Neuronal nitric oxide synthase modulates basal catecholamine secretion in bovine chromaffin cells

Abstract

The role of endogenously produced nitric oxide (NO) in the regulation of basal catecholamine (CA) secretion was studied in chromaffin cells. Treatment of chromaffin cells with nitric oxide synthase (NOS) inhibitors produced a dose-dependent increase in basal catecholamine secretion, which paralleled their ability to inhibit NOS activity. This inhibitory profile was similar to that found in neurons, suggesting the constitutive expression of neuronal NOS (nNOS) in these cells, which was confirmed by Western blot analysis. A study of the kinetics and pharmacology of nNOS activity expressed in chromaffin cells in culture indicated that NOS activity is calcium-dependent, increases with time, and is highly dependent on both intracellular concentrations of L-arginine (K(m) approximately 4 microM, V(max) = 908 +/- 60 pmol/hr x 10(6) cells) and transport of L-arginine into the cells (exhibiting two affinity constants of k(1) = 3.2 +/- 0.3 microM and k(2) = 126 +/- 5.5 microM). The effects of NOS inhibitors on CA secretion were mediated by the L-arginine-NO-cGMP pathway, insofar as exogenous L-arginine was able to partially block the increase in CA secretion evoked by them, and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ), a specific inhibitor of guanylate cyclase, and zaprinast, an inhibitor of the cGMP phosphodiesterase, were able to increase and inhibit, respectively, basal CA secretion in a dose-dependent manner. These results suggest that chromaffin cells exhibit a tonic production of NO by nNOS that keeps the basal CA secretion at low levels, and this could be necessary for maintaining a normotensive state.

Nitric oxide and the control of catecholamine secretion in rainbow trout Oncorhynchus mykiss

“…In mammals, studies suggest that NO inhibits catecholamine secretion by promoting a cascade of events beginning with activation of sGC and leading to phosphorylation of Ca 2+ channels and an attenuation of the inward Ca 2+ flux in response to stimulation (Schwarz et al, 1998;Ferrero et al, 2000;Hirooka et al, 2000;Vicente et al, 2002). In the present study, the sGC inhibitor, ODQ, was used to prevent Ca 2+ channel phosphorylation during electrical stimulation.…”

“…On the basis of previous studies on mammals, nNOS is believed to be the main isoform regulating of catecholamine secretion (Schwarz et al, 1998;Vicente et al, 2002). However, there is also evidence implicating eNOS (Torres et al, 1994;Barnes et al, 2001).…”

“…In rainbow trout Oncorhynchus mykiss, nNOS was localized in the head kidney tissue (Jimenez et al, 2001) but, unlike in mammals, it appears to be only sparsely present in chromaffin cells (Gallo and Civinini, 2001). Several studies have implicated nNOS in catecholamine regulation in mammals (Schwarz et al, 1998;Vicente et al, 2002;Barnes et al, 2001) whereas fewer studies have implicated endothelial NOS (eNOS) (Barnes et al, 2001;Torres et al, 1994); there is no evidence for a role for inducible NOS (iNOS).…”

“…Results from these studies were obtained using cultured chromaffin cells (Torres et al, 1994;Oset-Gasque et al, 1994;RodriguezPascual et al, 1995;Vicente et al, 2002) or perfused adrenal glands (Marley et al, 1995;Nagayama et al, 1998;Barnes et al, 2001). These prior studies have relied mainly on pharmacological approaches including the use of NO itself (Oset-Gasque et al, 1994), NO donors, SNP and/or SNAP (Marley et al, 1995;Schwarz et al, 1998) and/or NOS inhibitors (Torres et al, 1994;Nagayama et al, 1998;Schwarz et al, 1998;Barnes et al, 2001;Vicente et al, 2002).…”

Hydrogen sulfide stimulates catecholamine secretion in rainbow trout (Oncorhynchus mykiss)

“…The stimulatory effect of H 2 S on catecholamine secretion is in marked contrast to the effects of another endogenously produced gaseous neurotransmitter, NO, which acts to inhibit catecholamine secretion during chromaffin cell stimulation (19,20,42). Interestingly, unlike the situation for H 2 S, the secretion of NO during electrical stimulation of the perfused PCV preparation is dependent on pulse frequency (19).…”