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Role of Q‐type Ca 2+ Channels in Vasopressin Secretion From Neurohypophysial Terminals of the Rat
Author(s) -
Wang Gang,
Dayanithi Govindan,
Kim Sinnei,
Hom Dennis,
Nadasdi Laszlo,
Kristipati Ramasharma,
Ramachandran J.,
Stuenkel Edward L.,
Nordmann Jean J.,
Newcomb Robert,
Lemos José R.
Publication year - 1997
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 - 10.1111/j.1469-7793.1997.351bk.x
Subject(s) - vasopressin , oxytocin , neurosecretion , neuropeptide , chemistry , free nerve ending , arginine , medicine , endocrinology , biophysics , biology , biochemistry , receptor , amino acid
1 The nerve endings of rat neurohypophyses were acutely dissociated and a combination of pharmacological, biophysical and biochemical techniques was used to determine which classes of Ca 2+ channels on these central nervous system (CNS) terminals contribute functionally to arginine vasopressin (AVP) and oxytocin (OT) secretion. 2 Purified neurohypophysial plasma membranes not only had a single high‐affinity binding site for the N‐channel‐specific ω‐conopeptide MVIIA, but also a distinct high‐affinity site for another ω‐conopeptide (MVIIC), which affects both N‐ and P/Q‐channels. 3 Neurohypophysial terminals exhibited, besides L‐ and N‐type currents, another component of the Ca 2+ current that was only blocked by low concentrations of MVIIC or by high concentrations of ω‐AgaIVA, a P/Q‐channel‐selective spider toxin. 4 This Ca 2+ current component had pharmacological and biophysical properties similar to those described for the fast‐inactivating form of the P/Q‐channel class, suggesting that in the neurohypophysial terminals this current is mediated by a ‘Q’‐type channel. 5 Pharmacological additivity studies showed that this Q‐component contributed to rises in intraterminal Ca 2+ concentration ([Ca 2+ ] i ) in only half of the terminals tested. 6 Furthermore, the non‐L‐ and non‐N‐component of Ca 2+ ‐dependent AVP release, but not OT release, was effectively abolished by the same blockers of Q‐type current. 7 Thus Q‐channels are present on a subset of the neurohypophysial terminals where, in combination with N‐ and L‐channels, they control AVP but not OT peptide neurosecretion.