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Expression of Recombinant Calcium Channels Support Secretion in a Mouse Pheochromocytoma Cell Line

¹ Department of Neurobiology, Pharmacology, and Physiology, The University of Chicago, Chicago, Illinois 60637 ² Tufts University School of Medicine, New England Medical Center, Boston, Massachusetts 02111

Submitted 5 May 2003; accepted in final form 22 June 2003

We have characterized a recently established mouse pheochromocytoma cell line (MPC 9/3L) as a useful model for studying neurotransmitter release and neuroendocrine secretion. MPC 9/3L cells express many of the proteins involved in Ca²⁺-dependent neurotransmitter release but do not express functional endogenous Ca²⁺-influx pathways. When transfected with recombinant N-type Ca²⁺ channel subunits _1B,_2a,₂ (Ca_v2.2), the cells expressed robust Ca²⁺ currents that were blocked by -conotoxin GVIA. Activation of N-type Ca²⁺ currents caused rapid increases in membrane capacitance of the MPC 9/3L cells, indicating that the Ca²⁺ influx was linked to exocytosis of vesicles similar to that reported in chromaffin or PC12 cells. Synaptic protein interaction (synprint) sites, like those found on N-type Ca²⁺ channels, are thought to link voltage-dependent Ca²⁺ channels to SNARE proteins involved in synaptic transmission. Interestingly, MPC 9/3L cells transfected with either L_C-type (_1C, _2a, ₂, Ca_v1.2) or T-type (_1G, _2a, ₂, Ca_v3.1) Ca²⁺ channel subunits, which do not express synprint sites, expressed appropriate Ca²⁺ currents that supported rapid exocytosis. Thus MPC 9/3L cells provide a unique model for the study of exocytosis in cells expressing specific Ca²⁺ channels of defined subunit composition without complicating contributions from endogenous channels. This model may help to distinguish the roles that different Ca²⁺ channels play in Ca²⁺-dependent secretion.

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