Bradykinin-induced modulation of calcium signals in rat dorsal root ganglion neurons in vitro

We used combined patch-clamp-microfluorimetric recordings to examine the effects of bradykinin on [Ca²⁺]_i transients and the Ca²⁺ current (I_Ca) in rat dorsal root ganglion neurons in vitro. Bradykinin increased [Ca²⁺]_i in approximately 20% of dorsal root ganglion cells examined and inhibited the I_Ca in approximately 65% of dorsal root ganglion cells. Bradykinin also inhibited the I_Ca. when [Ca²⁺]_i was buffered with 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid or when Ba²⁺ was the charge carrier. When I_Ca's of increasing duration were elicited in these neurons, [Ca²⁺]_i transients were produced that increased in amplitude but eventually approached an asymptote at longer voltage steps. Similarly, the amplitude of the [Ca²⁺]_i transient also approached an asymptote in current-clamp recordings when cells were induced to fire a large number of action potentials. The bradykinin-induced inhibition of the amplitude of the [Ca²⁺]_i transient was more pronounced at shorter voltage steps. At pulse durations that produced asymptotic [Ca²⁺]_i signals, bradykinin no longer decreased the amplitude of the rise in [Ca²⁺]_i, although it still reduced the I_Ca. In current-clamp recordings, bradykinin also reduced the [Ca²⁺]_i signal that accompanied the generation of action potentials, but again bradykinin was more effective for shorter spike trains. Bradykinin also depolarized the majority of neurons (65%). The reduction in [Ca²⁺]_i produced by bradykinin in sensory neurons may be an important factor contributing to bradykinin-induced excitation of primary sensory afferents.