Pb2 + modulates ryanodine receptors from the endoplasmic reticulum in rat brain

Abstract

Although the neurotoxic mechanism of lead (Pb2+) has been extensively studied, it is not well understood. The effects of Pb2+ on free cytosolic calcium (Ca2+) concentration and calcium-regulated events have been suggested to be major mechanisms in Pb2+ toxicity. Based on our previous findings that Pb2+ changes calcium release through ryanodine receptors (RyRs), the modulation of endoplasmic reticulum (ER) vesicular RyRs by Pb2+ was investigated further in the present study. The results of [3H]ryanodine binding assays showed that in the presence of a free Ca2+ concentration ([Ca2+]f) of 100μM, Pb2+ modulated the equilibrium of [3H]ryanodine binding to brain RyRs, with a U-type dose-response curve, where minimal binding was observed at a free Pb2+ concentration ([Pb2+]f) of 0.39μM. This modulation was also observed over a time course. Scatchard analysis indicated that both an increase in Kd and a possible decrease in Bmax were responsible for the decrease in binding induced by low [Pb2+]f. Moreover, the effects of Pb2+ on the function of ER RyRs in neurons might also be controlled by other RyR modulators. Whole-cell patch-clamp experiments revealed that dynamic calcium oscillations evoked by specific RyR agonists were depressed rapidly and reversibly by exposure to 10μM Pb2+. Our study indicates that RyRs are molecular targets of Pb2+, and this interaction disturbs Ca2+ signals and leads to neurotoxicity.