IMBICE   05372
INSTITUTO MULTIDISCIPLINARIO DE BIOLOGIA CELULAR
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Modulation of neuronal voltage-operated calcium channels by melanocortin receptor type 4 (MC4R)
Autor/es:
FRANCINA AGOSTI; EDUARDO JAVIER LÓPEZ SOTO; SILVIA RODRÍGUEZ; MARIO PERELLO; JESICA RAINGO
Lugar:
Buenos Aires
Reunión:
Congreso; 5th Special Conference of the International Society for Neurochemistry-?Synapses and dendritic spines in health and disease?; 2012
Resumen:
Melanocortin receptor type 4 (MC4R) is a G protein coupled receptor highly expressed in neurons involved in appetite control. MC4R mutations are, by far, the most common cause of monogenic obesity in humans. MC4R binds to a-MSH and its activation impacts on many aspects of neuronal function, including synaptic activity. Moreover, MC4R exhibits basal activity. Presynaptic neuronal voltage operated calcium channels (VOCC) control neurosecretion. Two different genes encode pre-synaptic VOCC: CaV2.1 and CaV2.2. These channels are highly sensitive to G protein coupled receptor-mediated modulation. Here we investigated how MC4R basal and evoked activity impact on CaV2.1 and CaV2.2 function. We used the patch clamp technique in transfected HEK293 cells co-expressing CaV2.1 or CaV2.2, the auxiliary subunits of calcium channels and an MC4R-containing plasmid with the soluble GFP sequence. We found that MC4R co-expression specifically reduced CaV2.1 basal calcium currents (% of GFP positive cells with current: CaV2.1 and MC4R = 28%, CaV2.1 only = 70%) while it did not alter CaV2.2 basal current levels (% ofGFP positive cells with current: CaV2.2 and MC4-R = 95%, CaV2.2 only = 95%), suggesting a differential effect of MC4R basal activity on CaV2.1 function. When we applied the MCR agonist melanotan-II (MTII) to HEK293 cells co-expressing CaV2.2 and MC4R, we found a concentration dependent inhibitory effect on CaV2.2 currents (EC50~80 nM). When we evaluated MTII effect on three cells co-expressing CaV2.1 and MC4R that displayed calcium currents (ranging 60?100 pA) we found no effect of MTII at saturating dose (250 nM). Our results suggest that MC4R activity would have a differential effect on the two major presynaptic calcium channels: CaV2.1 is inhibited by basal MC4R activity and CaV2.2 is sensitive to agonist-evoked MC4R activity. We are now investigating these two separate pathways in terms of the G protein and second messenger involved. Supported by CONICET (EJLS, MP and JR), CIC-PBA (FA and SR), PICT2010?1589 (JR) and PICT2010?1954 (MP).