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A-type K⁺ Current of Dopamine and GABA Neurons in the Ventral Tegmental Area

Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois

Submitted 14 December 2005; accepted in final form 10 April 2006

A-type K⁺ current (I_A) is a rapidly inactivating voltage-dependent potassium current which can regulate the frequency of action potential (AP) generation. Increased firing frequency of ventral tegmental area (VTA) neurons is associated with the reinforcing effects of some drugs of abuse like nicotine and ethanol. In the present study, we classified dopamine (DA) and GABA VTA neurons, and investigated I_A properties and the physiological role of I_A in these neurons using conventional whole cell current- and voltage-clamp recording. DA VTA neurons had a mean firing frequency of 3.5 Hz with a long AP duration. GABA VTA neurons had a mean firing frequency of 16.7 Hz with a short AP duration. For I_A properties, the voltage-dependence of steady-state I_A activation and inactivation was similar in DA and GABA VTA neurons. I_A inactivation was significantly faster and became faster at positive voltages in GABA neurons than DA neurons. Recovery from inactivation was significantly faster in DA neurons than GABA neurons. I_A current density at full recovery was significantly larger in DA neurons than GABA neurons. In DA and GABA VTA neurons, latency to the first AP after the recovery from membrane hyperpolarization (repolarization latency) was measured. Longer repolarization latency was accompanied by larger I_A current density in DA VTA neurons, compared with GABA VTA neurons. We suggest that I_A contributes more to the regulation of AP generation in DA VTA neurons than in GABA VTA neurons.

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