REGULATION OF PANCREATIC EXOCRINE FUNCTION BY MANAGANESE

  • Korc, Murray, (PI)

Project: Research project

Description

The acinar cell of the exocrine pancreas synthesizes and secretes
approximately 20 digestive enzymes. Both dietary and hormonal factors
have been implicated in the regulation of the synthesis of these
enzymes. The mechanisms whereby this regulation is effected are not
known. Further, it is not clear whether pancreatic enzyme synthesis and
secretion are linked via intracellular feedback mechanisms, coupled to
respond to the same stimuli, or independently regulated. The divalent
cation manganese (Mn) exerts direct effects on pancreatic protein
synthesis in rat pancreatic acini, enhancing synthesis at low
concentrations, and inhibiting synthesis at high concentrations. Mn
also enhances pancreatic digestive enzyme release. Cholecystokinin
(CCK), a pancreatic secretagogue that mobilizes intracellular Ca2+ by
activating the phosphatidylinositol cascade, also exerts biphasic
effects on pancreatic protein synthesis. The actions of Mn on protein
synthesis, like the actions of CCK, are modulated by Ca2+ and are
greatly enhanced in diabetic rat acini. Further, Mn and CCK alter
protein phosphorylation and enhance Ca2+ efflux in the pancreatic acinar
cell. Inasmuch as the pancreas is rich in Mn, these observations
suggest that Mn may coordinate the coupling of pancreatic digestive
enzyme synthesis with enzyme secretion, and act as an intracellular
mediator that modulates acinar cell responsiveness to second messengers
and their effector pathways. This possibility is strengthened by our
recent observation that Mn-mediated phosphorylation of a cytosolic
substrate is calmodulin-dependent and hormonally regulated. To test the
hypothesis that Mn participates in the physiological regulation of
pancreatic exocrine function, the proposed studies will focus on two
aspects of Mn action. First, the effects of Mn on protein
phosphorylation in isolated rat pancreatic acini and in homogenates of
whole pancreas will be determined, in order to characterize the effects
of Mn on the activities of cytosolic and particulate kinases that are
endogenous to the exocrine pancreas. Specific substrates that are
phosphorylated in the presence of Mn will be identified. The actions of
any Mn-dependent kinase in the pancreatic acinar cell will be
characterized with respect to substrate specificity, and compared with
the effects of other divalent cations and with previously described
kinases. Polyclonal antibodies will be raised against a protein whose
phosphorylation by Mn is modulated by insulin and calmodulin in order to
study its developmental expression. These antibodies and the
appropriate synthetic oligonucleotides will be used to screen cDNA
libraries in order to isolate the cDNA corresponding to the mRNA coding
for the protein. Second, the importance of Mn in the regulation of
cellular Ca2+ homeostasis will be assessed by comparing its effects on
cellular calcium fluxes with its actions on phospholipid hydrolysis in
both basal and CCK-stimulated states, and by studying the actions of Mn
and CCK on a putative acinar cell calcium channel using the patch-clamp
technique.
StatusFinished
Effective start/end date4/1/848/31/92

Funding

  • National Institutes of Health: $138,796.00
  • National Institutes of Health
  • National Institutes of Health
  • National Institutes of Health

Fingerprint

Manganese
Cholecystokinin
Acinar Cells
Enzymes
Exocrine Pancreas
Pancreas
Proteins
Calmodulin
Phosphotransferases
Phosphorylation
Antibodies
Divalent Cations
Calcium Channels
Substrate Specificity
Phosphatidylinositols

ASJC

  • Medicine(all)