title: Essential role of myosin light chain kinase in the mechanism for MgATP-dependent priming of exocytosis in adrenal chromaffin cells.
abstract: Ca(2+)-induced exocytosis in chromaffin cells now seems to consist of at least two distinct steps:MgATP-dependent Ca(2+)-dependent priming of the secretory apparatus, and Ca(2+)-dependent MgATP-independent step that triggers exocytosis (Bittner and Holz, 1992). Recently we found that a specific inhibitor of myosin light chain kinase (MLCK), wortmannin, inhibits Ca(2+)-induced catecholamine release from digitonin-permeabilized chromaffin cells, suggesting an implication of MLCK in the mechanisms of Ca(2+)-induced exocytosis (Imaizumi et al., 1992b). To elucidate further the implication of MLCK in the mechanism of exocytosis, we studied the effects of wortmannin and a peptide inhibitor (SM-1) corresponding to the pseudosubstrate domain of MLCK on MgATP-dependent and MgATP-independent release in digitonin-permeabilized chromaffin cells. Ca(2+)-induced exocytosis from the permeabilized cells in the presence of MgATP was inhibited by both SM-1 and wortmannin. Inhibitory effect of wortmannin on the rate of release induced by 10 microM Ca2+ in the presence of MgATP was much prominent in the later phase (1-10 min), although the initial rate was also decreased. SM-1 strongly inhibited ATP-dependent release without affecting Ca(2+)-dependent ATP-independent release at all. In addition, priming effect of MgATP that underlies Ca(2+)-dependent ATP-independent release was remarkably reduced by both wortmannin and SM-1. These results suggest that MLCK plays an essential role in ATP-dependent priming of Ca(2+)-induced exocytosis in chromaffin cells.
authors.affiliation: Life Science Institute, Sophia University, Tokyo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kumakura
authors.forename: K
authors.initials: K
authors.lastname: Sasaki
authors.forename: T
authors.initials: T
authors.lastname: Sakurai
authors.forename: M
authors.initials: M
authors.lastname: Ohara-Imaizumi
authors.forename: H
authors.initials: H
authors.lastname: Misonou
authors.forename: S
authors.initials: S
authors.lastname: Nakamura
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuda
authors.forename: Y
authors.initials: Y
authors.lastname: Nonomura
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology / Q000502:physiology*; D000311:Adrenal Glands / Q000166:cytology / Q000502:physiology*; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000166:cytology / Q000502:physiology*; D005089:Exocytosis; D005455:Fluorescent Antibody Technique; D015151:Immunoblotting; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors / Q000494:pharmacology / Q000502:physiology*; D010446:Peptide Fragments / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D013997:Time Factors; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D002395:Catecholamines; C090955:K-MLC 11-23; D010446:Peptide Fragments; D010455:Peptides; C090954:SM 1 peptide; D000255:Adenosine Triphosphate; D009219:Myosin-Light-Chain Kinase; D002118:Calcium; D000077191:Wortmannin