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Distinct omega‐agatoxin‐sensitive calcium currents in somata and axon terminals of rat supraoptic neurones.
Author(s) -
Fisher T E,
Bourque C W
Publication year - 1995
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1995.sp021059
Subject(s) - axon , voltage dependent calcium channel , calcium , neuroscience , chemistry , biophysics , patch clamp , electrophysiology , biology , organic chemistry
1. Voltage‐dependent calcium currents were measured at room temperature using whole‐cell patch clamp in acutely isolated somata and axon terminals of the magnocellular neurosecretory cells (MNCs) from the rat supraoptic nucleus. 2. Administration of omega‐agatoxin IVA (omega‐Aga IVA) blocked a high‐threshold non‐inactivating current. This current has an IC50 for omega‐Aga IVA of 3 nM; no other types of currents were blocked at doses of up to 500 nM. 3. In the axon terminals omega‐Aga IVA blocked a high‐threshold current that inactivates markedly (tau approximately 448 ms), and has a much lower sensitivity to the toxin, with an IC50 of 270 nM. Unlike the somatic current, the effect of omega‐Aga IVA in the terminals is largely prevented by omega‐conotoxin GVIA (omega‐CgTX). 4. These data suggest that MNC somata express a single type of omega‐Aga IVA‐sensitive calcium current similar to the P‐type calcium current described in other cells. However, the omega‐Aga IVA‐sensitive current in axon terminals differs from both the P‐type and the recently identified Q‐type current in that it is also sensitive to omega‐CgTX. The distinct biophysical properties of the currents in somata and axon terminals may have important physiological implications.