A calmodulin dependent protein kinase in parietal cells

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Rabbit gastric parietal cells are crucial for acid secretion.
• Cytosolic protein kinases play vital roles in cellular signaling pathways.
• Calmodulin-dependent protein kinases (CaMKs) are involved in various cellular processes.

Purpose of the Study:

• To investigate the presence and characteristics of calmodulin-dependent protein kinase activity in isolated rabbit gastric parietal cells.
• To identify and characterize the substrates of this kinase.
• To determine the potential type of CaMK involved.

Main Methods:

• Isolation of rabbit gastric parietal cells.
• Assay of cytosolic protein kinase activity.
• Substrate identification using molecular weight and isoelectric focusing.
• Phosphorylation site analysis using tryptic peptide mapping.
• Enzyme inhibition studies with trifluoperazine.
• Comparation with kinase activity in rabbit pancreatic cytosol.

Main Results:

• An active cytosolic calmodulin-dependent protein kinase activity was identified in rabbit gastric parietal cells.
• A prominent 100 kDa substrate (pp100) was observed, phosphorylated on threonine residues.
• The kinase activity was inhibited by trifluoperazine (KI: 10-15 microM) and restored by exogenous calmodulin.
• Identical pp100 characteristics were found in rabbit pancreatic cytosol, phosphorylated by a calcium-dependent kinase.

Conclusions:

• A type III calmodulin-dependent kinase is likely present in the cytosol of rabbit gastric parietal cells.
• This kinase phosphorylates a specific 100 kDa protein substrate.
• The findings contribute to understanding the molecular mechanisms regulating parietal cell function.