Voltage-dependent calcium channels in ventricular cells of rainbow trout: effect of temperature changes in vitro

2000 ◽  
Vol 278 (6) ◽  
pp. R1524-R1534 ◽  
Author(s):  
Catherine S. Kim ◽  
Mary D. Coyne ◽  
Judith K. Gwathmey
Keyword(s):  
Rainbow Trout ◽  
Calcium Channels ◽  
Temperature Sensitivity ◽  
Calcium Currents ◽  
Temperature Dependency ◽  
Patch Clamp Technique ◽  
Ventricular Cells ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels

Voltage-dependent calcium channels (VDCC) in ventricular myocytes from rainbow trout ( Oncorhynchus mykiss) were investigated in vitro using the perforated patch-clamp technique, which maintains the integrity of the intracellular milieu. First, we characterized the current using barium as the charge carrier and established the doses of various pharmacological agents to use these agents in additional studies. Second, we examined the current at several physiological temperatures to determine temperature dependency. The calcium currents at 10°C (acclimation temperature) were identified as l-type calcium currents based on their kinetic behavior and response to various calcium channel agonists and antagonists. Myocytes were chilled (4°C) and warmed (18 and 22°C), and the response of VDCC to varying temperatures was observed. There was no significant dependency of the current amplitude and kinetics on temperature. Amplitude decreased 25–36% at 4°C (Q10 ∼1.89) and increased 18% at 18°C (Q10 ∼1.23) in control, Bay K8644 (Bay K)-, and forskolin-enhanced currents. The inactivation rates (τi) did not demonstrate a temperature sensitivity for the VDCC (Q10 1.23–1.92); Bay K treatment, however, increased temperature sensitivity of τi between 10 and 18°C (Q10 3.98). The low Q10 values for VDCC are consistent with a minimal temperature sensitivity of trout myocytes between 4 and 22°C. This low-temperature dependency may provide an important role for sarcolemmal calcium channels in adaptation to varying environmental temperatures in trout.

The development of voltege-dependent ionic conductances In murine spinal cord neurones in culture

1988 ◽  
Vol 66 (10) ◽  
pp. 1328-1336 ◽  
Author(s):  
C. Krieger ◽  
T. A. Sears
Keyword(s):  
Spinal Cord ◽  
Sodium Current ◽  
Potassium Conductance ◽  
Calcium Currents ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Calcium Dependent ◽  
Ionic Conductances ◽  
Voltage Dependent

The development of voltage-dependent ionic conductances of foetal mouse spinal cord neurones was examined using the whole-cell patch-clamp technique on neurones cultured from embryos aged 10–12 days (E10–E12) which were studied between the first day in vitro (V1) to V10. A delayed rectifier potassium conductance (IK) and a leak conductance were observed in neurones of E10.V1, E11, V1, and E12, V1 as well as in neurones cultured for longer periods. A rapidly activating and inactivating potassium conductance (IA) was seen in neurones from E11, V2 and E12, V1 and at longer times in vitro. A tetrodotoxin (TTX) sensitive sodium-dependent inward current was observed in neurones of E11 and E12 from V1 onwards. Calcium-dependent conductances were not detectable in these neurones unless the external calcium concentration was raised 10- to 20-foid and potassium conductances were blocked. Under these conditions calcium currents could be observed as early as E11, V3 and E12, V2 and at subsequent times in vitro. The pattern of development of voltage-dependent ionic conductances in murine spinal neurones is such that initially leak and potassium currents are present followed by sodium current and subsequently calcium current.

scholarly journals Ascorbic acid modulation of calcium channels in pancreatic beta cells.

