The Inositol Phosphate-Calcium Signalling System in Lacrimal Gland Cells

Abstract

In lacrimal gland cells, receptor-activated Ca²⁺ mobilization involves two phases: 1) Ca²⁺ release from an intracellular store, and 2) a more prolonged phase of extracellular Ca²⁺ entry (Parod and Putney, 1978; Putney, 1987). These two phases of the Ca²⁺ response can be dissected by stimulating cells with a phospholipase C-linked agonist in the presence or absence of extracellular Ca²⁺. In the absence of extracellular Ca²⁺, such stimulation results in a transient increase in Ca²⁺, originating from the release of a finite intracellular Ca²⁺ pool. In the presence of physiological (mM) extracellular Ca²⁺, the elevation in [Ca²⁺]_i is sustained due to the additional component of extracellular Ca²⁺ influx. Extracellular Ca²⁺ influx is also the source for refilling of the intracellular Ca²⁺ pool upon termination of receptor activation.