This study is aimed to investigate the effects of high intracellular Mg²⁺ on L-type calcium channel in guinea-pig ventricular myocytes. The cardiomyocytes were acutely isolated with enzyme digestion method. By adopting inside-out configuration of patch clamp technique, single channel currents of the L-type calcium channel were recorded under different intracellular Mg²⁺ concentrations ([Mg²⁺]i). In control group, which was treated with 0.9 mmol/L Mg²⁺, the relative activity of calcium channel was (176.5 ± 34.1)% (n = 7). When [Mg²⁺]i was increased from 0.9 to 8.1 mmol/L (high Mg²⁺ group), the relative activities of calcium channel decreased to (64.8 ± 18.1)% (n = 6, P < 0.05). Moreover, under 8.1 mmol/L Mg²⁺, the mean open time of calcium channel was shortened to about 25% of that under control condition (P < 0.05), but the mean close time of calcium channel was not altered. These results suggest that high intracellular Mg²⁺ may inhibit the activities of L-type calcium channel, which is mainly due to the shortening of the mean open time of single L-type calcium channel.
Animals ; Calcium Channels, L-Type ; physiology ; Guinea Pigs ; Magnesium ; physiology ; Myocytes, Cardiac ; physiology ; Patch-Clamp Techniques

The variability of peak current of L-type calcium channel (I(Ca,L)) shows an increase in cardiomyocytes after 6 h of preservation when the acutely isolated cardiomyocytes are preserved in a small volume buffer solution. The mechanism of the increased variability of I(Ca,L) is not clear. In order to obtain more accurately and stably experimental data of I(Ca,L), the aim of this study was to observe the pH changes of preservation buffer solution with acutely isolated rat cardiomyocytes, and the effects of pH changes on the shape of cardiomyocytes, the function of mitochondria and the gating property of L-type calcium channel. The results indicated that the pH was kept stable in 100 mL buffer solution, but was decreased from 7.20 to 6.95 in 20 mL buffer solution during 10 h of cardiomyocyte preservation. Therefore, 100 mL or 20 mL preservation solution was used as a normal control or acidotic group, respectively. The ratio of abnormal to normal rod-shaped cardiomyocytes increased in the acidotic group after 6 h of preservation. The acidosis induced a reduction in mitochondrial membrane potential indicated by JC-1 fluorescent probe after 8 h of cardiomyocyte preservation. The acidosis also shifted the autofluorescence of NADPH from blue to green after 8 h of cardiomyocyte preservation. The above changes in mitochondrial function induced a significant decrease in the peak I(Ca,L) and a shift in the clamped voltage at peak I(Ca,L) from +10 mV to 0 mV, after 10 h of cardiomyocyte preservation. These results suggest that the best way to preserve acutely isolated cardiomyocytes is to use a larger volume buffer system. In order to get stable peak I(Ca,L), we need to not only select a normal shape of cardiomyocyte at a bright field but also a blue fluorescent myocyte at an ultraviolet excitation.
Animals ; Buffers ; Calcium Channels, L-Type ; physiology ; Cells, Cultured ; Membrane Potential, Mitochondrial ; Myocytes, Cardiac ; physiology ; Preservation, Biological ; Rats

OBJECTIVETo explore the modulatory effect of niflumic acid and blocker of calcium channel on the desensitization of gamma aminobutyric acid (GABA)-activated currents in dorsal root ganglion(DRG) neurons from rat.

METHODSThe whole-cell patch-clamp technique was used to observe the modulatory effect of niflumic acid and blocker of calcium channel on the desensitization of GABA-activated currents in neurons freshly dissociated from rat DRG neurons.

