Potassium Channels and Fluid Secretion

Physiology ◽  
1986 ◽  
Vol 1 (3) ◽  
pp. 92-95
Author(s):  
OH Peterson
Keyword(s):  
Potassium Channels ◽  
Patch Clamp ◽  
Single Channel ◽  
Acinar Cells ◽  
Fluid Secretion ◽  
Exocrine Glands ◽  
Great Precision ◽  
K Channels ◽  
Single Channel Currents ◽  
Channel Currents

Fluid secretion from exocrine glands can be switched on and off with great precision. Recent patch-clamp recordings of single-channel currents in acinar cells reveals that neurotransmitters and hormones control the opening of K+ channels. However, fluid secretion is due to transport of Na+ and Cl-, and movement of these ions occurs only when K+ can be transported simultaneously. Thus, by controlling K+ channels, neurotransmitters or hormones regulate Na+ and Cl-secretion.

Calcium-activated potassium channels and fluid secretion by exocrine glands

1986 ◽  
Vol 251 (1) ◽  
pp. G1-G13 ◽  
Author(s):  
O. H. Petersen
Keyword(s):  
Single Channel ◽  
Basolateral Membrane ◽  
Acinar Cells ◽  
Fluid Secretion ◽  
Exocrine Glands ◽  
K Channels ◽  
Luminal Membrane ◽  
Channel Opening ◽  
Cell Current ◽  
Cl Channels

Fluid secretion by exocrine glands is regulated by neurotransmitters and hormones. The secretagogues act on the acinar cells by switching on two types of conductance pathways: K+-selective channels in the basolateral membrane and Cl(-)-selective channels localized to the luminal membrane. The K+ channels have been quantitatively characterized in patch-clamp single-channel and whole-cell current-recording studies. Opening of the K+ channels is determined by the membrane potential (depolarization enhances the probability of channel opening), and the intracellular free Ca2+ concentration ([Ca2+]i) (a rise in [Ca2+]i increases the open-state probability). The Cl- channels are also controlled by internal Ca2+ in such a way that an elevation of [Ca2+]i favors opening. Secretagogues evoking an increase in [Ca2+]i activate both sets of channels causing a substantial loss of cellular KCl. KCl is taken up via a Na+-K+-2Cl- cotransport mechanism in the basolateral membrane and the Na+ uptake activates the Na+-K+ pump. In the steady-state stimulated situation the three basolateral transport proteins, the K+ channels, the Na+-K+ pump, and the Na+-K+-2Cl- cotransporter operate together as an electrogenic Cl- pump. Cl- exits into the lumen via the Ca2+-activated Cl- channels and Na+ follows through the paracellular shunt pathway. When stimulation of the acinar cells ceases the K+ and Cl- conductance pathways close and the Na+-K+ pump together with the Na+-K+-2Cl- cotransporter operate as a KCl pump, restoring the intracellular KCl lost initially after start of stimulation and secretion stops.

Potassium channels activated by GABAB agonists and serotonin in cultured hippocampal neurons

1994 ◽  
Vol 71 (6) ◽  
pp. 2570-2575 ◽  
Author(s):  
L. S. Premkumar ◽  
P. W. Gage
Keyword(s):  
Potassium Channels ◽  
Hippocampal Neurons ◽  
Single Channel ◽  
Gamma Aminobutyric Acid ◽  
Kinetic Behavior ◽  
Open Time ◽  
Voltage Dependent ◽  
Single Channel Currents ◽  
Channel Currents ◽  
Cultured Hippocampal Neurons

1. Single-channel currents were recorded in cell-attached patches on cultured hippocampal neurons in response to gamma-aminobutyric acid-B (GABAB) agonists or serotonin applied to the cell surface outside the patch area. 2. The channels activated by GABAB agonists and serotonin were potassium selective but had a different conductance and kinetic behavior. Channels activated by GABAB agonists had a higher conductance, longer open-time, and longer burst-length than channels activated by serotonin. 3. The kinetic behavior of channels activated by GABAB agonists varied with potential whereas channels activated by serotonin did not show voltage-dependent changes in kinetics. 4. In a few cell-attached patches, both types of channel were activated when the cell was exposed to GABA together with serotonin. 5. It was concluded that GABAB agonists and serotonin activate different potassium channels in the soma of cultured hippocampal neurons.

Recording of single γ-aminobutyrate- and acetylcholine-activated receptor channels translated by exogenous mRNA in Xenopus oocytes

1983 ◽  
Vol 218 (1213) ◽  
pp. 481-484 ◽  
Keyword(s):  
High Resolution ◽  
Patch Clamp ◽  
Xenopus Oocytes ◽  
Optic Lobe ◽  
Single Channel ◽  
Patch Clamp Recording ◽  
Chick Optic Lobe ◽  
Single Channel Currents ◽  
Channel Currents

High resolution (‘giga-seal’) patch clamp recording in Xenopus oocytes was used to measure single channel currents from ACh- and GABA-activated receptors. The proteins that make up these receptors had been translated from mRNA derived from, respectively, denervated cat muscle and chick optic lobe.

scholarly journals Tail End of the S6 Segment

2002 ◽  
Vol 120 (1) ◽  
pp. 87-97 ◽  
Author(s):  
Shinghua Ding ◽  
Richard Horn
Keyword(s):  
Potassium Channels ◽  
Energy Barrier ◽  
Single Channel ◽  
Noise Analysis ◽  
Selectivity Filter ◽  
Open Probability ◽  
Cytoplasmic Extension ◽  
Activation Gate ◽  
Single Channel Currents ◽  
Channel Currents

The permeation pathway in voltage-gated potassium channels has narrow constrictions at both the extracellular and intracellular ends. These constrictions might limit the flux of cations from one side of the membrane to the other. The extracellular constriction is the selectivity filter, whereas the intracellular bundle crossing is proposed to act as the activation gate that opens in response to a depolarization. This four-helix bundle crossing is composed of S6 transmembrane segments, one contributed by each subunit. Here, we explore the cytoplasmic extension of the S6 transmembrane segment of Shaker potassium channels, just downstream from the bundle crossing. We substituted cysteine for each residue from N482 to T489 and determined the amplitudes of single channel currents and maximum open probability (Po,max) at depolarized voltages using nonstationary noise analysis. One mutant, F484C, significantly reduces Po,max, whereas Y483C, F484C, and most notably Y485C, reduce single channel conductance (γ). Mutations of residue Y485 have no effect on the Rb+/K+ selectivity, suggesting a local effect on γ rather than an allosteric effect on the selectivity filter. Y485 mutations also reduce pore block by tetrabutylammonium, apparently by increasing the energy barrier for blocker movement through the open activation gate. Replacing Rb+ ions for K+ ions reduces the amplitude of single channel currents and makes γ insensitive to mutations of Y485. These results suggest that Rb+ ions increase an extracellular energy barrier, presumably at the selectivity filter, thus making it rate limiting for flux of permeant ions. These results indicate that S6T residues have an influence on the conformation of the open activation gate, reflected in both the stability of the open state and the energy barriers it presents to ions.

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