AIM: To determine the effect of hydrogen peroxide(H_2O_2) on voltage-gated potassium channel currents(IKv) in pulmonary vascular smooth muscle cells(PASMCs).METHODS: Using whole cell patch-clamp technique,IKv was recorded in freshly isolated rat PASMCs with acute enzymatic digestion method.The effect of hydrogen peroxide on IKv in PASMCs was investigated in normoxia.RESULTS: IKv in PASMCs was increased significantly by H_2O_2 and the increase depended on the concentration in normoxia.Current-voltage relationship curve shifted to the left.CONCLUSION: Hydrogen peroxide is an important K~+ channel opener.

AIMTo study the modulation of extracellular pH on the voltage-gated potassium currents (I(Kv)) in isolated pulmonary artery smooth muscle cells (PASMCs).

METHODSI(Kv) was recorded using whole-cell patch clamp technique under the external solutions with different pH. The electrophysiological characteristics of I(Kv) were then analyzed.

RESULTS(1) As compared to the normoxic group, I(K), decreased under acidic condition. When the extracellular pH were 7.0, 6.5, 6.0, the peak currents at a potential of +60 mV were inhibited by 16.93% +/- 2.47% (P < 0.01), 33.03% +/- 2.13% (P < 0.01), 41.59% +/- 6.53% (P < 0.01) respectively, and the current-voltage relationship (I/V) curve shifted to the right. (2) When the extracellular pH was 7.0, 6.5, 6.0, the voltage-depended Gk-Em was shifted to the direction of positive and the activation was sped up.

CONCLUSIONThe results suggest that with the development of hypoxic pulmonary vasoconstriction (HPV), extracellular pH may take part in the modulation of Kv channels partly, then make the cell depolarized and decrease the Kv currents, this will lead to open the L-type calcium channel and contract the pulmonary artery smooth muscle. It may be one of the mechanisms that hypoxic leads to HPV and finally accelerate the development of HPV.

Animals ; Hydrogen-Ion Concentration ; Male ; Muscle, Smooth, Vascular ; cytology ; Myocytes, Smooth Muscle ; metabolism ; physiology ; Patch-Clamp Techniques ; Potassium Channels, Voltage-Gated ; physiology ; Pulmonary Artery ; cytology ; metabolism ; physiology ; Rats ; Rats, Sprague-Dawley

In our studies, we have applied a novel tool, microelectrode arrays (MEA), to investigate the electrophysiological properties of murine embryonic hearts in vitro. The electrical signals were recorded from the areas of the heart adhering to the 60 MEA electrodes, being called field potentials (FPs). As an extracelluar recording, the waveform of the FP appeared similar to a reversed action potential obtained from single cell by whole cell current clamp and the FP duration was comparable with the action potential duration. To study propagation of spontaneous electrical activity, we have compared the occurrence time of FPs recorded from different electrodes. It is shown that there was already an apparent A-V delay [(50.21+/-9.7) ms] at day 9.5 post coitum (E9.5) when heart was still tubular-like and atrium and ventricle were not separated anatomically, while occurence of FP at different electrodes of ventricular area were almost synchronous. Further, we looked into the modulation of spontaneous electrical activity during cardiac development: at E9.5 of embryonic development, 1 mumol/L of isoproterenol (Iso) increased beating frequency by (34.04+/-7.31)%, shortened the A-V delay by (20.00+/-6.44) % and prolonged FP duration. In contrast, 1 mumol/L of carbachol (CCh) slowed down beating frequency by (42.32+/-5.36) %, A-V conduction by (26.00+/-4.81) % and shortened FP duration; however at late stage (E16.5), the regulatory effect of Iso and CCh was strengthened. Therefore we conclude that cardiac conduction system is already established at E9.5 when the four-chambered heart is not formed yet and the regulation of spontaneous activity by sympathetic and para-sympathetic system is gradually matured during cardiac development.
Action Potentials ; physiology ; Animals ; Electrophysiological Phenomena ; Fetal Heart ; physiology ; Heart Conduction System ; embryology ; physiology ; In Vitro Techniques ; Mice ; Microelectrodes