RESULTSApplication of GABA (0.1-1 000 micromol/L) could induce concentration-dependent inward currents in some cells (212/223, 95.11%). GABA-(100 micromol/L) activated currents was (1.32 +/- 0.74) nA (n = 84). However, pre-application of niflumic acid (1-100 micromol/L) and nitrendipine (specific blocker of L-calcium channel)(0.1-30 micromol/L) could inhibit the GABA-activated inward current which was identified to be GABAA receptor-mediated current. The inhibitory effects of niflumic acid and nitrendipine were concentration-dependent. The suppression rate of 10 micromol/L niflumic acid and nitrendipine to GABA-activated currents were (31.60% +/- 4.87%) (n = 19) and (43.60% < or = 5.10%) (n = 5), respectively. The desensitization of GABA-activated currents had double exponential characteristic. Tau value was (14.68 +/- 5.11) s (n = 6) and (175.8 +/- 42.67) s (n = 6, r = 0.9647), respectively. Pre-application of niflumic acid (100 micromol/L) and nickel chloride (nonspecific blocker of L-calcium channel) (100 micromol/L) altered tau value of the desensitization of GABA-activated currents, tau value reduced for (4.64 +/- 2.21) s (n = 3), (43.70 +/- 14.34) s ( n = 3, r = 0.9548) and (4.64 +/- 2.21) s (n = 3), (43.70 +/- 14.34) s (n = 3, r = 0.9721).

CONCLUSIONPre-application of niflumic acid exerts a more strong inhibitory effect on the peak value of GABA-activated current, which possibly is through blocking the calcium-activated chloride ion channel to accelerate the desensitization of GABA-activated currents.

Animals ; Animals, Newborn ; Calcium Channel Blockers ; pharmacology ; Calcium Channels, L-Type ; drug effects ; Ganglia, Spinal ; drug effects ; physiology ; Membrane Potentials ; drug effects ; physiology ; Neurons ; drug effects ; physiology ; Niflumic Acid ; pharmacology ; Nitrendipine ; pharmacology ; Patch-Clamp Techniques ; Rats ; Rats, Sprague-Dawley ; gamma-Aminobutyric Acid ; pharmacology

OBJECTIVETo investigate the molecular and functional changes in L-type Ca2+ channel of hypertrophied cardiomyocytes in neonatal rats induced by angiotensin II (Ang II).

METHODSThe in vitro model of cardiomyocyte hypertrophy was established in cultured cardiomyocytes from neonatal rats. Whole cell patch clamp was used to measure the L-type Ca2+ currents. Semi-quantitative RT-PCR was used to determine the mRNA expression of L-type Ca2+ channel alpha1C subunits.

RESULTSIn the hypertrophied cardiomyocytes induced by Ang II, I(Ca, L) densities were increased, whereas the features of I(Ca,L) activation, inactivation or recovery from inactivation were not affected. Meanwhile, Ang II increased the mRNA expression of L-type Ca2+ channel alpha1C subunits in cardiomyocytes. All these actions of Ang II could be blocked by the angiotensin II 1 type receptor blocker losartan.

CONCLUSIONDuring cardiomyocyte hypertrophy induced by Ang II, there are significant changes in the molecule and function of L-type Ca2+ channels, which are mediated by the angiotensin II 1 type receptor.

Angiotensin II ; adverse effects ; Animals ; Calcium ; metabolism ; Calcium Channels, L-Type ; metabolism ; Female ; Hypertrophy ; metabolism ; Male ; Membrane Potentials ; Myocytes, Cardiac ; metabolism ; pathology ; physiology ; Rats ; Rats, Sprague-Dawley

Action Potentials ; drug effects ; physiology ; Animals ; Cadmium ; toxicity ; Calcium Channels, L-Type ; physiology ; Myocytes, Cardiac ; drug effects ; physiology ; Rats ; Rats, Sprague-Dawley

