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J Neurophysiol 81: 95-102, 1999;
0022-3077/99 $5.00
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The Journal of Neurophysiology Vol. 81 No. 1 January 1999, pp. 95-102
Copyright ©1999 The American Physiological Society

Potassium Currents in Precursor Cells Isolated From the Anterior Subventricular Zone of the Neonatal Rat Forebrain

R. R. Stewart1, T. Zigova2, and M. B. Luskin2

1 Laboratory of Molecular and Cellular Neurobiology, National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland 20892-8115; and 2 Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322-3030

Stewart, R. R., T. Zigova, and M. B. Luskin. Potassium currents in precursor cells isolated from the anterior subventricular zone of the neonatal rat forebrain. J. Neurophysiol. 81: 95-102, 1999. The progenitor cells from the anterior part of the neonatal subventricular zone, the SVZa, are unusual in that, although they undergo division, they have a neuronal phenotype. To characterize the electrophysiological properties of the SVZa precursor cells, recordings were made of potassium and sodium currents from SVZa cells that were removed from postnatal day 0-1 rats and cultured for 1 day. The properties of the delayed rectifier and A-type potassium currents were described by classical Hodgkin and Huxley analyses of activation and inactivation. In addition, cells were assessed under current clamp for their ability to generate action potentials. The A-type potassium current (IK(A)) was completely inactivated at a holding potential of -50 mV. The remaining potassium current resembled the delayed rectifier current (IK(DR)) in that it was blocked by tetraethylammonium (TEA; IC50 4.1 mM) and activated and inactivated slowly compared with IK(A). The conductance-voltage (G-V) curve revealed that G increased continuously from 0.2 nS at -40 mV to a peak of 2.6 nS at +10 or +20 mV, and then decreased for voltages above +30 mV. Activation time constants were largest at -40 mV (~11 ms) and smallest at 100 mV (~1.5 ms). The properties of IK(A) were studied in the presence of 20 mM TEA, to block IK(DR), and from a holding potential of -15 mV, to inactivate both IK(DR) and IK(A). IK(A) was then allowed to recover from inactivation to negative potentials during 200- to 800-ms pulses. Recovery from inactivation was fastest at -130 mV (~21 ms) and slowest at -90 mV (~135 ms). Inactivation was voltage independent from -60 to +60 mV with a time constant of ~15 ms. At steady state, IK(A) was half inactivated at -90 mV. GK(A) increased from 0.2 nS at -60 mV to a peak of 2.4 nS at +40 mV. Finally, the activation time constants ranged from ~1.9 ms at -50 mV to 0.7 ms at +60 mV. The properties of IK(A) resembled those of IK(A) found in differentiating cerebellar granule neurons. Most SVZa cells had sodium currents (28/32 cells). However, in current clamp 11 of 12 cells were incapable of generating action potentials from voltages of -30 to -100 mV, suggesting that the available current densities were too low to support excitability.




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