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Direct actions of nitric oxide on rat neurohypophysial K + channels
Author(s) -
Ahern Gerard P.,
Hsu ShyueFang,
Jackson Meyer B.
Publication year - 1999
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.1469-7793.1999.00165.x
Subject(s) - chemistry , bk channel , mastoparan , nitric oxide , biophysics , posterior pituitary , biochemistry , membrane potential , g protein , pituitary gland , signal transduction , biology , organic chemistry , hormone
1 Nitric oxide (NO) has been shown to modulate neuropeptide secretion from the posterior pituitary. Here we show that NO activates large‐conductance Ca 2+ ‐activated K + (BK) channels in posterior pituitary nerve terminals. 2 NO, generated either by the photolysis of caged‐NO or with chemical donors, irreversibly enhanced the component of whole‐terminal K + current due to BK channels and increased the activity of BK channels in excised patches. NO also inhibited the transient A‐current. The time courses of these effects on K + current were very different; activation of BK channels developed slowly over several minutes whereas inhibition of A‐current immediately followed NO uncaging. 3 Activation of BK channels by NO occurred in the presence of guanylyl cyclase inhibitors and after removal of ATP or GTP from the pipette solution, suggesting a cGMP‐independent signalling pathway. 4 The sulfhydryl alkylating agent N ‐ethyl maleimide (NEM) increased BK channel activity. Pretreatment with NEM occluded NO activation. 5 NO activation of BK channels occurred independently of voltage and cytoplasmic Ca 2+ concentration. In addition, NO removed the strict Ca 2+ requirement for channel activation, rendering channels highly active even at nanomolar Ca 2+ levels. 6 These results suggest that NO, or a reactive nitrogen byproduct, chemically modifies nerve terminal BK channels or a closely associated protein and thereby produces an increase in channel activity. Such activation is likely to inhibit impulse activity in posterior pituitary nerve terminals and this may explain the inhibitory action of NO on secretion.