Activated Protein Kinase Activity in Contractile Smooth Muscle

MAPK is more likely to be the physiologically relevant caldesmon kinase since there is no evidence to date for p34 i 2 or any PDPK other than MAPK, in arterial muscle (Adam and Hathaway, 1993 Adamef a/., 1995). With the use of a specific peptide substrate, the 42- and 44-kDa isoforms of MAPK (p42mapk and p44MAPK) were found to contain all the proline-directed protein kinase activity in contractile smooth muscle. However, it is possible that PDPKs other than MAPK exist in smooth muscle and that (1) the activity of these are not detected using this peptide substrate and (2) they phosphorylate caldesmon. 

Several Elements of the Mitogen-Activated Protein Kinase Cascade Are Present in 

In addition to these elements of the MAPK cascade, contractile smooth muscle contains hetero-trimeric GTP binding proteins that may activate MAPK. Adrenergic stimulation of contractile smooth muscle has pronounced effects on contractility that are not explained by a simple alteration in intracellular free calcium (Aburto et al., 1993). Furthermore, it is known that adrenergic stimulation can cause a G -dependent increase in MAPK activity in some tissues. It is possible that some of the actions of adrenergic agonists on smooth muscle contractile behavior involve the activation of MAPK, since elements of the pathway linking adrenergic stimulation to MAPK are present in contractile smooth muscle. 

MAPK is active when isolated from chicken gizzard, rat aorta, and porcine carotid smooth muscles 

FIGU R E 2 Line graph (A) and immunoblots (B,C) showing separation of MAPK isoforms by Mono-Q fast-performance liquid chromatography (Adam et al., 1995). Extracts of porcine carotid arteries were separated on a 1-ml Mono-Q column. Aliquots from each fraction were assayed for MAPK activity (A). Only fractions containing activity above background are presented for clarity. Proteins from specified fractions were separated by SDS-polyacrylamide gel electrophoresis, transferred to nitrocellulose, and assayed by immu-noblot for the presence of either MAPK (B) or phosphotyrosine (C). Reprinted with permission. Circulation Research. Copyright 1995 American Heart Association. 

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