Ghrelin Selectively Inhibits Ca_V3.3 Subtype of Low-Voltage-Gated Calcium Channels

The mechanisms by which ghrelin controls electrical activity in the hypothalamus are not fully understood. One unexplored target of ghrelin is Ca_V3, responsible for transient calcium currents (T-currents) that control neuronal firing. We investigated the effect of ghrelin on Ca_V3 subtypes and how this modulation impacts on neuronal activity. We performed whole-cell patch-clamp recordings in primary mouse hypothalamic cultures to explore the effect of ghrelin on T-currents. We also recorded calcium currents from transiently transfected tsA201 cells to study the sensitivity of each Ca_V3 subtype to GHSR activation. Finally, we ran a computational model combining the well-known reduction of potassium current by ghrelin with the Ca_V3 biophysical parameter modifications induced by ghrelin to predict the impact on neuronal electrical behavior. We found that ghrelin inhibits native NiCl₂ sensitive current currents in hypothalamic neurons. We determined that Ca_V3.3 is the only Ca_V3 subtype sensitive to ghrelin. The modulation of Ca_V3.3 by ghrelin comprises a reduction in maximum conductance, a shift to hyperpolarized voltages of the I-V and steady-state inactivation curves, and an acceleration of activation and inactivation kinetics. Our model-based prediction indicates that the inhibition of Ca_V3.3 would attenuate the stimulation of firing originating from the inhibition of potassium currents by ghrelin. In summary, we discovered a new target of ghrelin in neurons: the Ca_V3.3. This mechanism would imply a negative feed-forward regulation of the neuronal activation exerted by ghrelin. Our work expands the knowledge of the wide range of actions of GHSR, a receptor potentially targeted by therapeutics for several diseases.