Protein Kinase C Isoforms Differentially Control Lacrimal Gland Functions

Abstract

Lacrimal gland protein secretion is primarily under the control of cholinergic muscarinic and αl-adrenergic receptors.¹ Cholinergic agonists are coupled to the activation of phospholipase C (PLC),² which leads to the production of two second messenger molecules: inositol 1,4,5-trisphosphate (IP₃) and diacylglycerol (DAG). IP₃ increases the cytoplasmic concentration of calcium ([Ca²⁺]_i) and DAG activates protein kinase C (PKC), two events that are thought to trigger protein secretion.¹ Lacrimal gland α_l-adrenergic receptors are of particular interest. Unlike those in other tissues, they are not coupled to the PLC pathway, although their activation leads to a slight increase in [Ca²⁺]_i.³ We have also shown that these receptors are not linked to the activation of phospholipase D in lacrimal gland acini.⁴ Thus the transduction pathway(s) used by the α₁-adrenergic receptors to trigger lacrimal gland protein secretion remains to be identified.