Proceedings of The Physiological Society
King's College London (2011) Proc Physiol Soc 22, C05
NO signalling potentiates neuronal CaV2.1 and CaV2.2 in the mouse Medial Nucleus of the Trapezoid Body (MNTB) by different mechanisms.
A. Tozer1, I. D. Forsythe1, J. R. Steinert1
1. MRC Toxicology Unit, University of Leicester, Leicester, United Kingdom.
Nitric Oxide (NO) is a diffusible second messenger that modulates ion channels and contributes to synaptic plasticity. In light of its known modulation of high voltage-activated (HVA) potassium channels in the postsynaptic principal neurons of the medial nucleus of the trapezoid body (MNTB) (Steinert et al., 2008), we have investigated its modulation of native voltage-gated calcium channels (CaV). Using barium as the charge carrier, whole-cell patch recordings were made from in vitro brain slices from P13-15 CBA mice. Slices were incubated with nNOS inhibitor 7-nitroindazole (7-NI, 10µM) and treated with pharmacological channel blockers to isolate identified Ca2+ currents. Unpaired observations in the presence and absence of the NO donor sodium nitroprusside (SNP, 100µM) were made to elucidate NO-dependent modulation of the expressed CaV subtypes. Results showed that there was a differential effect of NO on the channel subtypes: the CaV1 (L-type) conductance was unaffected by NO, whereas CaV2.1 and CaV2.2 (P/Q and N-type) conductances were potentiated. P-type current was increased from 0.53±0.04nA (n=9, mean±SEM) to 0.82±0.04nA (n=6, mean±SEM) and N-type from 0.24±0.02nA (n=4, mean±SEM) to 0.42±0.07nA (n=9, mean±SEM). Our results also showed that CaV2.1 channels were potentiated via the canonical NO-cGMP pathway, as SNP induced potentiation was abolished in the presence of the guanylyl cyclase blocker 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1µM). In contrast, NO-dependent potentiation of N-type channels was not removed by inhibition of guanylyl cyclase activity, and this suggests that this channel subtype is modulated via a different pathway, i.e. by nitrosylation. This shows for the first time that NO-dependent modulation of a host of differentially expressed postsynaptic CaV channels can occur and our findings provide insights in to the mechanisms of cGMP-dependent and -independent regulation of voltage-gated Ca2+ entry by NO.
Where applicable, experiments conform with Society ethical requirements