Noradrenaline inhibits exocytosis via the G protein βγ subunit and refilling of the readily releasable granule pool via the α(i1/2) subunit.
The molecular mechanisms responsible for the 'distal' effect by which noradrenaline (NA) blocks exocytosis in the β-cell were examined by whole-cell and cell-attached patch clamp capacitance measurements in INS 832/13 β-cells. NA inhibited Ca(2+)-evoked exocytosis by reducing the number of exocytotic events, without modifying vesicle size. Fusion pore properties also were unaffected. NA-induced inhibition of exocytosis was abolished by a high level of Ca(2+) influx, by intracellular application of antibodies against the G protein subunit Gβ and was mimicked by the myristoylated βγ-binding/activating peptide mSIRK. NA-induced inhibition was also abolished by treatment with BoNT/A, which cleaves the C-terminal nine amino acids of SNAP-25, and also by a SNAP-25 C-terminal-blocking peptide containing the BoNT/A cleavage site. These data indicate that inhibition of exocytosis by NA is downstream of increased [Ca(2+)](i) and is mediated by an interaction between Gβγ and the C-terminus of SNAP-25, as is the case for inhibition of neurotransmitter release. Remarkably, in the course of this work, a novel effect of NA was discovered. NA induced a marked retardation of the rate of refilling of the readily releasable pool (RRP) of secretory granules. This retardation was specifically abolished by a Gα(i1/2) blocking peptide demonstrating that the effect is mediated via activation of Gα(i1) and/or Gα(i2).
Zhao
Ying
Y
Department of Molecular Medicine, Cornell University, Ithaca, NY 14853-6401, USA.
Fang
Qinghua
Q
Straub
Susanne G
SG
Lindau
Manfred
M
Sharp
Geoffrey W G
GW
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D005089:Exocytosis / Q000502:physiology*; D044385:GTP-Binding Protein alpha Subunits / Q000235:genetics / Q000378:metabolism*; D044387:GTP-Binding Protein beta Subunits / Q000378:metabolism*; D005786:Gene Expression Regulation; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000502:physiology; D009638:Norepinephrine / Q000502:physiology*; D050825:Synaptosomal-Associated Protein 25 / Q000235:genetics / Q000378:metabolism
D044385:GTP-Binding Protein alpha Subunits; D044387:GTP-Binding Protein beta Subunits; D007328:Insulin; D050825:Synaptosomal-Associated Protein 25; D002118:Calcium; D009638:Norepinephrine