Nitric Oxide Signalling Augments Neuronal Voltage-Gated L-Type (CaV1) and P/Q-Type (CaV2.1) Channels in the Mouse Medial Nucleus of the Trapezoid Body

PLOS ONE, February 2012

22389692

Adam J. B. Tozer, Ian D. Forsythe, Joern R. Steinert

Nitric Oxide (NO) is a diffusible second messenger that modulates ion channels, intrinsic excitability and mediates synaptic plasticity. In light of its activity-dependent generation in the principal neurons of the medial nucleus of the trapezoid body (MNTB), we have investigated its potential modulatory effects on native voltage-gated calcium channels (Ca(V)) within this nucleus. Whole-cell patch recordings were made from brain slices from P13-15 CBA mice. Slices were incubated with the inhibitor of neuronal nitric oxide synthase (nNOS) 7-nitroindazole (10 µM) and pharmacological blockers used to isolate Ca(2+) current subtypes. Unpaired observations in the presence and absence of the NO-donors sodium nitroprusside (SNP, 100 µM) or Diethyl-ammonium-nonoate (DEA, 100 µM) were made to elucidate NO-dependent modulation of the expressed Ca(V) subtypes. A differential effect of NO on the calcium channel subtypes was observed: Ca(V)1 and Ca(V)2.1 (L+R- and P/Q+R-type) conductances were potentiated, whereas N+R-type (Ca(V)2.2) and R-type (Ca(V)2.3) current amplitudes were unaffected. L+R-type currents increased from 0.36 ± 0.04 nA to 0.64 ± 0.11 nA and P/Q+R-type from 0.55 ± 0.09 nA to 0.94 ± 0.05 nA, thereby changing the balance and relative contribution of each subtype to the whole cell calcium current. In addition, N+R-type half-activation voltage was left shifted following NO exposure. NO-dependent modulation of P/Q+R and N+R-type, but not L+R-type, channels was removed by inhibition of soluble guanylyl cyclase (sGC) activity. This data demonstrates a differential effect of NO signalling on voltage-gated calcium entry, by distinct NO-dependent pathways.