The Journal of Neurophysiology Vol. 86 No. 3 September 2001, pp. 1156-1163
Copyright ©2001 by the American Physiological Society

E_f-Current Contributes to Whole-Cell Calcium Current in Low Calcium in Frog Sympathetic Neurons

Department of Physiology, Tulane University Health Science Center, New Orleans, Louisiana 70112

Liang, Haoya and Keith S. Elmslie. E_f-Current Contributes to Whole-Cell Calcium Current in Low Calcium in Frog Sympathetic Neurons. J. Neurophysiol. 86: 1156-1163, 2001. Because Ca²⁺ plays diverse roles in intracellular signaling in neurons, several types of calcium channels are employed to control Ca²⁺ influx in these cells. Our experiments focus on resolving the paradox of why whole-cell current has not been observed under typical recording conditions for one type of calcium channel that is highly expressed in frog sympathetic neurons. These channels, referred to as E_f-channels, are present in the membrane at a density greater than the channels that carry ~90% of whole-cell current in low Ba²⁺; but, E_f-current has not been detected in low Ba²⁺. Using Ca²⁺ instead of Ba²⁺ as the charge carrier, we recorded a possible E-type current in frog sympathetic neurons. The current was resistant to specific blockers of N-, L-, and P/Q-type calcium channels but was more sensitive to Ni²⁺ block than was N- or L-current. Current amplitude in Ca²⁺ is slightly greater than that in Ba²⁺. In 3 mM Ca²⁺, the current contributed ~12% of total current at peak voltage and increased at voltages more hyperpolarized to the peak, reaching ~40% at 30 mV, where whole-cell current starts to activate. The presence of E_f-current in 3 mM Ca²⁺ suggests a potential role for E_f-channels in regulating calcium influx into sympathetic neurons.