Intracellular Ca2+ was measured in freshly dissociated mouse dorsal root ganglion neurons by using Fluo3 as fluorescent Ca2+ probe. Short perifusions (5-10 s) with 30 mM K+ induced a sharp rise in fluorescence due to the entry of Ca2+ ions, in particular through L and N voltage sensitive Ca2+ channels opened by the action potentials that were triggered by depolarization. Perifusions with 1 or 10 nM (1DMe)Y8Fa (DYL(NMe)FQPQRFamide), a neuropeptide FF analog, suppressed the rise in fluorescence induced by short (5-10 s) K+ perifusions within 30 min. However, when K+ perifusions of longer duration were applied, Fluo3 fluorescence rose after an increased latency. Two other analogs, (2DMe)Y8Fa (DYDL(NMe)FQPQRFamide) and (3D)Y8Fa (DYDLDFQPQRFamide), had the same effect; similarly neuropeptide FF (FLFQPQRFamide, 1 nM, 30 min) reduced intracellular Ca2+ rise during depolarization. These features indicate that neuropeptide FF and its analogs exert their pharmacological effects by reducing the [Ca2+]i transient induced by short depolarizations.