Effect of low external calcium on the ERG current of NG108-15 cells.
K(+) currents through ERG (ether-à-go-go related gene) channels were recorded in whole-cell voltage clamped NG108-15 neuroblastomaxglioma hybrid cells. The channels were fully activated by low holding potential (V(H)=-20 mV) and long depolarizing prepulses. Hyperpolarizing pulses elicited inward currents which deactivated after reaching a peak. Lowering [Ca(2+)](o) from 5 to 1. 5 or 0.5 mM decreased tau(-1), the rate constant of deactivation. The effect can be explained by a shift of the tau(-1)(V) curve to more negative potentials caused by an increase in surface charge density. Plotting tau(-1) against [Ca(2+)](o) for different potentials yielded straight lines; their slope was independent of potential at -140 to -120 mV and decreased at more positive potentials. The time to peak curve and the maximum of the steady-state inward current were also shifted to more negative potentials. In addition, peak ERG inward current increased. Raising [Ca(2+)](o) from 5 to 10 mM accelerated deactivation and decreased the peak current. 5 mM Ba(2+) affected tau(-1) similarly and inhibited peak current more strongly whereas 5 mM Mg(2+) was less potent. As found by Faravelli et al. (J. Physiol. 496 (1996) 13), bath solutions devoid of divalent cations (0 Ca(2+), 0 Mg(2+), 0.1 or 1.1 mM EGTA) abolished deactivation almost completely. The phenomenon was seen with bath containing either 40 or 6.5 mM K(+). Its occurrence was favored by raising the temperature to 34 degrees C. It suggests a particular requirement of channel closing for Ca(2+).
Meves
H
H
I. Physiologisches Institut der Universität des Saarlandes, D-66421, Homburg-Saar, Germany. phmev@med-rz.uni-sb.de
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D000072237:ERG1 Potassium Channel; D004533:Egtazic Acid; D051638:Ether-A-Go-Go Potassium Channels; D006822:Hybrid Cells; D015640:Ion Channel Gating; D051379:Mice; D018408:Patch-Clamp Techniques; D011188:Potassium; D015221:Potassium Channels / Q000737:chemistry*; D024642:Potassium Channels, Voltage-Gated; D011199:Potentiometry; D051381:Rats; D013696:Temperature; D014407:Tumor Cells, Cultured
D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606915:Kcnh2 protein, mouse; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D001464:Barium; D004533:Egtazic Acid; D011188:Potassium; D002118:Calcium