K(+) channels form a large family of membrane proteins that are expressed in a polarized fashion in any epithelial cell. Based on the transmembrane gradient for K(+) that is maintained by the Na(+)-K(+)-ATPase, these channels serve two principal functions for transepithelial transport: generation of membrane voltage and recycling of K(+). In this brief review, we will outline the importance of this ancient principle by examples of epithelial transport in the renal proximal tubule and gastric parietal cells. In both tissues, K(+) channel activity is rate-limiting for transport processes across the epithelial cells and essential for cell volume regulation. Recent experimental data using pharmacological tools and genetically modified animals have confirmed the original physiological concepts and specified the knowledge down to the molecular level. The development of highly active and tissue selective small molecule therapeutics has been impeded by two typical features of K(+) channels: their molecular architecture challenges the design of molecules with high affinity binding and they are expressed in a variety of tissues at the same time. Nevertheless, new insights into pathophysiology, e.g. that K(+) channel inhibition can block gastric acid secretion, render the clinical use of K(+) channel drugs in gastric disease and as kidney transport inhibitors highly attractive.
Animals ; Biological Transport ; Epithelial Cells ; physiology ; Kidney ; physiology ; Potassium ; Potassium Channels ; physiology ; Sodium-Potassium-Exchanging ATPase ; physiology

Inwardly rectifying potassium channels (Kir) are a special subset of potassium selective ion channels which pass potassium more easily into rather than out of the cell. These channels mediate a variety of cellular functions, including control of membrane resting potential, maintenance of potassium homeostasis and regulation of cellular metabolism. Given the existence of fifteen Kir genes in mammals, current genetic studies using mutant animals that lack a single channel may have missed many important physiological functions of these channels due to gene redundancy. This issue can be circumvented by using a simple model organism like Drosophila, whose genome encodes only 3 Kir proteins. The sophisticated genetic approaches of Drosophila may also provide powerful tools to identify additional regulation mechanisms of Kir channels. Here we provide an overview of the progress made in elucidating the function of Drosophila Kir channels. The knowledge of Drosophila Kir channels may lead us to uncover novel functions and regulation mechanisms of human Kir channels and help on pathological studies of related diseases.
Animals ; Drosophila ; physiology ; Membrane Potentials ; Potassium ; physiology ; Potassium Channels, Inwardly Rectifying ; physiology

Animals ; Asthma ; physiopathology ; Bronchi ; metabolism ; Bronchial Hyperreactivity ; etiology ; Humans ; Muscle, Smooth ; metabolism ; Potassium Channels ; chemistry ; physiology ; Potassium Channels, Calcium-Activated ; physiology ; Potassium Channels, Voltage-Gated ; physiology

AIMTo study the effect of Nociceptin/orphanin FQ (N/OFQ) on transient outward potassium (I(A)) in rat cerebral cortical neurons and its kinetic mechanism.

METHODSThe effects of N/OFQ on I(A) were investigated by using the whole cell patch clamp technique in acutely dissociated rat cerebral cortical neurons.

RESULTS(1) At the voltage of + 60 mV, 0.1 micromol/L N/OFQ made I(A) decreased from (5356.1 +/- 361.6) pA to (4113.3 +/- 312.7) pA (P < 0.01, n = 10) and the percent inhibition was 23.2% +/- 2.2%. (2) (N/OFQ made I-V curve of I(A) decreased significantly (P < 0.01, n = 10).(3) 0.1 micromol/L N/OFQ shifted the activation curve of I(A) to positive potential from (-9.2 +/- 2.5)mV to (30.6 +/- 3.7) mV (P < 0.01, n = 8) and changed the slope factor(kappa) of the activation curve from (20.4 +/- 2.3) mV to (22.6 +/- 2.1) mV (P > 0.05, n = 8). (4) 0.1 micromol/L N/OFQ caused a significant hyperpolarizing shift of the inactivation curve from (-64.1 +/- 3.2) mV to (-55.9 +/- 1.9) mV (P < 0.05, n = 5), without significant effect on kappa of the inactivation curve.

CONCLUSION0.1 micromol/L N/OFQ has a significant inhibition on I(A) and shift the activation and inactivation curve to depolarization in cerebral parietal cortical neurons of rats.

