Study of transmembrane La^(3+) movement in rat ventricular myocytes by the patch-clamp technique

We have studied transmembrane La3+ movement in rat ventricular myocytes for the first time by using the whole-cell patch-clamp recording mode. La3+ (0.01-5.0 mmol/L) could not bring out inward currents through the L-type calcium channel in rat ventricular myocytes, while it could enter the cells by the same way carried by 1μmo1/L ionomycin. When the outward Na+ concentration gradient is formed, La3+ can enter the cells via Na-Ca exchange, and the exchange currents increase with the increase of external La3+ concentrations. But compared with Na-Ca exchange currents in the same concentration, the former is only 14%-38% of the latter. The patch-clamp experiment indicates that La3+ normally can not enter ventricular myocytes through L-type calcium channel, but it can enter the cells via Na-Ca exchange.

Effects of antigliomatin from the scorpion venom of Buthus martensii Karsch on chloride channels on C6 glioma cells

Using whole-cell patch-clamp recordings, the effects of antigliomatin were observed on chloride channels on C6 glioma cells cultured in vitro. Antigliomatin was extracted from the venom of the scorpion Buthus martensii Karsch. Chloride channels are closed under normal osmotic pressure. When osmotic pressure was reduced to 120, 110 and 100 mV, the cell volume enlarged, chloride channels opened, and the chloride channel current increased. Three minutes after antigliomatin treatment, the chloride channel current decreased in a dose-dependent manner. These results show that antigliomatin extracted from the venom of the scorpion Buthus martensii Karsch diminishes chloride channel currents on C6 glioma cells.

Spontaneous firing properties of rat medial vestibular nucleus neurons in brain slices by infrared visual patch clamp technique

Domestic application of infrared patch clamp techniques on brain slices is limited.The key of the tech-nique is to prepare high-quality brain slices.The present paper describes the preparation procedure of brainstem slices and the spontaneous firing properties of rat medial vestibular nucleus(MVN)neurons.By infrared differ-ential interference contrast technique,neurons of rat MVN were visualized directly at the depth of 50–100 mm underneath the surface of slices.Firing activities of MVN neurons were recorded by the whole-cell patch clamp technique in artificial cerebrospinal fluid(ACSF)and low Ca^(2+)-high Mg^(2+) fluid.The firing mode was more irregular and depressive in low Ca^(2+)-high Mg2+fluid than in ACSF.According to the averaged waveform of action potentials,cells were classified as the neurons with mono-phasic after-hyperpolarization potential(AHP),and the neurons with biphasic AHP.The resting membrane potential(RMP),input resistance(Rin)and membrane capacitance(Cm)of neurons were recorded and com-pared between groups.With infrared videomicroscopy,patch clamp recordings could be made under direct obser-vation in freshly prepared brainstem slices.The discharge activities of MVN neurons were spontaneous and the fir-ing mode was modulated by extracellular calcium concen-tration.The basic membrane properties of two types of neurons were not significantly different,while the differ-ences in waveform might play a role in the segregation between tonic and kinetic cells.

Rapid effect of stress concentration corticosterone on glutamate receptor and its subtype NMDA receptor activity in cultured hippocampal neurons

Objective: To study the rapid effect of glucocorticoids (GCs) on NMDA receptor activity in hippocampal neurons in stress and to elucidate its underlying probable membrane mechanisms. Methods: Whole-cell patch-clamp recording was used to assess the effect of stress concentration corticosterone (B) on the responses of cultured hippocampal neurons to glutamate and NMDA (N-methy-D-asparatic acid). To make clear the target of B, intracellular dialysis of B(10 μmol/L)through patch pipette and extracellular application of bovine serum albumin-conjugated corticosterone(B-BSA, 10 μmol/L)were carried out to observe their influence on peak amplitude of NMDA-evoked current. Results: B had a rapid, reversible and inhibitory effect on peak amplitude of GLU- or NMDA-evoked current in cultured hippocampal neurons. Furthermore, B-BSA had the inhibitory effect on INMDA as that of B, but intracellularly dialyzed B had no significant effect on I NMDA. Conclusion: These results suggest that under the condition of stress, GCs may rapidly, negatively regulate excitatory synaptic receptors-glutamate receptors (GluRs), especially NMDA receptor (NMDAR) in central nervous system, which is mediated by rapid membrane mechanisms, but not by classical, genomic mechanisms.

