF
I. Physiologisches Institut der Universität Heidelberg, Im Neuenheimer Feld 326, D-69120 Heidelberg, Germany.
Jarolimek
W
W
Lewen
A
A
Misgeld
U
U
D000818:Animals; D001418:Baclofen / Q000494:pharmacology*; D001464:Barium / Q000494:pharmacology; D002478:Cells, Cultured; D002586:Cesium / Q000494:pharmacology; D004553:Electric Conductivity; D004594:Electrophysiology; D008636:Mesencephalon / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology*; D011188:Potassium / Q000037:antagonists & inhibitors / Q000502:physiology*; D051381:Rats; D013237:Stereoisomerism
D002586:Cesium; D001464:Barium; D001418:Baclofen; D011188:Potassium