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Multisite Interactions Between Pb 2+ and Protein Kinase C and Its Role in Norepinephrine Release from Bovine Adrenal Chromaffin Cells
Author(s) -
Tomsig Jose L.,
Suszkiw Janusz B.
Publication year - 1995
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1995.64062667.x
Subject(s) - protein kinase c , staurosporine , exocytosis , chromaffin cell , enzyme , secretion , chemistry , endocrinology , medicine , protein kinase a , agonist , biophysics , biology , microbiology and biotechnology , biochemistry , catecholamine , adrenal medulla , receptor
We investigated the interaction between Pb 2+ and protein kinase C (PKC) in the Pb 2+ ‐induced release of norepinephrine (NE) from permeabilized adrenal chromaffin cells. Our analysis of endogenous PKC activity in permeabilized cells suggests that Pb 2+ interacts with the adrenal enzyme at multiple sites. Pb 2+ activates the enzyme through high‐affinity ( K A(Pb) = 2.4 × 10 −12 M ) interactions and inhibits the enzyme by competitive and noncompetitive interactions with nanomolar‐( K i = 7.1 × 10 −9 M ) and micromolar‐ ( K ′ i = 2.8 × 10 −7 M ) affinity sites, respectively. Activation of PKC by 12‐ O ‐tetradecanoylphorbol 13‐acetate (TPA) in Ca 2+ ‐deficient, Pb 2+ ‐containing medium, enhances the Pb 2+ ‐induced NE release from permeabilized chromaffin cells by lowering the concentration of Pb 2+ required for half‐maximal activation of the secretory response from 7.5 × 10 −10 to 5.7 × 10 −11 M . The PKC inhibitors staurosporine and pseudosubstrate PKC (19–36) abolish the effect of TPA without affecting the Pb 2+ ‐induced secretion in the absence of TPA. These results indicate that (a) Pb 2+ is a partial agonist of PKC, capable of both activating and inhibiting the enzyme and (b) synergistic activation of PKC by TPA and Pb 2+ results in increased sensitivity of exocytosis to Pb 2+ but is not obligatory for Pb 2+ ‐triggered secretion.