A role for TREK1 in generating the slow afterhyperpolarization in developing starburst amacrine cells

Slow afterhyperpolarizations (sAHPs) play an important role in establishing the firing pattern of neurons that in turn influence network activity. sAHPs are mediated by calcium-activated potassium channels. However, the molecular identity of these channels and the mechanism linking calcium entry to their activation are still unknown. Here we present several lines of evidence suggesting that the sAHPs in developing starburst amacrine cells (SACs) are mediated by two-pore potassium channels. First, we use whole cell and perforated patch voltage clamp recordings to characterize the sAHP conductance under different pharmacological conditions. We find that this conductance was calcium dependent, reversed at EK, blocked by barium, insensitive to apamin and TEA, and activated by arachidonic acid. In addition, pharmacological inhibition of calcium-activated phosphodiesterase reduced the sAHP. Second, we performed gene profiling on isolated SACs and found that they showed strong preferential expression of the two-pore channel gene kcnk2 that encodes TREK1. Third, we demonstrated that TREK1 knockout animals exhibited an altered frequency of retinal waves, a frequency that is set by the sAHPs in SACs. With these results, we propose a model in which depolarization-induced decreases in cAMP lead to disinhibition of the two-pore potassium channels and in which the kinetics of this biochemical pathway dictate the slow activation and deactivation of the sAHP conductance. Our model offers a novel pathway for the activation of a conductance that is physiologically important.

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N-bromoacetamide removes a calcium-dependent component of channel opening from calcium-activated potassium channels in rat skeletal muscle.

The Journal of General Physiology ◽

10.1085/jgp.86.5.601 ◽

1985 ◽

Vol 86 (5) ◽

pp. 601-611 ◽

Cited By ~ 36

Author(s):

B S Pallotta

Keyword(s):

Skeletal Muscle ◽

Potassium Channels ◽

Voltage Dependence ◽

Calcium Sensitivity ◽

Rat Skeletal Muscle ◽

Open Probability ◽

Calcium Dependent ◽

Channel Opening ◽

Dependent Component ◽

Calcium Activated Potassium Channels

Calcium-activated potassium channels from cultured rat skeletal muscle were treated with the protein-modifying reagent N-bromoacetamide (NBA) (0.3-1 mM) and studied in excised patches using patch-clamp techniques. After NBA treatment, channels opened only occasionally, and, in contrast to untreated channels, the open probability was no longer sensitive to intracellular surface calcium ions (1 nM to 100 microM). Channel activity did, however, exhibit a voltage dependence similar in direction and magnitude to that shown before NBA treatment (increasing e-fold with 19 mV depolarization). Distributions of open channel lifetimes revealed that NBA treatment virtually abolished openings of long duration, which suggests that this class of openings requires calcium sensitivity. These effects were not reversed by subsequent washing. Quantitatively similar open probability, voltage dependence, and open-interval distributions were observed in untreated channels in calcium-free medium. These results suggest that NBA removed a calcium-dependent component of channel opening, and that normal channels are able to open in the absence of significant intracellular calcium concentrations.

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Calcium-activated potassium channels and nitric oxide coregulate estrogen-induced vasodilation

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.2000.279.1.h319 ◽

2000 ◽

Vol 279 (1) ◽

pp. H319-H328 ◽

Cited By ~ 71

Author(s):

Charles R. Rosenfeld ◽

Richard E. White ◽

Tim Roy ◽

Blair E. Cox

Keyword(s):

Nitric Oxide ◽

Heart Rate ◽

Potassium Channels ◽

Uterine Artery ◽

Single Channel ◽

Open Probability ◽

Calcium Dependent ◽

Calcium Activated Potassium Channels ◽

Artery Flow ◽

Oxide Synthase

Nitric oxide synthase (NOS) contributes to estradiol-17β (E2β)-induced uterine vasodilation, but additional mechanisms are involved, and the cellular pathways remain unclear. We determined if 1) uterine artery myocytes express potassium channels, 2) E2β activates these channels, and 3) channel blockade plus NOS inhibition alters E2β-induced uterine vasodilation. Studies of cell-attached patches identified a 107 ± 7 pS calcium-dependent potassium channel (BKCa) in uterine artery myocytes that rapidly increased single-channel open probability 70-fold ( P < 0.05) after exposure to 100 nM E2β through an apparent cGMP-dependent mechanism. In ovariectomized nonpregnant ewes ( n = 11) with uterine artery flow probes and catheters, local BKCa blockade with tetraethylammonium (TEA; 0.05–0.6 mM) dose dependently inhibited E2β-induced uterine vasodilation ( n = 37, R = 0.77, P < 0.0001), with maximum inhibition averaging 67 ± 11%. Mean arterial pressure (MAP) and E2β-induced increases ( P ≤ 0.001) in heart rate (13%) and contralateral uterine blood flow (UBF, ∼5-fold) were unaffected. Local NOS inhibition plus BKCa blockade, using submaximal doses of nitro-l-arginine methyl ester (5 mg/ml) and TEA (0.3 mM), did not alter basal UBF but completely inhibited ipsilateral E2β-induced uterine vasodilation without affecting MAP and E2β-induced increases in contralateral UBF and heart rate. Acute E2β-mediated uterine vasodilation involves rapid activation of uterine artery BKCa and NOS, and the pathway for their interaction appears to include activation of guanylyl cyclase.

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