Regulatory Aspects of Intracellular Magnesium in the Rat Parotid Gland

Methods: Rat parotid glands were digested by the use of colagenase and a cell suspension (CS) was obtained, then loaded with Magfura-2  for the measurement of [Mg²⁺]_i by established methods. [Mg²⁺]_i was determined in the presence of different extracellular Mg²⁺ concentrations ([Mg²⁺]₀) (0, 1.1, 5 & 10 mM). In another set of experiments [Mg²⁺]₀ was kept at 1.1 mM while cells were incubated in the presence membrane transport inhibitors and its effects on the [Mg²⁺]_i were observed at resting level and after stimulation with acetylcholine (ACh) 10^-5  M.  Results are expressed as mean +- SEM of fluorescence arbitrary units for [Mg²⁺]_i and were tested for mean differences with ANOVA plus post HOC tests. Values of P<0.05 were taken as significant.

Results:  In resting cells increasing  [Mg²⁺]₀ led to a significant increase in the [Mg²⁺]_i.  When incubated with membrane transport inhibitors resting cells showed a significant increase in [Mg²⁺]₀. Stimulation of the acinar cells with ACh resulted in significant decrease of [Mg²⁺]_i.

Mean (+- SEM) basal [Mg²⁺]_i in 1.1 mM [Mg²⁺]₀  and  in the presence of different transport inhibitors:

Conclusion: In rat parotid acinar cells  the existence of an anti-port Na⁺/Mg²⁺ implicated in the regulation of basal [Mg²⁺]_i  and the mobilisation of [Mg²⁺]_i in an anti-parallel way compared to intracellular calcium upon cellular stimulation with ACh is suggested.