Animals ; Cerebral Cortex ; physiology ; Female ; Male ; Neurons ; physiology ; Opioid Peptides ; physiology ; Parietal Lobe ; physiology ; Potassium Channel Blockers ; Potassium Channels ; physiology ; Rats ; Rats, Wistar

Animals ; Cells, Cultured ; Electrophysiology ; Mice ; Mice, Inbred Strains ; Neurons ; physiology ; Potassium Channels ; physiology ; Spiral Ganglion ; physiology

The present study evaluated the effects of glyphosate on Pisum sativum germination as well as its effect on the physiology and biochemistry of germinated seedlings. Different physico-chemical biomarkers, viz., chlorophyll, root and shoot length, total protein and soluble sugar, along with sodium and potassium concentration, were investigated in germinated seedlings at different glyphosate concentrations. This study reports the influence of different concentrations of glyphosate on pea seeds and seedlings. Physicochemical biomarkers were significantly changed by glyphosate exposure after 15 days. The germination of seedlings under control conditions (0 mg/L) was 100% after 3 days of treatment but at 3 and 4 mg/L glyphosate, germination was reduced to 55 and 40%, respectively. Physiological parameters like root and shoot length decreased monotonically with increasing glyphosate concentration, at 14 days of observation. Average root and shoot length (n=30 in three replicates) were reduced to 14.7 and 17.6%, respectively, at 4 mg/L glyphosate. Leaf chlorophyll content also decreased, with a similar trend to root and shoot length, but the protein content initially decreased and then increased with an increase in glyphosate concentration to 3 mg/L. The study suggests that glyphosate reduces the soluble sugar content significantly, by 21.6% (v/v). But internal sodium and potassium tissue concentrations were significantly altered by glyphosate exposure with increasing concentrations of glyphosate. Biochemical and physiological analysis also supports the inhibitory effect of glyphosate on seed germination and biochemical effects on seedlings.
Biochemistry ; Biomarkers ; Chlorophyll ; Germination ; Peas ; Physiology ; Potassium ; Seedlings ; Sodium

Voltage-dependent potassium channels (Kv) are involved in proliferation and transformation in mammary epithelial cells. In previous studies, several groups have detected various potassium channels in breast cancer cells, and they assumed that potassium channels are related to the development of breast carcinoma, although the precise mechanisms are still unknown. We have previously reported that 4-aminopyridine (4-AP), one kind of potassium channel (K(+) channel) blocker, could affect the proliferation of MCF10A cells. The aim of the present study is to explore the expression and properties of K(+) channels in human mammary epithelial cells (MCF10A) and whether Kv channels are required for the proliferation of MCF10A cell. Electrophysiological, MTT analysis, PCR and Western blot methods were used to identify a K(+) conductance which is involved in tumorigenesis and not yet be described in MCF10A cells. A voltage-dependent, outward rectification and 4-AP-sensitive K(+) current was observed in these cells. The perfusion of 5 mmol/L 4-AP significantly decreased the amplitude of Kv current from (912.5+/-0.6) pA to (275+/-0.8) pA (n=5, P<0.01), when cells were recorded using 800 ms voltage steps from a holding potential of -60 mV to voltage ranging from -60 mV to +60 mV. PCR analysis demonstrated that Kv1.1, Kv1.2, Kv1.3, and Kv1.5 were all expressed in MCF10A and MCF7 cells. Furthermore, the expression of Kv1.5 was much higher in MCF10A than that in MCF7. Inhibitory effect of 4-AP on cell proliferation was dosage-dependent. Incubation with 5 mmol/L 4-AP reduced MCF10A cell proliferation to 25.29% in 48 h. Western blot analysis showed the activation of ERK1/2 which related to cell proliferation was enhanced, while p38 activation was decreased by 4-AP treatment for 10 min. These data provided the first evidence of the Kv channels expression in MCF10A cell and 4-AP could inhibit the proliferation of MCF10A through blocking the potassium channels, and the mechanism may be related to regulating the activity of different members of cell proliferation signaling pathway of MEK/ERK.
4-Aminopyridine ; pharmacology ; Cell Line ; Cell Proliferation ; Epithelial Cells ; physiology ; Humans ; Potassium Channel Blockers ; pharmacology ; Potassium Channels, Voltage-Gated ; physiology

