Distinct omega-agatoxin-sensitive calcium currents in somata and axon terminals of rat supraoptic neurones.
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.
Fisher
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TE
Centre for Research in Neuroscience, McGill University, Montreal, Quebec, Canada.
Bourque
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CW
D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects* / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D008297:Male; D018408:Patch-Clamp Techniques; D051381:Rats; D013111:Spider Venoms / Q000494:pharmacology*; D013495:Supraoptic Nucleus / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors; D020867:omega-Agatoxin IVA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D013111:Spider Venoms; D020867:omega-Agatoxin IVA