CALCIUM BUFFERING PROPERTIES OF CALBINDIN-D(28K) AND PARVALBUMIN IN RAT SENSORY NEURONS

1. We have examined the ability of the Ca2+-binding proteins (CABP) ca lbindin D28k and parvalbumin to modulate increases in the intracellula r free Ca2+ concentration ([Ca2+]i), produced by brief depolarizations , in rat dorsal root ganglion (DRG) neurones. 2. In order to obtain go od voltage control, we replated DRG neurones prior to performing these experiments. Immunocytochemical staining of these cells revealed that approximately 10 % stained for CABPs. 3. Using fluorescently labelled parvalbumin, we demonstrated that in the whole-cell voltage clamp mod e the protein freely entered the cell soma with a mean half-life t0.5 of 6 min 22 s +/- 54 s. 4. Analysis of the effects of calbindin D28k ( 370 muM) and parvalbumin (1 mm) on Ca2+ currents in the whole-cell vol tage clamp mode, revealed that neither protein changed the rate of ina ctivation of the Ca2+ current or its rate of run-down. 5. Introducing either calbindin D28k (370 muM) or parvalbumin (1 mm) into the cell so ma did not significantly alter the basal [Ca2+]i when compared to cont rol cells. 6. Compared to control cells, both CABPs significantly redu ced the peak [Ca2+] obtained for a Ca2+ influx of an equivalent charge density, whereas lysozyme (1 mm), a protein with low affinity for Ca2 +, failed to do so. 7. Calbindin D28k caused an 8-fold decrease in the rate of rise in [Ca2+]i and altered the kinetics of decay of [Ca2+]i to a single slow component. Parvalbumin also slowed the rate of rise i n [Ca2+]i. Parvalbumin selectively increased a fast component in the d ecay of the Ca2+ signal. 8. These data demonstrate that both calbindin D28k and parvalbumin effectively buffer Ca2+ in a cellular environmen t and way therefore regulate Ca2+-dependent aspects of neuronal functi on.