Nitric oxide augments single persistent Na⁺channel currents via the cGMP/PKG signaling pathway in Kenyon cells isolated from cricket mushroom bodies

Abstract

The nitric oxide (NO)/cyclic GMP signaling pathway has been suggested to be important in the formation of olfactory memory in insects. However, the molecular targets of the NO signaling cascade in the central neurons associated with olfactory learning and memory have not been fully analyzed. In this study, we investigated the effects of NO donors on single voltage-dependent Na+ channels in intrinsic neurons, called Kenyon cells, in the mushroom bodies in the brain of the cricket. Step depolarization on cell-attached patch membranes induces single-channel currents with fast-activating and -inactivating brief openings at the beginning of the voltage steps followed by more persistently recurring brief openings all along the 150-ms pulses. Application of the NO donor S-nitrosoglutathione (GSNO) increased the number of channel openings of both types of single Na+ channels. This excitatory effect of GSNO on the activity of these Na+ channels was diminished by KT5823, an inhibitor of protein kinase G (PKG), indicating an involvement of PKG in the downstream pathway of NO. Application of KT5823 alone decreased the activity of the persistent Na+ channels without significant effects on the fast-inactivating Na+ channels. The membrane-permeable cGMP analog 8Br-cGMP increased the number of channel openings of both types of single Na+ channels, similar to the action of NO. Taken together, these results indicate that NO acts as a critical modulator of both fast-inactivating and persistent Na+ channels and that persistent Na+ channels are constantly upregulated by the endogenous cGMP/PKG signaling cascade. NEW & NOTEWORTHY This study clarified that nitric oxide (NO) increases the activity of both fast-inactivating and persistent Na+ channels via the cGMP/PKG signaling cascade in cricket Kenyon cells. The persistent Na+ channels are also found to be upregulated constantly by endogenous cGMP/PKG signaling. On the basis of the present results and the results of previous studies, we propose a hypothetical model explaining NO production and NO-dependent memory formation in cricket large Kenyon cells.

Nitric oxide down-regulates voltage-gated Na+ channel in cardiomyocytes possibly through S-nitrosylation-mediated signaling

“…Although our study could not detect the acute effects of NO donor on I Na , previous several studies identified NO/cGMP/PKG pathway to regulate I Na as a short-term effect 16 , 27 , 35 . Because the life span of NO in blood milieu or in the bathing solution is less than 0.2 ms 30 , biological exposure time of NO largely depends on the NO-releasing speed of NO donor.…”

Nitric oxide down-regulates voltage-gated Na+ channel in cardiomyocytes via transcriptional S-nitrosylation signaling pathway

“…Although our study could not detect the acute effects of NO donor on I Na , previous several studies identi ed NO/cGMP/PKG pathway to regulate I Na as a short-term effect [16,27,35]. Because the life span of NO in blood milieu or in the bathing solution is less than 0.2 ms [30], biological exposure time of NO largely depends on the NO-releasing speed of NO donor.…”

Nitrergic modulation of ion channel function in regulating neuronal excitability

“…In parallel, in cultured hippocampal rat CA1 neurons, a NO donor (SNAP, 100 µM) activated Na P [ 50 ] suggesting a species independent and conserved mechanism. Further evidence for NO’s effects on Na P is provided by a study in Kenyon cells isolated from cricket mushroom bodies in which the NO donor GSNO (10 µM) enhances the number of single channel openings in a cGMP and PKG-dependent manner, highlighting that NO acts as a modulator of both fast-inactivating and persistent sodium channels and that persistent sodium channels are constantly upregulated by the endogenous cGMP/PKG signaling cascade [ 51 ]. In contrast, in DRG neurons, NO suppresses Na P currents in a cGMP-independent manner [ 49 ], further adding to the complex and diverse functions of NO signaling.…”