Nitric oxide synthesis causes inositol phosphate production and Ca2+ release in rat parotid acinar cells

Abstract

The activity of nitric oxide synthase (NOS) in rat parotid acinar cells was measured using a newly synthesized fluorescent NO indicator DAF-2/DA. Our results show that NO production is most effectively stimulated by activation of the beta-adrenergic receptor, and to a minor extent by substance P (SP). NO activates the production of cGMP, an intracellular messenger that has been shown to release Ca2+ from ryanodine-sensitive intracellular stores. We found that cGMP is also able to release Ca2+ from ryanodine-insensitive intracellular stores. Our data show that a rise in the cGMP concentration induces inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] synthesis and Ca2+ release from intracellular stores.

Nitric oxide and cGMP activate Ca2+-release processes in rat parotid acinar cells

“…Although the results presented in this study allow the possibility of such a pathway, conclusive evidence is necessary to establish the link between the G kinase and ADP-ribosyl cyclase. The model also shows that cGMP synthesis leads to phospholipase C-mediated production of Ins(1,4,5)P $ [11], a process that is presumably mediated by a G kinase, as illustrated in Figure 9 by the dashed arrow. This pathway accounts for the Ca# + release that is not inhibited by ryanodine.…”

“…The relatively small rise in [cGMP] observed after stimulation of parotid acini with adrenaline, which activates both α-and β-adrenergic receptors, suggests that this kind of potentiation is not found in rat parotid acinar cells. It could easily be conceived that adrenaline activates synthesis of cGMP through receptor-mediated NO production [11]. However, with respect to substance P, a much smaller NO synthesis is observed [11] that might, in principle, be sufficient for activating the guanylate cyclase.…”

“…It could easily be conceived that adrenaline activates synthesis of cGMP through receptor-mediated NO production [11]. However, with respect to substance P, a much smaller NO synthesis is observed [11] that might, in principle, be sufficient for activating the guanylate cyclase. It is also a possibility that cGMP-mediated Ca 2 + release in parotid acinar cells substance P activates guanylate cyclase via a pathway that is not strongly dependent on NO synthesis.…”

“…NO, an activator of soluble guanylate cyclase, has previously been shown to cause an increase in the cellular [cGMP] in parotid acinar cells [11,12]. We found that stimulation of rat parotid acinar cells with 200 µM SNAP, a well-characterized NO donor that releases NO spontaneously within seconds of being dissolved [13], induces a strong sustained rise in the [cGMP] corresponding to an increase of 900 % after 10 s [11]. To investigate whether this rise in [cGMP] is associated with a change in [Ca# + ] i , we measured [Ca# + ] i in individual fura 2-loaded cells from rat parotid acini.…”

“…We found that the NO-induced Ca# + release in parotid acini was inhibited by about 40 % in the presence of ryanodine, consistent with a large part of the Ca# + release being mediated by a mechanism responsible for Ca# + -induced Ca# + -release processes. The incomplete inhibition in the presence of ryanodine is due to the activation by cGMP of Ins(1,4,5)P $ production, leading to Ca# + release from ryanodine-insensitive stores [11].…”