Calcium Signalling in the Human Salivary Gland Cell Line

Background: A comprehensive understanding of stimulus-secretion coupling in human salivary glands is a prerequisite to understanding salivary gland pathology. The limited available comparative data suggest that an exclusive dependence on animal models may not be ideal. The Human Salivary Gland (HSG) cell line is an accessible and flexible alternative experimental model. However, characterisation of the signalling cascade in these cells is incomplete. Objective: To characterise stimulus-secretion coupling in HSG cells by direct comparison with that of mouse and human acinar cells. Methods: HSG cells were cultured on matrigel (Becton Dickinson, UK) coated glass coverslips using standard culture techniques and loaded with Fura-2 immediately before use. Agonist-evoked changes in intracellular calcium [Ca²⁺]_i were imaged microfluorimetrically (Cairn Research, UK). Results: Calcium mobilisation in HSG cells was stimulated by acetylcholine (ACh). The ACh concentration dependence in HSG and in mouse and human acinar cells included both oscillatory and steady-state components and a dependence on both intracellular stored Ca²⁺ and on Ca²⁺ influx. The responses of HSG cells to thapsigargin and ionomycin indicate that, like mouse and human acinar cells, almost all stored Ca²⁺ is concentrated within the endoplasmic reticulum by the sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase. HSG cells were quantitatively less sensitive to ACh than mouse or human acinar cells and Ca²⁺ signals in HSG cells showed a greater dependence on extracellular Ca²⁺. Preliminary data may also indicate differences in the kinetics of Ca²⁺ efflux in HSG cells. Conclusion: Overall, there appear to be many more similarities than differences in the Ca²⁺ signalling cascade in all cell types. In detail, some of the responses of HSG cell more closely mimic those of human acinar cells than do mouse acinar cells. Therefore, this study shows HSG cells to be a useful additional model for studying the mechanisms underlying human salivary gland physiology and pathophysiology.