1993 ◽  
Vol 102 (3) ◽  
pp. 503-523 ◽  
Author(s):  
R V Parsey ◽  
D R Matteson
Keyword(s):  
Ascorbic Acid ◽  
Calcium Channels ◽  
Beta Cells ◽  
Pancreatic Beta Cells ◽  
Inactivation Kinetics ◽  
Dependent Manner ◽  
Patch Clamp Technique ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels ◽  
Metal Catalyzed

We have studied the effect of ascorbic acid on voltage-dependent calcium channels in pancreatic beta cells. Using the whole-cell and perforated-patch variants of the patch clamp technique to record calcium tail currents, we have shown that the slowly deactivating (SD) calcium channel, which is similar to the T-type channel in other cells, is inhibited in a voltage-dependent manner by ascorbic acid (AA). The other channels that carry inward current in beta cells, FD calcium channels and sodium channels, are unaffected by AA. Ascorbic acid causes a voltage-dependent decrease in the magnitude of the SD channel conductance which can be explained by the hypothesis that approximately 50-60% of the channels have their voltage dependence shifted by approximately 62 mV in the depolarizing direction. Thus, ascorbate appears to modify only a fraction of the SD channels. The activation kinetics of the ascorbate-modified channels are slower than control channels in a manner that is consistent with this hypothesis. Deactivation and inactivation kinetics are unaffected by ascorbate. These effects of ascorbate require metal ions, and it appears that some of the activity of ascorbate is due to a product of its metal catalyzed oxidation, perhaps dehydroascorbate.

Voltage-dependent calcium channels in rat midbrain dopamine neurons: modulation by dopamine and GABAB receptors

1995 ◽  
Vol 74 (3) ◽  
pp. 1137-1148 ◽  
Author(s):  
D. L. Cardozo ◽  
B. P. Bean
Keyword(s):  
Calcium Channels ◽  
Calcium Current ◽  
Receptor Agonist ◽  
Gabab Receptor ◽  
Calcium Currents ◽  
Dopamine Neurons ◽  
Gabab Receptors ◽  
High Threshold ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels

1. Voltage-dependent calcium channels were studied with whole cell voltage-clamp recordings from neurons enzymatically dispersed from the ventral mesencephalon of rat brains (postnatal days 3-10) and identified as dopamine neurons by 5,7-dihydroxytryptamine autofluorescence. 2. Dopamine neurons had large high-threshold calcium currents activated by depolarizations positive to -50 mV. Different components of calcium channel current were not readily distinguishable by voltage dependence or kinetics, but pharmacological experiments showed the existence of different channel types. The overall current had significant components blocked by nimodipine (28%), by omega-conotoxin GVIA (22%), and by omega-agatoxin-IVA (omega-Aga-IVA) (37%), and there was a significant amount of current (16%) remaining in saturating concentrations of all three blockers. 3. High-threshold calcium current was reversibly reduced by the gamma-aminobutyric acid-B (GABAB) receptor agonist baclofen and by dopamine and the D2 receptor agonist quinpirole. Inhibition by GABAB or dopamine agonists developed and reversed within seconds. 4. Quinpirole reduced both omega-conotoxin-sensitive and omega-Aga-IVA-sensitive components of calcium current. 5. With physiological ionic conditions, inward calcium currents were outweighed by outward currents, in part through calcium-activated potassium channels activated by omega-conotoxin-sensitive and omega-Aga-IVA-sensitive calcium entry.

Atrial natriuretic peptide differentially modulates T- and L-type calcium channels

1990 ◽  
Vol 258 (3) ◽  
pp. F473-F478 ◽  
Author(s):  
R. T. McCarthy ◽  
C. M. Isales ◽  
W. B. Bollag ◽  
H. Rasmussen ◽  
P. Q. Barrett
Keyword(s):  
Calcium Channels ◽  
Atrial Natriuretic Peptide ◽  
Natriuretic Peptide ◽  
Calcium Influx ◽  
Patch Clamp Technique ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels ◽  
Glomerulosa Cells ◽  
Channel Type ◽  
Atrial Natriuretic

Atrial natriuretic peptide (ANP) inhibits the secretion of aldosterone stimulated by any of these major physiological agonists: angiotensin II, adrenocorticotropic hormone, or K+. The stimulatory actions of each of these agonists depend on calcium influx through voltage-dependent calcium channels. Because two types of calcium channels have been previously described in bovine glomerulosa cells (T- and L-type), the patch-clamp technique was used to evaluate the effect of ANP on each voltage-dependent calcium channel type. ANP was found to differentially modulate these two channel types, stimulating L-current while inhibiting T-current. Inhibition of T-current resulted from a shift in the voltage dependence of inactivation to more negative potentials within the physiological range. These results indicate that the ANP-induced inhibition of aldosterone secretion may be partially mediated via a reduction of the calcium current through T-type channels.

