Characterization in Effective Stimulation on the Magnitude, Gating, Frequency Dependence, and Hysteresis of I(Na) Exerted by Picaridin (or Icaridin), a Known Insect Repellent

Picaridin (icaridin), a member of the piperidine chemical family, is a broad-spectrum arthropod repellent. Its actions have been largely thought to be due to its interaction with odorant receptor proteins. However, to our knowledge, to what extent the presence of picaridin can modify the magnitude, gating, and/or the strength of voltage-dependent hysteresis (Hys((V))) of plasmalemmal ionic currents, such as, voltage-gated Na(+) current [I(Na)], has not been entirely explored. In GH(3) pituitary tumor cells, we demonstrated that with exposure to picaridin the transient (I(Na(T))) and late (I(Na(L))) components of voltage-gated Na(+) current (I(Na)) were differentially stimulated with effective EC(50)’s of 32.7 and 2.8 μM, respectively. Upon cell exposure to it, the steady-state current versus voltage relationship I(Na(T)) was shifted to more hyperpolarized potentials. Moreover, its presence caused a rightward shift in the midpoint for the steady-state inactivate curve of the current. The cumulative inhibition of I(Na(T)) induced during repetitive stimuli became retarded during its exposure. The recovery time course from the I(Na) block elicited, following the conditioning pulse stimulation, was satisfactorily fitted by two exponential processes. Moreover, the fast and slow time constants of recovery from the I(Na) block by the same conditioning protocol were noticeably increased in the presence of picaridin. However, the fraction in fast or slow component of recovery time course was, respectively, increased or decreased with an increase in picaridin concentrations. The Hys((V))’s strength of persistent I(Na) (I(Na(P))), responding to triangular ramp voltage, was also enhanced during cell exposure to picaridin. The magnitude of resurgent I(Na) (I(Na(R))) was raised in its presence. Picaritin-induced increases of I(Na(P)) or I(Na(R)) intrinsically in GH(3) cells could be attenuated by further addition of ranolazine. The predictions of molecular docking also disclosed that there are possible interactions of the picaridin molecule with the hNa(V)1.7 channel. Taken literally, the stimulation of I(Na) exerted by the exposure to picaridin is expected to exert impacts on the functional activities residing in electrically excitable cells.