Effect of caffeine on the secretion of peroxidase in rat submandibular gland: a study of its mechanism of action

Relationship between nitric oxide- and calcium-dependent signal transduction pathways in growth hormone release from dispersed goldfish pituitary cells

Nitric oxide (NO) and Ca(2+) are two of the many intracellular signal transduction pathways mediating the control of growth hormone (GH) secretion from somatotropes by neuroendocrine factors. We have previously shown that the NO donor sodium nitroprusside (SNP) elicits Ca(2+) signals in identified goldfish somatotropes. In this study, we examined the relationships between NO- and Ca(2+)-dependent signal transduction mechanisms in GH secretion from primary cultures of dispersed goldfish pituitary cells. Morphologically identified goldfish somatotropes stained positively for an NO-sensitive dye indicating they may be a source of NO production. In 2h static incubation experiments, GH release responses to the NO donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) were attenuated by CoCl2, nifedipine, verapamil, TMB-8, BHQ, and KN62. In column perifusion experiments, the ability of SNP to induce GH release was impaired in the presence of TMB-8, BHQ, caffeine, and thapsigargin, but not ryanodine. Caffeine-elicited GH secretion was not affected by the NO scavenger PTIO. These results suggest that NO-stimulated GH release is dependent on extracellular Ca(2+) availability and voltage-sensitive Ca(2+) channels, as well as intracellular Ca(2+) store(s) that possess BHQ- and/or thapsigargin-inhibited sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPases, as well as TMB-8- and/or caffeine-sensitive, but not ryanodine-sensitive, Ca(2+)-release channels. Calmodulin kinase-II also likely participates in NO-elicited GH secretion but caffeine-induced GH release is not upstream of NO production. These findings provide insights into how NO actions many integrate with Ca(2+)-dependent signalling mechanisms in goldfish somatotropes and how such interactions may participate in the GH-releasing actions of regulators that utilize both NO- and Ca(2+)-dependent transduction pathways.

Caffeine increases the expression of cystatin SN in human submandibular acinar-like HSG cells

OBJECTIVE

The study aimed at evaluating in vitro the effect of caffeine on expression of cystatin SN, a potential marker of sensitivity to bitterness in humans.

METHODS

Differentiation of human submandibular gland (HSG) cells was induced by culturing cells on Matrigel. Caffeine cytotoxicity was assessed over 3 days by the Resazurin test. Finally, effects of 5, 50 and 100μM caffeine exposure on cystatin SN expression were explored over 3 days by ELISA.

RESULTS

At concentrations relevant to human adult plasma levels (5, 50 and 100μM), caffeine did not affect cell viability whether cells were differentiated or not. Cystatin SN levels were overall higher in differentiated cells and increased with time in both conditions. There was a significant (p<0.001) effect of caffeine on cystatin SN expression specifically in differentiated cells.

CONCLUSIONS

The HSG cell line proved to be a relevant tool to study in vitro the effect of caffeine at concentrations consistent with dietary intake in human subjects. The results suggest that salivary cystatin SN abundance may depend on caffeine intake, with possible consequences on taste sensitivity.