Extracellular inhibition and intracellular enhancement of Ca2+ currents by Pb2+ in bovine adrenal chromaffin cells

1995 ◽  
Vol 74 (2) ◽  
pp. 574-581 ◽  
Author(s):  
L. R. Sun ◽  
J. B. Suszkiw
Keyword(s):  
Calcium Channels ◽  
Chromaffin Cells ◽  
Adrenal Chromaffin Cells ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Voltage Dependent Calcium Channels ◽  
Adrenal Chromaffin ◽  
Dose Dependent

1. Effects of highly neurotoxic, inorganic lead ions (Pb2+) on voltage-dependent calcium channels were investigated with the use of the whole cell patch-clamp technique in bovine adrenal chromaffin cells maintained in short-term primary culture (1–5 days). 2. Extracellularly applied Pb2+ induced a concentration-dependent, reversible inhibition of Ca2+ currents, with an estimated IC50 approximately equal to 3.0 x 10(-7) M free Pb2+. 3. Elevation of the intracellular free Ca2+ concentration above 10(-8) M dose-dependently reduced the amplitude of the initial Ca2+ current and increased the exponential rate of current rundown. 4. Intracellularly applied Pb2+ prevented the Ca(2+)-dependent reduction of the initial Ca2+ current amplitude and altered the current rundown kinetics from exponential to linear. The effect was dose dependent and saturable, with an estimated EC50 approximately equal to 2.0 x 10(-10) M free Pb2+. 5. These results indicate that in contrast to extracellular blockade, intracellular Pb2+ promotes Ca2+ currents by attenuating the Ca(2+)-dependent, steady-state inactivation of calcium channels. This provides a novel mechanism through which Pb2+ may disrupt calcium signaling in chronically lead-exposed cells.

Volatile Anesthetics Reduce Low-voltage-activated Calcium Currents in a Thyroid C-Cell Line

1996 ◽  
Vol 85 (5) ◽  
pp. 1167-1175 ◽  
Author(s):  
Thomas S. McDowell ◽  
Joseph J. Pancrazio ◽  
Carl III Lynch
Keyword(s):  
Calcium Channels ◽  
Cell Line ◽  
Low Voltage ◽  
Volatile Anesthetics ◽  
Calcium Currents ◽  
Whole Cell ◽  
Voltage Range ◽  
C Cell ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels

Background Volatile anesthetics may act in part by inhibiting voltage-dependent calcium channels. The effects of several volatile agents on three types of calcium channels in a thyroid C-cell line were examined. Methods Whole-cell calcium currents were recorded using standard patch clamp techniques. Current-voltage relationships were derived before, during, and after application of isoflurane, enflurane, or halothane. Low-voltage-activated (LVA; T type) calcium currents were isolated based on the voltage range of activation. High-voltage-activated (HVA) calcium currents were separated into L and N types using omega-conotoxin GVIA (omega-CTX) and nicardipine. Results All three agents reversibly decreased both LVA and HVA currents at clinically relevant concentrations. Isoflurane and enflurane both reduced peak LVA current more than peak HVA current: -33 +/- 6% (mean +/- SE) versus -22 +/- 4% for 0.71 mM isoflurane (n = 6), and -46 +/- 6% versus -35 +/- 5% for 1.21 mM enflurane (n = 6). In contrast, halothane depressed LVA and HVA currents to a similar extent: -22 +/- 4% versus -29 +/- 3% for 0.65 mM halothane (n = 6). Isoflurane had no effect on LVA whole-cell current kinetics. Pretreatment with either omega-CTX (400 nM) or nicardipine (1 microM) did not change the sensitivity of HVA current to isoflurane. Conclusions Isoflurane and enflurane block LVA calcium channels more potently than either L-type or N-type calcium channels, but halothane shows no such preferential effect. These results may have implications for the mechanism action of volatile anesthetics.