PURPOSE: Despite the fact that desflurane prolongs the QTC interval in humans, little is known about the mechanisms that underlie these actions. We investigated the effects of desflurane on action potential (AP) duration and underlying electrophysiological mechanisms in rat ventricular myocytes. MATERIALS AND METHODS: Rat ventricular myocytes were enzymatically isolated and studied at room temperature. AP was measured using a current clamp technique. The effects of 6% (0.78 mM) and 12% (1.23 mM) desflurane on transient outward K+ current (I(to)), sustained outward current (I(sus)), inward rectifier K+ current (I(KI)), and L-type Ca2+ current were determined using a whole cell voltage clamp. RESULTS: Desflurane prolonged AP duration, while the amplitude and resting membrane potential remained unchanged. Desflurane at 0.78 mM and 1.23 mM significantly reduced the peak I(to) by 20+/-8% and 32+/-7%, respectively, at +60 mV. Desflurane (1.23 mM) shifted the steady-state inactivation curve in a hyperpolarizing direction and accelerated inactivation of the current. While desflurane (1.23 mM) had no effects on I(sus) and I(KI), it reduced the L-type Ca2+ current by 40+/-6% (p<0.05). CONCLUSION: Clinically relevant concentrations of desflurane appear to prolong AP duration by suppressing Ito in rat ventricular myocytes.
Action Potentials/*drug effects ; Anesthetics, Inhalation/*pharmacology ; Animals ; Calcium Channels, L-Type/physiology ; Heart Conduction System/drug effects/physiology ; Heart Ventricles/drug effects ; Isoflurane/*analogs & derivatives/pharmacology ; Myocardial Contraction/*drug effects/physiology ; Myocytes, Cardiac/*drug effects/physiology ; Patch-Clamp Techniques ; Potassium Channels/physiology ; Rats ; Rats, Sprague-Dawley

Voltage gated calcium channels (VGCCs) are multi-subunit membrane proteins present in a variety of tissues and control many essential physiological processes. Due to their vital importance, VGCCs are regulated by a myriad of proteins and signaling pathways. Here we review the literature on the regulation of VGCCs by proteolysis of the pore-forming α1 subunit, Ca(v)α(1). This form of regulation modulates channel function and degradation and affects cellular gene expression and excitability. L-type Ca(2+) channels are proteolyzed in two ways, depending on tissue localization. In the heart and skeletal muscle, the distal C-terminus of Ca(v)α(1) is cleaved and acts as an autoinhibitor when it reassociates with the proximal C-terminus. Relief of this autoinhibition underlies the β-adrenergic stimulation-induced enhancement of cardiac and skeletal muscle calcium currents, part of the "fight or flight" response. Proteolysis of the distal C-terminus of L-type channels also occurs in the brain and is probably catalyzed by a calpain-like protease. In some brain regions, the entire C-terminus of L-type Ca(2+) channels can be cleaved by an unknown protease and translocates to the nucleus acting as a transcription factor. The distal C-terminus of P/Q-channel Ca(v)α(1) is also proteolyzed and translocates to the nucleus. Truncated forms of the PQ-channel Ca(v)α(1) are produced by many disease-causing mutations and interfere with the function of full-length channels. Truncated forms of N-type channel Ca(v)α(1), generated by mutagenesis, affect the expression of full-length channels. New forms of proteolysis of VGCC subunits remain to be discovered and may represent a fruitful area of VGCC research.
Animals ; Calcium Channels, L-Type ; metabolism ; Calcium Signaling ; Humans ; Muscle, Skeletal ; physiology ; Proteolysis

BACKGROUNDEndometrial carcinoma is one of the most common female tract genital malignant tumors. Nifedipine, an L-type calcium channel antagonist can inhibit cell proliferation of carcinomas. Recent studies indicated that a rise in the free cytosolic calcium ([Ca(2+)](c)) was a potent inducer of autophagy. Here, we investigated the relationship between nifedipine and autophagy in Hec-1A cells.

