Effects of melatonin on ionic currents in cultured ocular tissues

1999 ◽  
Vol 276 (4) ◽  
pp. C923-C929 ◽  
Author(s):  
Adam Rich ◽  
Gianrico Farrugia ◽  
James L. Rae
Keyword(s):  
Epithelial Cells ◽  
Trabecular Meshwork ◽  
Cell Voltage ◽  
Ionic Currents ◽  
Lens Epithelial Cells ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Epithelial Cell Line ◽  
Voltage Dependent ◽  
Mouse Lens

The effects of melatonin on ionic conductances in a cultured mouse lens epithelial cell line (α-TN4) and in cultured human trabecular meshwork (HTM) cells were measured using the amphotericin perforated patch whole cell voltage-clamp technique. Melatonin stimulated a voltage-dependent Na+-selective current in lens epithelial cells and trabecular meshwork cells. The effects of melatonin were observed at 50 pM and were maximal at 100 μM. Melatonin enhanced activation and inactivation kinetics, but no change was observed in the voltage dependence of activation. The results are consistent with an increase in the total number of ion channels available for activation by membrane depolarization. Melatonin was also found to stimulate a K+-selective current at high doses (1 mM). Melatonin did not affect the inwardly rectifying K+ current or the delayed rectifier type K+ current that has been described in cultured mouse lens epithelial cells. The results show that melatonin specifically stimulated the TTX-insensitive voltage-dependent Na+ current by an apparently novel mechanism.

Ionic Currents Underlying Fast Action Potentials in the Obliquely Striated Muscle Cells of the Octopus Arm

2002 ◽  
Vol 88 (6) ◽  
pp. 3386-3397 ◽  
Author(s):  
Dan Rokni ◽  
Binyamin Hochner
Keyword(s):  
Time Constant ◽  
Action Potentials ◽  
Striated Muscle ◽  
Muscle Cells ◽  
Ionic Currents ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Activation Kinetics ◽  
Voltage Dependent ◽  
Neuromuscular Systems

The octopus arm provides a unique model for neuromuscular systems of flexible appendages. We previously reported the electrical compactness of the arm muscle cells and their rich excitable properties ranging from fast oscillations to overshooting action potentials. Here we characterize the voltage-activated ionic currents in the muscle cell membrane. We found three depolarization-activated ionic currents: 1) a high-voltage-activated L-type Ca2+ current, which began activating at approximately −35 mV, was eliminated when Ca2+ was substituted by Mg2+, was blocked by nifedipine, and showed Ca2+-dependent inactivation. This current had very rapid activation kinetics (peaked within milliseconds) and slow inactivation kinetics (τ in the order of 50 ms). 2) A delayed rectifier K+ current that was totally blocked by 10 mM TEA and partially blocked by 10 mM 4-aminopyridine (4AP). This current exhibited relatively slow activation kinetics (τ in the order of 15 ms) and inactivated only partially with a time constant of ∼150 ms. And 3) a transient A-type K+ current that was totally blocked by 10 mM 4AP and was partially blocked by 10 mM TEA. This current exhibited very fast activation kinetics (peaked within milliseconds) and inactivated with a time constant in the order of 60 ms. Inactivation of the A-type current was almost complete at −40 mV. No voltage-dependent Na+ current was found in these cells. The octopus arm muscle cells generate fast (∼3 ms) overshooting spikes in physiological conditions that are carried by a slowly inactivating L-type Ca2+ current.

Ion Channel Compartments in Photoreceptors: Evidence From Salamander Rods With Intact and Ablated Terminals

2007 ◽  
Vol 98 (1) ◽  
pp. 86-95 ◽  
Author(s):  
Peter R. MacLeish ◽  
Colin A. Nurse
Keyword(s):  
Ion Channels ◽  
Imaging Techniques ◽  
Cell Voltage ◽  
Ionic Currents ◽  
Simultaneous Recording ◽  
Delayed Rectifier ◽  
Sensory Cells ◽  
Before And After ◽  
Voltage Dependent ◽  
Highly Correlated