scholarly journals Agatoxin-IVA-Sensitive Calcium Channels Mediate the Presynaptic and Postsynaptic Nicotinic Activation of Cardiac Vagal Neurons

2001 ◽  
Vol 85 (1) ◽  
pp. 164-168 ◽  
Author(s):  
Jijiang Wang ◽  
Mustapha Irnaten ◽  
David Mendelowitz
Keyword(s):  
Calcium Channels ◽  
Calcium Channel ◽  
Calcium Channel Blocker ◽  
Channel Blocker ◽  
Patch Clamp Technique ◽  
Current Increase ◽  
Inward Current ◽  
Voltage Dependent Calcium Channel ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels

Whole cell currents and miniature glutamatergic synaptic events (minis) were recorded in vitro from cardiac vagal neurons in the nucleus ambiguus using the patch-clamp technique. We examined whether voltage-dependent calcium channels were involved in the nicotinic excitation of cardiac vagal neurons. Nicotine evoked an inward current, increase in mini amplitude, and increase in mini frequency in cardiac vagal neurons. These responses were inhibited by the nonselective voltage-dependent calcium channel blocker Cd (100 μM). The P-type voltage-dependent calcium channel blocker agatoxin IVA (100 nM) abolished the nicotine-evoked responses. Nimodipine (2 μM), an antagonist of L-type calcium channels, inhibited the increase in mini amplitude and frequency but did not block the ligand gated inward current. The N- and Q-type voltage-dependent calcium channel antagonists conotoxin GVIA (1 μM) and conotoxin MVIIC (5 μM) had no effect. We conclude that the presynaptic and postsynaptic facilitation of glutamatergic neurotransmission to cardiac vagal neurons by nicotine involves activation of agatoxin-IVA-sensitive and possibly L-type voltage-dependent calcium channels. The postsynaptic inward current elicited by nicotine is dependent on activation of agatoxin-IVA-sensitive voltage-dependent calcium channels.

scholarly journals Conflicting Nongenomic Effects of Progesterone in the Myometrium of Pregnant Rats

2021 ◽  
Vol 22 (4) ◽  
pp. 2154
Author(s):  
Katsuhiko Yasuda ◽  
Aya Yoshida ◽  
Hidetaka Okada
Keyword(s):  
Calcium Channels ◽  
Saline Solution ◽  
Contractile Activity ◽  
Time Dependent ◽  
Dependent Manner ◽  
Pregnant Rats ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels ◽  
Nongenomic Effects

Recently, it has been suggested that progesterone affects the contractile activity of pregnant myometrium via nongenomic pathways; therefore, we aimed to clarify whether progesterone causes and/or inhibits pregnant myometrial contractions via nongenomic pathways. Our in vitro experiments using myometrial strips obtained from rats at 20 days of gestation revealed that progesterone caused myometrial contractions in a concentration- and time-dependent manner at concentrations up to 5 × 10−7 M; however, this effect decreased at concentrations higher than 5 × 10−5 M. Similarly, progesterone enhanced oxytocin-induced contractions up to 5 × 10−7 M and inhibited contractions at concentrations higher than 5 × 10−5 M. Conversely, progesterone did not enhance high-KCl-induced contractions but inhibited contractions in a concentration- and time-dependent manner at concentrations higher than 5 × 10−7 M. We also found that RU486 did not affect progesterone-induced contractions or the progesterone-induced inhibition of high-KCl-induced contractions; however, progesterone-induced contractions were blocked by calcium-free phosphate saline solution, verapamil, and nifedipine. In addition, FPL64176, an activator of L-type voltage-dependent calcium channels, enhanced high-KCl-induced contractions and rescued the decrease in high-KCl-induced contractions caused by progesterone. Together, these results suggest that progesterone exerts conflicting nongenomic effects on the contractions of pregnant myometrium via putative L-type voltage-dependent calcium channels.

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