METHODSCells were cultured with nifedipine (10 µmol/L) and harvested at different times for counting cell number. MTT assay was applied to evaluate the cell viability and transwell assay to reveal cell migration. Apoptotic cells were detected with annexin V/PI assay. Then cells were treated with 3-methyladenine (3-MA) (2.5 mmol/L) for 0, 5, 15, 30, 60, and 120 minutes and the expression of the L-type calcium channel alpha1D (Cav1.3) protein was detected. At last, cells were cultured and assigned to four groups with different treatment: untreated (control group), 10 µmol/L nifedipine (N group), 2.5 mmol/L 3-MA (3-MA group), and 10 µmol/L nifedipine plus 2.5 mmol/L 3-MA (N+3MA group). Autophagy was detected with GFP-LC3 modulation by fluorescent microscopy, and expression of the autophagy-associated proteins (LC3, Beclin1 and P70s6K) by Western blotting and monodansylcadaverine (MDC) labeled visualization.

RESULTSProliferation of Hec-1A cells was obviously suppressed by nifedipine compared with that of the untreated cells for 24, 48, and 96 hours (P = 0.000 for each day). The suppression of migration ability of the nifedipine-treated cells (94.0 ± 8.2) was significantly different from that of the untreated cells (160.00 ± 9.50, P = 0.021). The level of early period cell apoptosis induced by nifedipine was (2.21 ± 0.19)%, which was (2.90 ± 0.13)% in control group (P = 0.052), whereas the late period apoptosis level reached (10.38 ± 0.96)% and (4.40 ± 0.60)% (P = 0.020), respectively. The 3-MA group induced a slight increase in the Cav1.3 levels within 15 minutes, but significantly attenuated the Cav1.3 levels after 30 minutes. There were more autophagic vacuoles labeled by MDC in the N group (20.63 ± 3.36) than the control group (6.29 ± 0.16, P = 0.015). GFP-LC3 localization revealed that the LC3 levels of cells in 3-MA group, N+3MA group, 3-MA group were 2.80 ± 0.29, 2.30 ± 0.17, and 1.80 ± 0.21, respectively. Cells in the N group showed significant augmentation of autophagy (P < 0.05). Western blotting analysis confirmed the down-regulation of LC3 levels in 3-MA group (0.85 ± 0.21) and N+3MA group (1.21 ± 0.12) compared with nifedipine treatment (2.64 ± 0.15, P < 0.05). The annexin-V-FITC/PI assay showed that the level of early period cell apoptosis induced in the N+3-MA group ((11.22 ± 0.91)%) differed significantly from that of the control group ((2.51 ± 0.70)%) and N group ((3.47 ± 0.39)%). Similarly, the late period level of the N+3-MA group ((55.19 ± 2.51)%) differed significantly from that of the control group ((15.81 ± 1.36)%) and the N group ((22.09 ± 2.48)%, P < 0.05). The down-regulated expression of P70s6k and up-regulated expression of the Beclin1 revealed significant differences between the N+3-MA group and control group (P = 0.025; Beclin1: P = 0.015).

CONCLUSIONSProliferation and migration in vitro of endometrial carcinoma Hec-1A cells are significantly suppressed by nifedipine. The nifedipine leads autophagy to oppose Hec-1A cells apoptosis. Autophagy inhibition by 3-MA leads down-regulation of Cav1.3 and enhances nifedipine-induced cell death. The nifedipine-induced autophagy is linked to Beclin1 and mTOR pathways.

Adenine ; analogs & derivatives ; pharmacology ; Apoptosis Regulatory Proteins ; physiology ; Autophagy ; drug effects ; Beclin-1 ; Calcium ; metabolism ; Calcium Channel Blockers ; pharmacology ; Calcium Channels, L-Type ; physiology ; Cell Line, Tumor ; Endometrial Neoplasms ; drug therapy ; pathology ; Female ; Humans ; Membrane Proteins ; physiology ; Nifedipine ; pharmacology ; Signal Transduction ; physiology ; TOR Serine-Threonine Kinases ; physiology

OBJECTIVETo study the effect of salvianolic acid A (SAA) on L-type calcium current (I-CaL) in isolated ventricular myocytes of Sprague-Dawley rats.

