Ghrelin selectively inhibits CaV3.3 subtype of low voltage activated Ca2+ channels

CORDISCO G. SANTIAGO; RODRIGUEZ SILVIA S.; MUSTAFÁ EMILIO ROMÁN,; RAINGO JESICA

San Diego

Congreso; 2018 meeting of the Society for Neuroscience; 2018

Society for Neuroscience

Voltage-gated Ca2+ (CaV) channels are instrumental in coupling changes in membrane voltage to Ca2+ influx that, in turn, regulates numerous critical neuronal functions. In particular, low voltage activated Ca2+ channels (CaV3) are involved in the generation of burst firing and pacemaker activity. Knowing that G-protein coupled receptors can modulate CaV3 activity, here we investigated the ghrelin effect on CaV3 currents through its receptor, GHSR. Previously, we have showed that ghrelin evoked GHSR activity inhibits high voltage activated CaV, particularly CaV2.1 and CaV2.2. Whole cell patch recordings on transfected tsA201 cells reveal that activation of GHSR by ghrelin application has an inhibitory effect on CaV3.3 currents but no effect either on CaV3.1 or CaV3.2. Application of ghrelin has no impact on CaV3.3 voltage dependency parameters (V1/2 and k of activation and Vrev). On the other hand, ghrelin accelerates the CaV3.3 activation and inactivation kinetics at hyperpolarized voltages (from -40 to -20 mV), while the kinetics of recovery from inactivation remains similar to control values. Based on this data, we hypothesized that ghrelin application could reduce the calcium entry by CaV3.3 channels in response to physiologically relevant stimuli, such as action potentials. In order to study the isolated efficacy of CaV3.3 to calcium entry during action potential train we measure Ca2+ currents using a hippocampal CA1 neuron firing recording as a voltage command in tsA201 cells expressing CaV3.3 and GHSR. We found that ghrelin reduces the calcium entry through CaV3.3 evoked by this stimulation paradigm. Similar to previous reports, CaV3.3 displayed current facilitation, and we found that this phenomenon is slightly reduced by ghrelin application. Next, we explore the signaling cascade implied in the effect of ghrelin on CaV3.3 and we found that co-expression of a Gq dominant negative mutant or co-expression of the regulator of G-protein signaling 2 (RGS2, an effector antagonist for Gq/11) completely occlude the inhibitory actions of ghrelin on CaV3.3. The data presented here allow us ascribing a ghrelin control of the firing activity in neurons expressing GHSR and CaV3.3, but further experiments are necessary to explore this possibility.