Humans ; Potassium Channels, Inwardly Rectifying ; chemistry ; classification ; physiology ; Potassium Channels, Tandem Pore Domain ; chemistry ; classification ; physiology ; Protein Structure, Tertiary

BACKGROUNDAtrial fibrillation is a common arrhythmia with multi-factorial pathogenesis. Recently, a single nucleotide polymorphism (G/T) at position 1057 in the KCNE4 gene, resulting in a glutamic acid (Glu, E)/aspartic acid (Asp, D) substitution at position 145 of the KCNE4 peptide, was found in our laboratory to be associated with idiopathic atrial fibrillation (atrial fibrillation more frequent with KCNE4 145D). However, the functional effect of the KCNE4 145E/D polymorphism is still unknown.

METHODSWe constructed KCNE4 (145E/D) expression plasmids and transiently co-transfected them with the KCNQ1 gene into Chinese hamster ovary-K1 cells and performed whole-cell patch-clamping recording to identify the possible functional consequences of the single nucleotide polymorphism. Quantitative data were analyzed by Student;s t test. Probability values less than 0.05 were considered statistically significant.

RESULTSA slowly activating, non-inactivating voltage-dependent current ((24.0 +/- 2.9) pA/pF, at +60 mV)) could be recorded in the cells transfected with KCNQ1 alone. Co-expression of wild type KCNE4 inhibited the KCNQ1 current ((7.3 +/- 1.1) pA/pF)). By contrast, co-expression of KCNE4 (145D) augment the KCNQ1 current ((42.9 +/- 7) pA/pF)). The V(1/2) of activation for the KCNQ1/KCNE4 (145D) current was shifted significantly towards the depolarizing potential compared to that for the KCNQ1 current ((-2.3 +/- 0.2) mv vs (-13.0 +/- 1.5) mv, P < 0.01)) without changing the slope factorkappa. Furthermore, KCNE4 (145D) also affected the activation and deactivation kinetics of KCNQ1 channels.

CONCLUSIONWe provide experimental evidence that the KCNE4 (145E/D) polymorphism exerts the effect of "gain of function" on the KCNQ1 channel. It may underlie the genetic mechanism of atrial fibrillation. Further studies on the functional association between I(Ks) and KCNE4 (145D) polymorphism in cardiac myocytes are suggested.

Animals ; CHO Cells ; Cricetinae ; Cricetulus ; Humans ; KCNQ1 Potassium Channel ; physiology ; Polymorphism, Single Nucleotide ; Potassium Channels, Voltage-Gated ; analysis ; genetics ; physiology

The present study was carried out to determine the functional properties of Kv4.2 expressed in mammalian cells in comparison with native transient potassium outward current (I(A)) in the hippocampal neurons. Transient transfection, cell culture and whole cell voltage clamp techniques were used. The results showed that I(A) in cultured rat hippocampal neurons and Kv4.2 expressed in HEK293 cells both displayed "A"-type current properties. The activation curves of I(A) and Kv4.2 were better fitted by simple Boltzmann function with V(1/2) 10.0+/-3.3 mV, k 13.9+/-2.6 mV for I(A) and V1/2 -9.7+/-4.1 mV, k 15.8+/-5.7 mV for Kv4.2, respectively. The steady-state inactivation curves of I(A) had a midpoint of -93.0+/-11.4 mV and a slope of 9.0+/-1.5 mV. The voltage-dependence of inactivation for Kv4.2 exhibited midpoint and slope values of -59.4+/-12.2 mV and 8.0+/-3.1 mV, respectively. The time constants (tau) of recovery from inactivation of I(A) and Kv4.2 were 27.9+/-14.1 ms and 172.8+/-10.0 ms, respectively. These results suggest that Kv4.2 is probably a major isoform contributing to I(A) in hippocampus neurons.
Animals ; Animals, Newborn ; Cells, Cultured ; Female ; Gene Transfer Techniques ; Hippocampus ; metabolism ; physiology ; Ion Transport ; Male ; Neurons ; metabolism ; physiology ; Patch-Clamp Techniques ; Potassium Channel Blockers ; Potassium Channels ; genetics ; physiology ; Potassium Channels, Voltage-Gated ; Rats ; Rats, Wistar ; Shal Potassium Channels