Protein Kinase C Enhances the Swelling-Induced Chloride Current in Human Atrial Myocytes

Swelling-activated chloride currents（ICl.swell） are thought to play a role in several physiologic and pathophysiologic processes and thus represent a target for therapeutic approaches. However, the mechanism of ICl.swell regulation remains unclear. In this study, we used the whole-cell patch-clamp technique to examine the role of protein kinase C（PKC） in the regulation of ICl.swell in human atrial myocytes. Atrial myocytes were isolated from the right atrial appendages of patients undergoing coronary artery bypass and enzymatically dissociated. ICl.swell was evoked in hypotonic solution and recorded using the whole-cell patch-clamp technique. The PKC agonist phorbol dibutyrate（PDBu） enhanced ICl.swellin a concentration-dependent manner, which was reversed in isotonic solution and by a chloride current inhibitor, 9-anthracenecarboxylicacid. Furthermore, the PKC inhibitor bis-indolylmaleimide attenuated the effect and 4α-PDBu, an inactive PDBu analog, had no effect on ICl.swell. These results, obtained using the whole-cell patch-clamp technique, demonstrate the ability of PKC to activate ICl,swell in human atrial myocytes. This observation was consistent with a previous study using a single-channel patch-clamp technique, but differed from some findings in other species.

Pathological Networks Involving Dysmorphic Neurons in Type ⅡFocal Cortical Dysplasia

Focal cortical dysplasia(FCD)is one of the most common causes of drug-resistant epilepsy.Dysmorphic neurons are the major histopathological feature of typeⅡFCD,but their role in seizure genesis in FCD is unclear.Here we performed whole-cell patch-clamp recording and morphological reconstruction of cortical principal neurons in postsurgical brain tissue from drug-resistant epilepsy patients.Quantitative analyses revealed distinct morphological and electrophysiological characteristics of the upper layer dysmorphic neurons in typeⅡFCD,including an enlarged soma,aberrant dendritic arbors,increased current injection for rheobase action potential firing,and reduced action potential firing frequency.Intriguingly,the upper layer dysmorphic neurons received decreased glutamatergic and increased GABAergic synaptic inputs that were coupled with upregulation of the Na^(+)-K^(+)-Cl^(−)cotransporter.In addition,we found a depolarizing shift of the GABA reversal potential in the CamKⅡ-cre::PTENflox/flox mouse model of drug-resistant epilepsy,suggesting that enhanced GABAergic inputs might depolarize dysmorphic neurons.Thus,imbalance of synaptic excitation and inhibition of dysmorphic neurons may contribute to seizure genesis in typeⅡFCD.

Pertussis toxin modulation of sodium channels in the central neurons of cyhalothrin-resistant and cyhalothrinsusceptible cotton bollworm, Helicoverpa armigera

Pertussis toxin （FIX） inhibits the activation of the α-subunit of the inhibitory heterotrimeric G-proteins （Cαi/o） and modulates voltage-gated sodium channels, which may be one of the primary targets of pyrethroids. To investigate the potential mechanisms of agricultural pests resistance to pyrethroid insecticides, we examined the modulations by PTX on sodium channels in the central neurons of the 3rd-4th instar larvae of cyhalothrin-resistant （Cy-R） and cyhaiothrin-susceptible （Cy-S） Helicoverpa armigera by the whole-cell patch-clamp technique. The isolated neurons were cultured for 12-16 h in an improved L15 insect culture medium with or without PTX （400 ng/mL）. The results showed that both the Cy-R and Cy-S sodium channels exhibited fast kinetics and tetrodotoxin （TTX） sensitivity. The Cy-R sodium channels exhibited not only altered gating properties, including a 8.88-mV right shift in voltage-dependent activation （V0.5act） and a 6.54-mV right shift in voltage-dependent inactivation （V0.5inact）, but also a reduced peak in sodium channel density （Ⅰdensity） （55.2% of that in Cy-S neurons）. Cy-R sodium channels also showed low excitability, as evidenced by right shift of activation potential （Ⅴacti） by 5-10 mV and peak potential （Ⅴpcak） by 20 mV. FIX exerted significant effects on Cy-S sodium channels, reducing sodium channel density by 70.04%, right shifting V0.5act by 14.41 mV and V0.5inact by 9. 38 mV. It did not cause any significant changes of the parameters mentioned above in the Cy-R sodium channels. The activation time （Tpeak） from latency to peak at peak voltage and the fast inactivation time constant （τinact） in both Cy-S and Cy-R neurons were not affected. The results suggest that cotton bollworm resistant to pyrethroid insecticides involves not only mutations and allosteric alterations of voltage-gated sodium channels, but also might implicate perturbation of PTX-sensitive Gαi/o-COupled signaling Wansduction pathways.