A novel role for carbon monoxide as a potent regulator of intracellular Ca²⁺ and nitric oxide in rat pancreatic acinar cells

Abstract

Carbon monoxide (CO) is known as an essential gaseous messenger that regulates a wide array of physiological and pathological processes, similar to nitric oxide (NO) and hydrogen sulfide. The aim of the present study was to elucidate the potential role of CO in Ca(2+) homeostasis and to explore the underlying mechanisms in pancreatic acinar cells. The exogenous application of a CO-releasing molecule dose-dependently increased intracellular Ca(2+) concentration ([Ca(2+)]i). A heme oxygenase (HO) inducer increased [Ca(2+)]i in a concentration-dependent manner, and the increase was diminished by an HO inhibitor. The CO-induced [Ca(2+)]i increase persisted in the absence of extracellular Ca(2+), indicating that Ca(2+) release is the initial source for the increase. The inhibition of G protein, phospholipase C (PLC), and inositol 1,4,5-trisphosphate (IP3) receptor diminished the CO-induced [Ca(2+)]i increase. CO upregulated endothelial nitric oxide synthase (eNOS) expression and stimulated NO production, and NOS inhibitor, calmodulin inhibitor, or the absence of extracellular Ca(2+) eliminated the latter response. Blocking the phosphatidylinositol 3-kinase (PI3K)-Akt/protein kinase B (PKB) pathway abolished CO-induced NO production. Pretreatment with an NOS inhibitor, NO scavenger, or soluble guanylate cyclase inhibitor, did not affect the CO-induced [Ca(2+)]i increase, indicating that NO, soluble guanylate cyclase, and cyclic guanosine 5'-monophosphate are not involved in the CO-induced [Ca(2+)]i increase. CO inhibited the secretory responses to CCK-octapeptide or carbachol. We conclude that CO acts as a regulator not only for [Ca(2+)]i homeostasis via a PLC-IP3-IP3 receptor cascade but also for NO production via the calmodulin and PI3K-Akt/PKB pathway, and both CO and NO interact. Moreover, CO may provide potential therapy to ameliorate acute pancreatitis by inhibiting amylase secretion.

Regulation of Intracellular Calcium by Carbon Monoxide in Human Bronchial Epithelial Cells

“…This effect appeared to be dependent on the CO released by CORM-2 because iCORM-2, which did not liberate CO, had no effect on the calcium levels. The time course is similar to what was previously observed in rat pancreatic acinar cells when 100 or 300 µM of CORM-2 was applied to the cells [31]. However, in pancreatic cells, the [Ca 2+ ] i changes were found to be oscillatory at medium concentrations (0.4 – 0.5 mM) in the extracellular solution, and monophasic (1 mM) at the highest concentration, which is typical of pancreatic acini cells when stimulated with physiological secretagogues such as CCK-8 or acetylcholine [31].…”

“…The time course is similar to what was previously observed in rat pancreatic acinar cells when 100 or 300 µM of CORM-2 was applied to the cells [31]. However, in pancreatic cells, the [Ca 2+ ] i changes were found to be oscillatory at medium concentrations (0.4 – 0.5 mM) in the extracellular solution, and monophasic (1 mM) at the highest concentration, which is typical of pancreatic acini cells when stimulated with physiological secretagogues such as CCK-8 or acetylcholine [31]. The fact that calcium increase induced by CORM-2 could be abolished in cells superfused with Ca 2+ -free KH solution or by pretreatment of the cells with PLC inhibitor U73122, suggests a joint participation of both intracellular calcium release and extracellular calcium entry.…”

“…The fact that calcium increase induced by CORM-2 could be abolished in cells superfused with Ca 2+ -free KH solution or by pretreatment of the cells with PLC inhibitor U73122, suggests a joint participation of both intracellular calcium release and extracellular calcium entry. This is different from pancreatic cells in which the increase in [Ca 2+ ] i was predominately due to PLC/IP 3 -triggered intracellular Ca 2+ mobilization [31]. CORM-2 could induce IP 1 accumulation in a concentration-dependent manner, and it is interesting to note that 10 µM CORM-2 almost induced the same amount of IP 1 production as that of 10 µM UTP, indicating that CO released by CORM-2 may be an effective PLC activator as compared to the activation of a G prote9 in-coupled receptor.…”

“…Therefore, it is possible that the activation of P2Y receptors could activate both SOCE and ROCE in human bronchial epithelia; thus, it would be interesting to test if CORM-2 has any effect on SOCE and/or ROCE. Although some reports suggest that CO maybe a regulator of ion channels [29], and that CO can inhibit T-type calcium channels in neuronal cells [30] and affect calcium signaling in pancreatic acinar cells [31], the regulatory effects of CO on intracellular calcium in human airway epithelia remain largely unknown. To our knowledge, this is the first study to examine the effect of CO released by CORM-2 on Ca 2+ signaling and its interaction with the purinergic signaling pathway in human bronchial epithelial cells.…”

How does cigarette smoking cause acute pancreatitis?

“…In fact, it has even been suggested that carbon monoxide may possess a potential therapeutic role in AP [97]. The various mechanisms suggested for its ameliorative effect in AP include regulation of intracellular Ca þ2 and NO e thereby controlling pancreatic exocrine secretion [98], suppression of nuclear factor NF-kappa B activation [99] as well as tissue protection and anti-proliferative effects [100].…”