Voltage-gated K⁺ (Kv) channels play a major role in regulating the excitability of mammalian hippocampal neurons. In these neurons Kv channels control neuronal spike properties and firing frequency, and modulate neurotransmitter release. Kv channels have been divided into four subfamilies, Kv1-Kv4, which differ in their primary structure, biophysical properties, and subcellular localization. The aims of the present study were to compare the spiking parameters of excitatory and inhibitory hippocampal interneurons and to examine the expression of some types of voltage-gated potassium channels on neuronal membranes. Regular spiking (RS) parameters were studied in inhibitory and excitatory hippocampal cultured neurons (prepared from hippocampi isolated from 1-day old humanely killed Wistar rats) using combined whole cell current and voltage clamp recordings to examine action potential waveforms and postsynaptic responses correspondingly. The experiments were carried out on 18- to 28-days-old cultured neurons. GABAergic neurons were identified by the presence of monosynaptic inhibitory currents in the postsynaptic cell in response to action potentials generated in the stimulated cell in the presence of the excitatory transmission blockers D_L-AP5 (20 μM) and DNQX (20 μM). Dentate gyrus granule cells (GCs) were chosen as examples of excitatory neurons. The electrical activity of GCs was studied in presence of inhibitory transmission blocker bicucculine (10 μM). The RS parameters (i.e. spike amplitude, after-hyperpolarization amplitude, depolarization slope, repolarization slope, spike frequency adaptation) of inhibitory and excitatory neurons were reliably distinguished (Student’s t test, P<0.05). The distribution of voltage-gated potassium channels (Kv1.2, Kv3.1 and Kv4.2) was determined by immunocytochemistry. It was shown that expression of Kv4.2 potassium channels can determine regular spiking phenotype (Birnbaum et al. 2004). We found that expression of Kv4.2 was detected only in excitatory interneurons. No Kv4.2-specific fluorescence was observed in inhibitory interneurons. Kv1.2 immunoreactivity was detected in both GCs and RS inhibitory interneurons. Excitatory RS interneurons belonged to one population of GCs and were immunopositive for somatostatin. Inhibitory RS interneurons were divided onto two groups (k-means algorithm for data clusterization) according to morphology and peptide expression. The first group of cells demonstrated good immunoreactivity to somatostatin and had a soma size ~27.9 μm and an average of 5.1 neurites (n=20). The second group did not stain for somatostatin and had a soma size ~17.3 μm and an average of 3.3 neurites (n=15). In conclusion, different mechanisms appear to be responsible for the maintenance of regular spiking electrical activity in these inhibitory and excitatory interneurons.