Does calmodulin mediate stimulus-secretion coupling in the parotid gland? Studies using trifluoperazine

Area of Science:

• Biochemistry
• Cell Biology
• Pharmacology

Background:

• Calmodulin (CaM) is a key calcium-binding protein involved in cellular signaling.
• Cyclic AMP phosphodiesterase (PDE) regulates intracellular cyclic AMP levels.
• Rat parotid glands are a model system for studying exocrine secretion.

Purpose of the Study:

• To investigate the role of calmodulin in regulating cyclic AMP phosphodiesterase activity in rat parotid homogenates.
• To determine the effect of trifluoperazine, a calmodulin inhibitor, on parotid gland secretion stimulated by various agonists.

Main Methods:

• Assay of cyclic AMP phosphodiesterase activity in rat parotid homogenates.
• Measurement of amylase and potassium (K+) release from rat parotid slices.
• Assessment of cellular adenosine triphosphate (ATP) content.
• Incubation of parotid slices with varying concentrations of trifluoperazine.

Main Results:

• Calmodulin activated cyclic AMP phosphodiesterase by 8-10 fold in a calcium-dependent manner.
• Trifluoperazine inhibited calmodulin-activated phosphodiesterase with a half-maximal inhibitory concentration of 12 microM.
• Low concentrations of trifluoperazine (up to 40 microM) did not affect basal amylase/K+ release, ATP content, or isoproterenol/substance P-stimulated responses.
• Trifluoperazine (20-40 microM) inhibited amylase secretion induced by isoproterenol, dibutyryl cyclic AMP, carbamoylcholine, and phenylephrine.

Conclusions:

• Calmodulin plays a role in regulating cyclic AMP phosphodiesterase activity in rat parotid glands.
• Calmodulin inhibition by trifluoperazine selectively blocks amylase secretion induced by diverse agonists, suggesting its involvement in the secretory pathway downstream of initial receptor activation.
• These findings highlight the potential involvement of calmodulin in modulating exocrine secretion in the parotid gland.