Neuronal excitability can be regulated through modulation of voltage threshold (Vth). Previous studies suggested that this modulation could be mediated by modulation of transient sodium currents (I_T) and/or persistent inward current (PIC). Modulation of I_T and PIC through activation of protein kinase C (PKC) has previously been described as a mechanism controlling neuronal excitability. We investigated modulation of I_T and PIC by PKC in rat spinal ventral neurons. In whole-cell voltage clamp, activation of PKC by application of 1-oleoyl-2-acetyl-sn-glycerol (OAG, 10-30 µM) resulted in: (1) a reduction of I_T amplitude by 33% accompanied an increase in half-width and a decrease in the maximal rise and decay rates of the I_T; (2) a reduction of PIC amplitude by 49% with a depolarization of PIC onset by 4.5 mV. Activation of PKC caused varied effects on Vth for eliciting I_T, with an unchanged Vth or depolarized Vth being the most common effects. In current clamp recordings, PKC activation produced a small but significant depolarization (2.0 mV) of Vth for action potential generation with an increase in half-width and a decrease in amplitude and the maximal rise and decay rates of action potentials. Inclusion of PKC inhibitor (PKCI19-36; 10-30 µM) in the recording pipette could block the OAG effects on I_T and PIC. The ability of 5HT to hyperpolarize Vth was not altered by PKC activation or inhibition. This study demonstrates that activation of PKC decreases the excitability of spinal ventral neurons and that Vth can be modulated by multiple mechanisms.