Caerulein causes translocation of protein kinase C in rat acini without increasing cytosolic free Ca2+.
We investigated the relationships between changes in cytosolic free Ca2+ ([Ca2+]i) and amylase secretion in dispersed rat pancreatic acini. Although 10 pM caerulein did not raise [Ca2+]i, higher concentrations (1 nM) of the peptide elicited a prompt, marked, but transient (2-3 min) elevation of [Ca2+]i. Both concentrations of caerulein caused an almost identical release of amylase over a 30-min period. To investigate the mechanism(s) underlying Ca2+-independent secretion, we measured the effect of the secretagogue on protein kinase C activity and found that both caerulein concentrations caused a significant translocation of protein kinase C from the cytosolic to the microsomal fraction. Because 1 nM caerulein induced a greater enzyme secretion than 10 pM caerulein during the first 2-5 min of stimulation, we explored further the role of [Ca2+]i transients during the first minutes of secretion. Addition of ionomycin in the presence of 10 pM caerulein resulted in a rise in [Ca2+]i and enhanced secretion as a result of caerulein in a near additive fashion during the first 2 min of stimulation. Second, we pretreated acini for 5 min with 1 microM 12-O-tetradecanoylphorbol-13-acetate. This maneuver inhibited both caerulein-induced inositol trisphosphate formation and [Ca2+]i elevation. These findings were paralleled by a similar inhibition of caerulein-stimulated amylase release only during the first 5 min of secretion. These results indicate that 1) caerulein can stimulate amylase secretion independently of a concomitant [Ca2+]i rise, possibly by activation of protein kinase C, and 2) an elevation of [Ca2+]i serves as a trigger to enhance amylase release only during the initial phase of secretion.
Bruzzone
R
R
Institut de Biochimie Clinique, University of Geneva, Switzerland.
Regazzi
R
R
Wollheim
C B
CB
D000681:Amylases / Q000378:metabolism; D000818:Animals; D001572:Benzofurans; D002118:Calcium / Q000378:metabolism*; D002108:Ceruletide / Q000494:pharmacology*; D016257:Fura-2; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000378:metabolism; D008297:Male; D010179:Pancreas / Q000187:drug effects / Q000201:enzymology*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D001572:Benzofurans; D007295:Inositol Phosphates; D015544:Inositol 1,4,5-Trisphosphate; D002108:Ceruletide; D011493:Protein Kinase C; D000681:Amylases; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D016257:Fura-2