Ryanodine receptors neurons

The ryanodin receptor takes its name from its stimulation by the plant alkaloid ryanodin. In all, it has a similar composition to the InsPs receptor and is involved in Ca signal conduction in many excitatory cells (cells of banded and smooth musculature, neurons, etc.). 

In muscle cells and neurones a second mechanism exists for the release of intracellular Ca2-i-, involving ryanodine receptors in the endoplas mic reticulum (ER) membrane. This pathway is activated by an action potential opening a plasma membrane voltage-gated Ca2+ channel, allowing a small influx of extracellular Ca2+. Binding of Ca2+ to the ryanodine receptor triggers a massive release of Ca2+ from the ER stores. 

Hidalgo, C. (2005). Cross Talk Between Ca2+ and Redox Signalling Cascades in Muscle and Neurons Through the Combined Activation of Ryanodine Receptors/Ca2+ Release Channels. Philos Trans R Soc Land B Biol Sci 360(1464) 2237 16. 

Presynaptic NMDA receptors have also been reported to control GABA release. At intemeuron synapses onto Purkinje neurons, activation of NMDA receptors raised spontaneous GABA release, and this effect lasted for more than 10 minutes voltage-gated Ca2+ channels were not involved, but a blockade of ryanodine receptors attenuated the enhancement of GABA release and restricted the effect by time... 

We found that a GSH deficit reversed the direction of DA modulation of NMDA responses (Steullet et al., 2008). In control neurons, DA enhanced NMDA responses. But in neurons with a BSO-induced GSH deficit, DA decreased NMDA responses via activation of D2-type receptors. This decrease disappeared when normal GSH levels were restored by GSH-ethyl ester, a membrane-permeable GSH analog. The difference in dopamine modulation of NMDA responses in control neurons and in neurons with a GSH deficit was mostly explained by a differential modulation of L-type calcium channels. DA enhanced the function of these channels in control neurons, but decreased it in BSO-treated neurons. The redox-sensitive ryanodine receptors (RyRs), which were enhanced in BSO-treated neurons, played an essential role in altering DA signaling in neurons with a GSH deficit. These data suggest that enhancement of the function of RyRs in neurons with low GSH levels favors D2-type receptor-mediated and calcium-dependent pathways, causing a change in DA modulation of L-type calcium channels and ultimately in DA modulation of NMDA responses. 

Steullet P, Lavoie S, Kraftsik R, Guidi R, Gysin R, et al. 2008. A glutathione deficit alters dopamine modulation of L-type calcium channels via D2 and ryanodine receptors in neurons. Free Radical Biol Med 44 1042-1054. 

In skeletal muscle open voltage-gated L-type Ca2+ channels can interact directly with muscle ER (sarcoplasmic reticulum) ryanodine receptors to open the ryanodine receptor Ca2+ channel and thence elevate cytosolic Ca2+ concentration from sarcoplamic. reticulum Ca2+ stores. However in neurons and cardiac muscle activation of PM voltage-gated Ca2+ channels indirectly activates ryanodine receptor Ca2+ channels as outlined in the section on Ligand-gated Ca2+ channels . 

Pessah IN. 1997. Non-coplanar PCBs alter neuronal Ca regulation and neuroplasticity by a FKBP12/ryanodine receptor-mediated mechanism. Toxicologist 36 333. 

At the neuromuscular junction, ACh activates the nicotinic AChR, resulting in a Na+ influx and a depolarisation. This event generates an action potential which spreads along the membrane via voltage-gated Na+ channels (discussed in above) Muscle cells and neurons possess Ca2+ channels [57], the so-called ryanodine reptors (regulated by the alkaloid ryanodine Table 10), and IP3-sensitive Ca2+ channels. In skeletal muscle cells, ryanodine receptors are located in the sarcoplasmic reticulum (SR)... 

This hypothesis was further supported using molecular biology and cellular tools where the insect ryanodine receptor gene was heterologously expressed in appropriate cells. In untransfected CHO cells, application of flubendiamide sulfoxide (a better soluble analogue) did not cause an [Ca ] increase (Figure 8). In CHO cells transfected with the RyR from Drosophila (CHO-RyR), flubendiamide sulfoxide induced Ca responses with similar kinetic responses to those found in Heliothis neurons (Figure 8). 

Figure 8. Fiubendiamide activated the Drosophila RyR expressed in CHO ceiis. Un-transfected control CHO cells did not respond to caffeine or fiubendiamide sulfoxide with an increase of [Ca, in contrast to CHO cells which were transfected with a full-length cDNA of the Drosophila ryanodine receptor. Both compounds induced Ca responses with similar kinetics as to those found in Heliothis neurons.

To assess activity at the insect ryanodine receptor, pyridyl pyrazoles of Table II were tested in a calcium mobilization assay, using neurons from the American cockroach, Periplaneta americana. These studies have confirmed the mode of action to be RyR activation. Compounds D11-D17 showed exceptional potency in this assay with activity in the range of0.03-0.30 pM. The data shows the ability of anthranilic diamides to release internal calcium stores while failing to activate voltage-gated calcium channels. Furthermore, calcium mobilization induced by anthranilic diamides is blocked following treatment with 1 pM ryanodine, consistent with action at the ryanodine receptor. 

The anthranilamide, DP-012, stimulates a rise in [Ce ]i under conditions of Ca -free saline similar to that observed with standard saline, indicating that this chemistry mobilizes calcium from internal calcium stores rather than through external entry via voltage-gated Ca channels. Three possible targets are involved in release of internal calcium stores, inositol trisphosphate receptors (IP3RS), ryanodine receptors (RyRs), and sarco-endoplasmic reticulum ATPase (SERCA). These P. americana neurons possess fimctional ryanodine receptors. 

The current study shows that phthalic acid diamide insecticides, represented by flubendiamide and its sulfoxide analogue, activated ryanodine receptors present in isolated Heliothis neurons, as concluded from the following results. Firstly, calcium transients evoked by phthalic acid diamides were independent of the extracellular [Ca ], in contrast to the signals elicited by acetylcholine. This was interpreted as calcium release from intracellular stores of the endo(sarco)plasmic reticulum, which could in principle be mediated by two different release channels, namely the ryanodine receptor and the IP3 receptor. 

It is generally accepted that [ H]iyanodine binds with low nanomolar affinity to a calcium-conducting conformational state of the RyR channel. Consequently, [ H]ryanodine binding is frequently used to assess the function of ryanodine receptors (6 21). So in the context of this discussion, potentiation or attenuation of ryanodine affinity are consistently interpreted as channel activation or inactivation, respectively. The validity of this assumption has been confirmed by correlating [ HJryanodine binding results with direct calcium release measurements in isolated Heliothis neurons. 

Chavis P, Fagni L, Lansman JB, Bockaert J. Functional coupling between ryanodine receptors and L-type calcium chaimels in neurons. Nature. 1996 382(6593) 719-722. 

Solovyova N., and Verkhratsky A. 2003 Neuronal endoplasmic reticulum acts as a single functional Ca2+ store shared by ryanodine and inositol-1,4,5-trisphosphate receptors as revealed by intra-ER [Ca2+] recordings in single rat sensory neurones. Pflugers Arch 446, 447—454. 

Walton PD, Airey JA, Sutko JL, Beck CF, Mignery GA, Sildhof TC, Deerink T, Ellisman M (1991) Ryanodine and inositol triphosphate receptors coexist in avian cerebellar Purkinje neurons. J Cell Biol //i l 145-1157. 

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