Whole-cell patch clamp recording was used to investigate the action of beta-amyloid peptide(1-40) (Abeta(1-40)) on high voltage-activated calcium channel current (I(HVA)) in acutely isolated hippocampal CA1 pyramidal neurons in rats and observe its modulation by ginkgolide B (GB). Drug was applied by extracellular bath or adding in the pipette solution, and its effect was determined by comparing the amplitude of I(HVA) before and after the drug application. Bath application of aggregated Abeta(1-40) at concentrations of 0.01~30 mumol/L increased the amplitude of I(HVA) in a dose-dependent manner by (5.43+/-3.01)% (n=8, P>0.05), (10.49+/-4.13) % (n=11, P>0.05), (40.69+/-8.01) % (n=16, P<0.01), (58.32+/-4.85) % (n=12, P<0.01), and (75.45+/-5.81) % (n=6, P<0.01), respectively, but had no effect on the I-V curve of I(HVA); fresh Abeta(1-40) almost had no effect on I(HVA) (n=5, P>0.05). L-type calcium channel antagonist nifedipine abolished the increase of I(HVA)by Abeta(1-40). The increase of I(HVA) by Abeta(1-40) (1.0 mumol/L) was enhanced to (66.19+/-5.74) % (P<0.05) by 8-Br-cAMP (membrane permeable analogue of cAMP) and to (73.21+/-6.90) % (P<0.05) by forskolin, an adenylyl cyclase (AC) agonist, and reduced to (20.08+/-2.18) % (P<0.05) by H-89, cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) antagonist. GB effectively inhibited the increase of I(HVA) by Abeta(1-40). The results indicate that Abeta(1-40) leads to an intracellular calcium overload by increasing I(HVA) via AC-cAMP-PKA. This may be one of the mechanisms for its neurotoxicity. GB can prevent neurons from neurotoxicity by inhibiting abnormal calcium influx caused by Abeta(1-40).
Amyloid beta-Peptides ; toxicity ; Animals ; Animals, Newborn ; Calcium Channels ; drug effects ; Ginkgolides ; pharmacology ; Hippocampus ; cytology ; metabolism ; Lactones ; pharmacology ; Neurons ; drug effects ; metabolism ; Neuroprotective Agents ; pharmacology ; Patch-Clamp Techniques ; Peptide Fragments ; toxicity ; Rats ; Rats, Wistar

For determination the ionic mechanisms of the hypoxic acclimatization at the level of channels, male Spradue-Dawley rats were divided into two groups: control normoxic group and chronic intermittent hypoxic group [O2 concentration: (10 +/-0.5)%, hypoxia 8 h a day]. Using whole cell patch-clamp technique, voltage-gated potassium channel currents (IK(V)) were recorded in freshly isolated pulmonary arterial smooth muscle cells (PASMCs) of rat with acute isolated method. The effect of acute hypoxia on IK(V) of PASMCs from chronic intermittent hypoxia group was investigated to offer some basic data for clarifying the ionic mechanisms of the hypoxic acclimatization. The results showed: (1) In control normoxic group, after acute hypoxia free-Ca(2+) solution, the resting membrane potential (Em) of PASMCs was depolarized significantly from -47.2+/-2.6 mV to -26.7+/-1.2 mV, and the IK(V) of PASMCs was decreased significantly from 153.4+/-9.5 pA/pF to 70.1+/-0.6 pA/pF, the peak current percent inhibition was up to (57.6+/-3.3)% at +60 mV, and current-voltage relationship curve shifted to the right. (2) In chronic intermittent hypoxic group, the IK(V) of PASMCs was decreased significantly by exposure to intermittent hypoxia in a time-dependent manner, appeared to start on day 10 and continued to day 30 (the longest time tested) of hypoxia, and current-voltage relationship curve shifted to the right in a time-dependent manner. (3) Compared with the control normoxic group, the percent IK(V) inhibition by acute hypoxia was significantly attenuated in the chronic intermittent hypoxia group and this inhibition effect declined with time exposure to hypoxia. The results suggest that K(V) inhibition was significantly attenuated by chronic intermittent hypoxia, and this effect may be a critical mechanism of the body hypoxic acclimatization.
Animals ; Cell Separation ; Hypoxia ; complications ; physiopathology ; Male ; Muscle, Smooth, Vascular ; cytology ; metabolism ; physiology ; Potassium Channels, Voltage-Gated ; antagonists & inhibitors ; Pulmonary Artery ; metabolism ; pathology ; Rats ; Rats, Sprague-Dawley

We isolated mouse embryonic cardiomyocytes derived from timed-pregnant females at different periods and used patch-clamp technique to investigate the muscarinic cholinergic modulation of pacemaker current I(f) in different developmental stages. In early development stage (EDS), muscarinic agonist carbachol (CCh) significantly decreased the magnitude of the pacemaker current I(f) but had no effect in late development stage (LDS). Forskolin (a direct adenylate cyclase activator) and IBMX (a non-selective phosphodiesterase inhibitor) increased I(f) in both EDS and LDS cells. Interestingly, although both forskolin and IBMX increased basal I(f), their effects on CCh-inhibited I(f) were different. Forskolin did not reverse the inhibitory action of CCh until intermediate development stage (IDS). In contrast, IBMX reversed the inhibitory action of CCh on I(f) in EDS but not in IDS. It is suggested that a decrease in intracellular cAMP is a possible mechanism for CCh to modulate I(f). During the EDS and IDS CCh controls the cytoplasmic cAMP level by different pathways: In EDS, CCh modulates I(f) possibly by activating PDE which accelerates the breakdown of cAMP, but in IDS possibly by inhibiting adenylate cyclase (AC) which then reduces the synthesis of cAMP.
Animals ; Carbachol ; pharmacology ; Colforsin ; metabolism ; pharmacology ; Female ; Heart ; embryology ; physiology ; Mice ; Muscarinic Agonists ; pharmacology ; Myocytes, Cardiac ; drug effects ; physiology ; Pacemaker, Artificial ; Phosphodiesterase Inhibitors ; metabolism ; pharmacology ; Pregnancy ; Receptors, Muscarinic ; metabolism