PT - JOURNAL ARTICLE AU - Michael Gray AU - Jorge Golowasch TI - Voltage-dependence of a neuromodulator-activated ionic current AID - 10.1523/ENEURO.0038-16.2016 DP - 2016 May 02 TA - eneuro PG - ENEURO.0038-16.2016 4099 - http://www.eneuro.org/content/early/2016/05/02/ENEURO.0038-16.2016.short 4100 - http://www.eneuro.org/content/early/2016/05/02/ENEURO.0038-16.2016.full AB - The neuromodulatory inward current (IMI) generated by crab Cancer borealis stomatogastric ganglion neurons, is an inward current whose voltage-dependence has been shown to be crucial in the activation of oscillatory activity of the pyloric network of this system. It has been previously shown that IMI loses its voltage-dependence in low extracellular calcium, but that this effect appears to be regulated by intracellular calmodulin. Voltage-dependence is only rarely regulated by intracellular signaling mechanisms. Here we address the hypothesis that the voltage-dependence of IMI is mediated by intracellular signaling pathways activated by extracellular calcium. We demonstrate that calmodulin inhibitors and a ryanodine antagonist can reduce IMI voltage-dependence in normal Ca++, but that, in low Ca++, calmodulin activators do not restore IMI voltage-dependence. Further, we show evidence that CaMKII alters IMI voltage-dependence. These results suggest that calmodulin is necessary but not sufficient for IMI voltage-dependence. We therefore hypothesize that the Ca++/calmodulin requirement for IMI voltage-dependence is due to an active sensing of extracellular calcium by a GPCR family calcium-sensing receptor (CaSR) and that the reduction in IMI voltage-dependence by a calmodulin inhibitor is due to CaSR endocytosis. Supporting this, pre-incubation with an endocytosis inhibitor prevented W7-induced loss of IMI voltage-dependence, and a CaSR antagonist reduced IMI voltage-dependence. Additionally, myosin light chain kinase, which is known to act downstream of CaSR, seems to play a role in regulating IMI voltage-dependence. Finally, a Gβγ-subunit inhibitor also affects IMI voltage-dependence, in support of the hypothesis that this process is regulated by a G-protein-coupled CaSR.Significance Statement: Neurons and neuronal networks display many forms of activity, of which oscillatory activity is crucial in many vital functions such as heartbeat, digestion and locomotion. What state a neuron exists in is often determined by its neuromodulatory environment. Recent studies have shown that many neuromodulators that enable oscillatory activity in neurons do so by activating voltage-gated inward currents that express a negative slope conductance. Such voltage-gating is normally an intrinsic property of the ion channels themselves, and are only rarely mediated by a separate signaling pathway or molecule. Here we characterize what we believe is a novel voltage-dependence mechanism that involves active extracellular calcium sensing by a dedicated receptor, and intracellular calcium-dependent processes that modulate voltage-dependence of this current.