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Blocking K+ channels with TEA induces plasmalemma depolarization, increased [Ca2+]i, and ACTH secretion in AtT-20
1Department of Physiology, Oregon Health Sciences University, Portland 97201, USA.
Abstract:
Blocking K+ channels induces hormone secretion in various pituitary cell lines by a mechanism which is not completely delineated. In the present study, we employed the mouse pituitary tumor-derived AtT-20 cell as a model to evaluate this phenomenon. We correlated the effect of the K+ channel-blocker, tetraethylammonium (TEA), on K+ current and membrane potential utilizing whole cell recording, on cytosol Ca2+ ([Ca2+]i) concentration utilizing fura-2, and on ACTH secretion utilizing a perifusion system. TEA inhibited voltage-dependent K+ current and initiated membrane depolarization in a dose-dependent fashion. Divergences in the sensitivity to TEA between voltage-dependent K+ currents and membrane depolarization indicate that voltage-dependent K+ channels are not responsible for TEA-induced depolarization TEA (1-30 mM) also induced a concentration-dependent rise in [Ca2+]i concentration and ACTH secretion, both of which were inhibited by removing medium Ca2+. Our data indicate that TEA inhibits K+ currents and induces membrane depolarization; this opens Ca2+ channels in the plasmalemma, causing a rise in [Ca2+]i which initiates ACTH secretion. Alteration of K+ channel permeability by hormones or neurotransmitters may thus play an important regulatory role in controlling pituitary hormone secretion.
Insights
Blocking potassium (K+) channels with tetraethylammonium (TEA) triggers ACTH secretion in pituitary cells. This occurs via membrane depolarization, calcium influx, and subsequent hormone release, revealing a key regulatory mechanism.
Area of Science:
- Endocrinology
- Neuroscience
- Cell Biology
Background:
- Potassium (K+) channel blockade is known to induce hormone secretion in pituitary cells.
- The precise mechanism underlying this phenomenon remains incompletely understood.
Purpose of the Study:
- To investigate the mechanism by which K+ channel blockade by tetraethylammonium (TEA) induces ACTH secretion in AtT-20 mouse pituitary cells.
- To correlate the effects of TEA on K+ currents, membrane potential, intracellular calcium ([Ca2+]i), and ACTH release.
Main Methods:
- Whole-cell patch-clamp recording to measure K+ currents and membrane potential.
- Fura-2 fluorescence to quantify cytosolic Ca2+ ([Ca2+]i) concentration.
- Perifusion system to measure ACTH secretion.
Main Results:
- TEA inhibited voltage-dependent K+ currents and caused dose-dependent membrane depolarization.
- TEA induced a concentration-dependent increase in [Ca2+]i and ACTH secretion.
- Both TEA-induced [Ca2+]i rise and ACTH secretion were dependent on extracellular calcium.
Conclusions:
- TEA-induced pituitary hormone secretion is mediated by K+ channel blockade, membrane depolarization, and subsequent calcium influx.
- These findings highlight the critical role of K+ channel regulation in controlling pituitary hormone release.