Inhibition of RabSB expression attenuates Ca2+-dependent exocytosis in rat anterior pituitary cells

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Abstract
LOW-MOLECULAR-WEIGHT GTP-binding proteins (small G proteins) of the Rab family have been proposed to act as central regulators of vesicular traffic1,2, and proteins of the Rab3 subfamily (Rab3A, B, C and D)3–6 are thought to be associated with membrane vesicles or granules undergoing exocytotic fusion with the plasma membrane7–10. Rab3A is highly expressed in brain11, whereas Rab3B is the major form found in rat anterior pituitary gland. We report here that antisense oligonucleotides against Rab3B, introduced into pituitary cells using the whole-cell patch clamp technique, specifically and reversibly block expression of Rab3B. We find that calcium-dependent exocytosis is inhibited without affecting endocytosis. Antisense oligonucleotides directed against Rab3A have no effect. Our results indicate that Rab3B is likely to be a key intracellular signalling molecule which can control exocytosis downstream of other calcium-dependent processes in anterior pituitary cells.