Ageing and diabetes mellitus (DM) have previously been shown to elicit marked changes in parotid gland salivary function, in terms of its ability to secrete α-amylase, and in its morphological macrostructure. Both ageing and DM are associated with decreased α-amylase output and infiltration of numerous lipid vacuoles in the parotid gland compared with age-matched controls (Anderson, 1987). Since cytosolic calcium ([Ca²⁺]_i) plays a major role in the stimulus-secretion coupling process in most exocrine cells, then it is pertinent to investigate the homeostasis of this physiological divalent cation during ageing and DM compared with their respective controls. Diabetes mellitus was induced in adult male Wistar rats by a single intraperitoneal (I.P.) injection of streptozotocin (STZ, 60 mg (kg body wt)^-1; Sharma et al. 1985). Control animals were injected with a similar volume of citrate buffer. The animals were tested for DM 4 days after STZ injection and 2 months later when they were humanely killed for the experiment. Parotid glands from either age-matched control and diabetic rats or from two age groups of young (2Ð6 months) and aged (16 months) rats were isolated and subsequently dissociated into acinar cells using collagenase. Cells were loaded with 2 µM fura-2 AM for the measurement of [Ca²⁺]_i using fluorescence photometry (Pariente et al. 2000). All values are expressed as ratio units (F₃₄₀/F₃₈₀).

After 2 months of STZ treatment diabetic rats weighed significantly (Student’s unpaired t test; P < 0.001) less (mean ± S.E.M.; 232 ± 7.2 g, n = 8) compared with age-matched controls (381 ± 12.53 g, n = 8). Similarly, blood glucose level was much higher in diabetic rats (407.50 ± 35.90 mg dl^-1, n = 8) compared with control (81.20 ± 3.1 mg dl^-1, n = 8). Basal [Ca²⁺]_i in young (2Ð6 months) and aged (16 months) rats was 0.362 ± 0.008 (n = 11) and 0.411 ± 0.02 (n = 10), respectively. Stimulation of 16-month-old parotid acinar cells with acetylcholine (ACh; 1 X 10^-5 M) resulted in a significant (P < 0.05) decrease (in both the peak and plateau phases) in [Ca²⁺]_i compared with acinar cells obtained from 2- to 6-month-old rats. Peak values of 1.272 ± 0.05 (n = 11) and 1.022 ± 0.02 (n = 10) were recorded from parotid acinar cells isolated from 2- to 6- and 16-month-old animals, respectively. DM produced no significant change in basal [Ca²⁺]_i with values of 0.360 ± 0.008 (n = 17) compared with age-matched control values of 0.363 ± 0.008 (n = 11). Similarly, DM evoked no significant change in the initial peak [Ca²⁺]_i with values of 1.210 ± 0.03 (n = 17) compared with age-matched control values of 1.272 ± 0.05 (n = 11). In contrast, DM had a significant (P < 0.001) effect on the plateau phase of [Ca²⁺]_i measured 202.93 ± 0.29 s (n = 18) after ACh application. Typically, the [Ca²⁺]_i was 0.730 ± 0.01 (n = 18) and 0.958 ± 0.02 (n = 11) in DM and age-matched control fura-2 AM-loaded acinar cells, respectively. The results indicate that both DM and ageing are associated with decreased levels of [Ca²⁺]_i in parotid acinar cells in response to ACh stimulation. Ageing induces alteration in Ca²⁺ release from intracellular stores, whereas DM is associated with a decrease in Ca²⁺ entry into the cell.

All procedures accord with current UK legislation.