METHODSSAA powder was dissolved in normal Tyrode's solution to reach the concentrations of 1, 10, 100, and 1000 μmol/L. The traditional whole-cell patch-clamp recording technique was employed to evaluate the effects of SAA on I-CaL in single ventricular myocytes which were prepared by Langendorff perfusion apparatus from Sprague-Dawley rats.

RESULTSSAA (1, 10, 100, and 1000 μmol/L) inhibited I-CaL peak value by 16.23%±1.3% (n=6, P<0.05), 22.9%±3.6% (n=6, P<0.05), 53.4%±3.0% (n=8, P<0.01), and 62.26%±2.9% (n=6, P<0.01), respectively. SAA reversibly inhibited I-CaL in a dose-dependent manner and with a half-blocking concentration (IC(50)) of 38.3 μmol/L. SAA at 100 μmol/L elevated the I-V curve obviously, and shifted the half-active voltage (V(0.5)) from (-15.78±0.86) mV to (-11.24 ±0.77) mV (n=6, P<0.05) and the slope (K) from 5.33±0.74 to 4.35±0.74 (n=6, P>0.05). However, it did not alter the shapes of I-V curve, steady-state inactivation curve, or recovery from inactivation curve.

CONCLUSIONSSAA inhibited I-CaL in a dose-dependent manner. It shifted the steady-state activation curve to a more positive voltage, which indicated that the drug affected the activated state of calcium channels, and suggested that the Ca(2+) antagonistic effect of SAA be beneficial in the treatment of myocardial ischemia reperfusion injury.

Animals ; Caffeic Acids ; chemistry ; pharmacology ; Calcium Channel Blockers ; chemistry ; pharmacology ; Calcium Channels, L-Type ; physiology ; Dose-Response Relationship, Drug ; Drugs, Chinese Herbal ; chemistry ; pharmacology ; Lactates ; chemistry ; pharmacology ; Myocardial Ischemia ; drug therapy ; physiopathology ; Myocytes, Cardiac ; drug effects ; physiology ; Patch-Clamp Techniques ; Rats ; Rats, Sprague-Dawley ; Reperfusion Injury ; drug therapy ; physiopathology

Some studies suggest that the calcium channels and rennin-angiotensin system (RAS) play pivotal roles in the region-specific vascular adaptation due to simulated weightlessness. This study was designed to clarify if angiotensin II (Ang II) was involved in the adaptational change of the L-type calcium channel (Ca(L)) in the cerebral arterial vascular smooth muscle cells (VSMCs) under simulated weightlessness. Tail suspension (SUS) for 3 d was used to simulate immediate early cardiovascular changes to weightlessness. Then VSMCs in cerebral basilar artery were enzymatically isolated using papain, and Ca(L) current (barium instead of calcium as current carrier) in VSMCs was measured by whole-cell patch-clamp techniques. The results showed that 3-day simulated weightlessness significantly increased current density of Ca(L). However, I-V relationships of normalized peak current densities and steady-state activation curves of Ca(L) were not affected by simulated weightlessness. Although Ang II significantly increased current densities of Ca(L) in both SUS and control rats, the increase of Ca(L) current density in SUS rats was much more than that in control rats. These results suggest that 3-day simulated weightlessness induces the adaptational change of Ca(L) in cerebral VSMCs including increased response to Ang II, indicating that Ang II may play an important role in the adaptational change of cerebral arteries under microgravity.
Adaptation, Physiological ; Angiotensin II ; physiology ; Animals ; Calcium Channels, L-Type ; physiology ; Cerebral Arteries ; cytology ; physiology ; Hindlimb Suspension ; Male ; Muscle, Smooth, Vascular ; cytology ; physiology ; Myocytes, Smooth Muscle ; metabolism ; physiology ; Rats ; Rats, Sprague-Dawley ; Time Factors ; Weightlessness Simulation