Multiscale modelling of saliva secretion

- We review the construction of a multiscale model of saliva secretion.
- We predict that calcium oscillation frequency is unimportant for saliva secretion.
- We predict that Ca-sensitive K channels are situated in the apical membrane.
- We predict that saliva secretion is most efficient in the isoosmotic regime.
- Acinar spatial structure might be unimportant.

We review a multiscale model of saliva secretion, describing in brief how the model is constructed and what we have so far learned from it. The model begins at the level of inositol trisphosphate receptors (IPR), and proceeds through the cellular level (with a model of acinar cell calcium dynamics) to the multicellular level (with a model of the acinus), finally to a model of a saliva production unit that includes an acinus and associated duct. The model at the level of the entire salivary gland is not yet completed. Particular results from the model so far include (i) the importance of modal behaviour of IPR, (ii) the relative unimportance of Ca2+ oscillation frequency as a controller of saliva secretion, (iii) the need for the periodic Ca2+ waves to be as fast as possible in order to maximise water transport, (iv) the presence of functional K+ channels in the apical membrane increases saliva secretion, (v) the relative unimportance of acinar spatial structure for isotonic water transport, (vi) the prediction that duct cells are highly depolarised, (vii) the prediction that the secondary saliva takes at least 1 mm (from the acinus) to reach ionic equilibrium. We end with a brief discussion of future directions for the model, both in construction and in the study of scientific questions.