抄録
Oxytocin (OT) secretion from magnocellular neurons of the supraoptic nucleus (SON) occurs from nerve terminals in the posterior pituitary and somata and dendrites in the SON and plays critical roles in parturition, lactation and synaptic plasticity in early post-natal life. Somato-dendritic OT secretion can be primed for activity-dependent release by thapsigargin (TG) which releases calcium from intracellular stores. Regulated secretion requires an increase in intracellular calcium concentration by calcium influx via voltage operated calcium channels (VOCCs). Using fluorescent immunohistochemistry, we found α-subunits for L-, P/Q-, N- and R-type VOCCs expressed in the somata and dendrites of OT neurons. Blocking N-type VOCCs was most effective, reducing high potassium stimulated (50mM) somato-dendritic secretion in vitro to 66±11% in adult female rats and 28±23% in post-natal day 8 rats (P<0.05, vs. control). TG-induced priming of high potassium stimulated OT release (447±90%, P<0.05 vs. control) was also reduced by blocking N-type VOCCs (to 133±18%, P<0.05). Whole-cell patch clamp recordings showed that calcium current carried by N-type VOCC was increased from 8±3 to 27±8 pA/pF (P<0.05) following TG treatment while currents carried by L, P/Q and R VOCCs were unaltered or decreased. These data suggest that high potassium-stimulated and primed somato-dendritic OT release involve an increase in calcium current carried predominately by N-type VOCCs. [J Physiol Sci. 2008;58 Suppl:S75]