Vertebrate photoreceptors are highly polarized sensory cells in which several different ionic currents have been characterized. In the present study we used whole cell voltage-clamp and optical imaging techniques, the former combined with microsurgical manipulations, and simultaneous recording of membrane current and intracellular calcium signals to investigate the spatial distribution of ion channels within isolated salamander rods. In recordings from intact rods with visible terminals, evidence for five previously identified ionic currents was obtained. These include two Ca2+-dependent, i.e., a Ca2+-dependent chloride current [ ICl(Ca)] and a large-conductance Ca2+- and voltage-dependent K+ or BK current [ IK(Ca)], and three voltage-dependent currents, i.e., a delayed-rectifier type current [ IK(V)], a hyperpolarization-activated cation current ( Ih), and a dihydropyridine-sensitive L-type calcium current ( ICa). Of these, ICl(Ca) was highly correlated with the presence of a terminal; rods with visible terminals expressed ICl(Ca) without exception ( n = 125), whereas approximately 71% of rods (40/56) without visible terminals lacked ICl(Ca). More significantly, ICl(Ca) was absent from all rods ( n = 33) that had their terminals ablated, and recordings from the same cell before and after terminal ablation led, in all cases ( n =10), to the loss of ICl(Ca). In contrast, IK(Ca), IK(V), and Ih remained largely intact after terminal ablation, suggesting that they arose principally from ion channels located in the soma and/or inner segment. The outward IK(Ca) in terminal-ablated rods was reversibly suppressed on “puffing” a Ca2+-free extracellular solution over the soma and was appreciably enhanced by the L-type Ca2+ channel agonist, Bay K 8644 (0.1–2 μM). These data indicate that rod photoreceptors possess discrete targeting mechanisms that preferentially sort ion channels mediating ICl(Ca) to the terminal.

Mitomycin C-Induced Cell Death in Mouse Lens Epithelial Cells

2002 ◽  
Vol 34 (4) ◽  
pp. 213-219 ◽  
Author(s):  
Hyun-Kyung Park ◽  
Kwang-Won Lee ◽  
Jun-Sub Choi ◽  
Choun-Ki Joo
Keyword(s):  
Cell Death ◽  
Epithelial Cells ◽  
Mitomycin C ◽  
Lens Epithelial Cells ◽  
Mouse Lens

Effect of exogenous stress on the tissue-cultured mouse lens epithelial cells

2002 ◽  
Vol 86 (2) ◽  
pp. 302-306 ◽  
Author(s):  
Mihir Bagchi ◽  
Malkhan Katar ◽  
H. Maisel
Keyword(s):  
Epithelial Cells ◽  
Lens Epithelial Cells ◽  
Exogenous Stress ◽  
Mouse Lens

Cell kinetic status of mouse lens epithelial cells lacking αA- and αB-crystallin

2004 ◽  
Vol 265 (1/2) ◽  
pp. 115-122 ◽  
Author(s):  
Fang Bai ◽  
Jinghua Xi ◽  
Ryuji Higashikubo ◽  
Usha P. Andley
Keyword(s):  
Epithelial Cells ◽  
Lens Epithelial Cells ◽  
Cell Kinetic ◽  
Αb Crystallin ◽  
Mouse Lens

Differential expression of K+ currents in mammalian retinal bipolar cells

2002 ◽  
Vol 19 (2) ◽  
pp. 163-173 ◽  
Author(s):  
HUI-JUAN HU ◽  
ZHUO-HUA PAN
Keyword(s):  
Differential Expression ◽  
Cell Voltage ◽  
Bipolar Cells ◽  
Inactivation Kinetics ◽  
Voltage Dependent ◽  
Retinal Bipolar Cells ◽  
Kinetics Of ◽  
Retinal Cone ◽  
K Currents ◽  
Three Components

Whole-cell voltage-clamp recordings were performed to investigate voltage-dependent K+ currents in acutely isolated retinal cone bipolar cells (CBCs) from the rat. The physiological and pharmacological properties of the currents were compared with those in rod bipolar cells (RBCs). The K+ currents were found to be much larger in CBC than in RBCs. In addition, the currents in CBCs were activated and inactivated at more negative potentials. Based on the apparent inactivation property of the currents, CBCs were found to fall into two groups of cells that differed in the inactivation kinetics of IK(V) but did not correlate to the ON- and OFF-type. The IK(V) for the group of CBCs showing faster inactivation, as well as for all RBCs, contained two components with decay time constants around 0.1 and 1 s. The IK(V) for the group of CBCs showing slower inactivation only contained the slower component. Furthermore, three components of IK(V) were observed based on tetraethylammonium (TEA) sensitivity: high-sensitive, low-sensitive, and resistant component. The IK(V) for a portion of CBCs showing faster inactivation, as well as for all RBCs, contained all three components. The IK(V) for the remaining CBCs, including all of those CBCs showing slower inactivation, only contained the latter two components. This study reveals a differential expression of K+ currents in rat retinal bipolar cells, suggesting that K+ channels may play an important role in bipolar cell processing in mammalian retinas.

Changes in lens connexin expression lead to increased gap junctional voltage dependence and conductance

1995 ◽  
Vol 269 (3) ◽  
pp. C590-C600 ◽  
Author(s):  
P. J. Donaldson ◽  
Y. Dong ◽  
M. Roos ◽  
C. Green ◽  
D. A. Goodenough ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Gap Junction ◽  
Voltage Dependence ◽  
Expression Patterns ◽  
Fiber Cell ◽  
Lens Epithelial Cells ◽  
Connexin Expression ◽  
Fiber Cells ◽  
Gap Junctional ◽  
Mouse Lens

The differentiation of mouse lens epithelial cells into fiber cells is a useful model for studying the changes of the electrical properties of gap junction (cell-to-cell) channels that are induced by an alteration in connexin expression patterns. In this model, cuboidal lens epithelial cells differentiate into elongated fiber cells, and the expression of connexin43 (Cx43) in the epithelial cells is replaced with the production of high levels of Cx50 and Cx46 in the fiber cells. We now report a new procedure to isolate mouse lens fiber cell pairs suitable for double whole cell patch-clamp analysis. Analysis was also performed for fiberlike cell pairs differentiated from epithelial cells in culture. Voltage dependence and unitary conductance of fiber cell gap junction channels were determined and compared with the corresponding values previously measured for the channels joining lens epithelial cells and for lens connexin channels formed in Xenopus oocyte pairs. Our results support a differentiation-induced shift toward stronger gap junctional voltage dependence and larger unitary conductances in the fiber cells. Our data further reflect a balanced functional contribution of Cx50 and Cx46 in the fiber cell-to-cell channels rather than a predominance of a single connexin.

Characterization of macroscopic outward currents of canine colonic myocytes

1989 ◽  
Vol 257 (3) ◽  
pp. C461-C469 ◽  
Author(s):  
W. C. Cole ◽  
K. M. Sanders
Keyword(s):  
Outward Current ◽  
Cell Voltage ◽  
Muscle Cells ◽  
Time Dependent ◽  
Delayed Rectifier ◽  
Delayed Rectifier Current ◽  
Outward Currents ◽  
Voltage Dependent ◽  
K Current ◽  
Time Courses

Outward currents of colonic smooth muscle cells were characterized by the whole cell voltage-clamp method. Four components of outward current were identified: a time-independent and three time-dependent components. The time-dependent current showed strong outward rectification positive to -25 mV and was blocked by tetraethylammonium. The time-dependent components were separated on the basis of their time courses, voltage dependence, and pharmacological sensitivities. They are as follows. 1) A Ca2+-activated K current sensitive to external Ca2+ and Ca2+ influx was blocked by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (0.1 X 10(-3) M) and nifedipine (1 X 10(-6) and was increased by elevated Ca2+ (8 X 10(-6) M) and BAY K 8644 (1 X 10(-6) M). 2) A "delayed rectifier" current was observed that decayed slowly with time and showed no voltage-dependent inactivation. 3) Spontaneous transient outward currents that were blocked by ryanodine (2 X 10(-6) M) were also recorded. The possible contributions of these currents to the electrical activity of colonic muscle cells in situ are discussed. Ca2+-activated K current may contribute a significant conductance to the repolarizing phase of electrical slow waves.

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