[Effects of allapinin on sodium currents in isolated neurons of the trigeminal ganglia and cardiomyocytes of rats]. / Vliianie allapinina na natrievye toki izolirovannykh neironov trigeminal'nykh gangliev i kardiomiotsitov krys.

Block of sodium currents by allapinin (diterpene alkaloid with strong antiarrhythmic properties) was investigated in isolated, voltage clamped rat trigeminal neurons and cultured neonatal rat single ventricular myocytes. Allapinin produces a decrease in sodium current amplitude without any changes in voltage dependent properties. Possible differences between the mechanisms of antiarrhythmic effect of diterpene alkaloids and classic antiarrhythmic agents have been analysed.

[The use of thin slices of myocardium for recording the currents across single ion channels]. / Primenenie tonkikh srezov miokarda dlia registratsii tokov cherez odinochnye ionnye kanaly.

Thin cardiac slices (100-200 microns) from newborn (1-14 days old) rat heart ventricles were used for patch clamp recordings. High resistance seals (10-50 GOhms) between patch-clamp pipettes and the membrane of cardiac cells as well as classical patch-clamp configurations can be achieved on this preparation without any enzymatic treatment of tissue. Resisting potential for cardiac cells measured in whole-cell configuration ranged between -30 and -65 mV. Averaged sodium currents and single inward rectifying potassium elementary currents recorded in cell-attached mode displayed basic features similar to those previously reported for isolated rat ventricular cells. Application of the method described here in cardiac electrophysiology will allow patch-clamp studies on heart cells without the complicated procedures of cell isolation. In addition, the uncertainty associated with enzyme treatment can be avoided. In future, this technique could be a new tool for studying electrophysiological properties of heart cells in situ.

[The characteristics of the sodium currents across EGTA-modified calcium channels in the membrane of cultured rat cardiomyocytes]. / Kharakteristika natrievykh tokov cherez EGTA-modifitsirovannye kal'tsievye kanaly membrany kul'tiviruemykh kardiomiotsitov krys.

In isolated, cultured neonatal rat ventricular myocytes sodium currents through calcium channels induced by lowering of extracellular calcium concentration 100 nmol/l have been investigated by whole-cell patch clamp technique. Such Na(+)-carried currents are modulated by classic Ca2+ agonists and antagonists. The potential-dependent characteristics of Na+ current are shifted at 20 mV in hyperpolarizing direction as compared to initial Ca(2+)-carried current. The inactivation decay of Na+ current through Ca2+ channels has the monoexponential behaviour. The possible action of extracellular Ca2+ lowering on Ca2+ channel selective filter and gating mechanisms is suggested.

[Lack of low-threshold calcium channels in the membrane of cultured cells of the heart ventricle of newborn rats]. / Otsutstvie nizkoporogovykh kal'tsievykh kanalov b membrane kul'tiviruemykh kletok zheludochka serdtsa novorozhdennykh krys.

In isolated, cultured neonatal rat ventricular myocytes calcium current was investigated by whole-cell patch clamp technique. The shift of holding potential values from -100-80 mV to -40 mV caused no significant changes in calcium current potential-dependent and kinetic properties. No calcium current component with preferential steady-state inactivation at membrane potentials ranged between -100 and -60 mV was observed. Calcium current component resistant to classic Ca-antagonists action was not found either. All data listed above permit a conclusion on lack of the low-threshold calcium channels in the membrane of single cultured neonatal rat ventricular myocytes. Possible reasons of the absence of this type of calcium are discussed.

[2 components of the high-threshold calcium current possessing different sensitivities to omega-conotoxin in the membrane of pheochromocytoma cells]. / Dva komponenta vysokoporogovogo kal'tsievogo toka, obladaiushchie raznoi chuvstvitel'nost'iu k omega-konotoksinu, v membrane kletok feokhromotsitomy.

Blockade of the high-threshold calcium currents by omega-conotoxin (CgTx) was investigated by patch-clamp recordings of whole-cell currents in cultured cells of pheochromocytoma PC12. CgTx (10 mumol/l) preferentially blocked only a steady-state component of the calcium current. Inactivated component was insensitive to CgTx (up to 50 mumol/l concentration). The two component nature of the high-threshold calcium current in pheochromocytoma PC12 cells was suggested.

[The effect of allapinine on the sodium currents of isolated trigeminal ganglion neurons and cardiomyocytes of rats]. / Vliianie allapinina na natrievye toki izolirovannykh neironov trigeminal'nogo gangliia i kardiomiotsitov krys.

Block of sodium currents by allapinine (diterpene alkaloid with strong antiarrhythmic properties) was investigated in isolated, voltage-clamped trigeminal neurons of a rat and single ventricular myocytes of a neonatal rat. Allapinine (in micromolar concentrations) produced a 70-90% decrease of the sodium current amplitude without any changes in voltage-dependent properties of INa in both neurons and cardiomyocytes. Allapinine also blocked the aconitine-modified sodium current. An increase of depolarization frequencies (0.5 to 5.0 Hz) produced no additional block of sodium currents in allapinine-bathed neurons and ventricular myocytes.

[The effect of the acidification of the extracellular medium on the membrane sodium currents of single heart cells]. / Vliianie zakisleniia vnekletochnoi sredy na natrievye toki membrany odinochnykh kletok serdtsa.

The effect of a drop of extracellular pH on the fast and slow sodium currents (INaf and INas) was studied in the rat isolated perfused ventricular myocytes. The shift of the extracellular pH value from 7.4 to 5.0 caused a disappearance of INaf. If the fast sodium current was blocked by external tetrodotoxin (10(-6) mol/l) or inactivated by the shift of the maintaining potential from -120 to -70 mV. the external pH drop from 7.4 to 5.0 only caused a slight diminishing of the slow sodium current amplitude. INas kinetics and potential-dependent properties were unaffected. INas was blocked at the external pH values lower than 4.0. The data obtained suggests that INaf and INas of isolated single cardiomyocytes have a different sensitivity to external pH: INaf is more sensitive to the acidification of the external medium than INas.

[Use of a microfluorometric method for measuring free calcium in the cytoplasm of isolated cultured rat cardiomyocytes]. / Primenenie metoda mikrofliuorometrii dlia izmereniia svobodnogo ka'ltsiia v tsitoplazme odinochnykh ku'ltiviruemykh kardiomiotsitov krysy.

Dual wavelength microfluorometry was used to measure the cytoplasmic free calcium concentration [( Ca2+]in) in single cultured cells from ventricular myocytes of neonatal rats loaded with the indicator fura-2. At 2.5 nmol/l extracellular Ca2+ in the resting cells [Ca2+]in was between 80 and 110 nmol/l. Sometimes, spontaneous low-frequency (approximately 0.1 Hz) [Ca2+]in oscillations were observed. High-potassium depolarization led to a Ca2+-antagonists-sensitive rise of [Ca2+]in. Both caffeine++ (5-10 mmol/l) and thymol (lmmol/l) initialized transient increase of [Ca2+]in. Mechanisms of [Ca2+]in homeostasis in heart muscle cells were discussed.

[Effect of reduced extracellular level of sodium ions on the intracellular level of calcium ions in the cytoplasm of cultured rat cardiomyocytes]. / Vliianie snizheniia vnekletochnoi kontsentratsii ionov natriia na vnutrikletochnuiu kontsentratsiiu ionov ka'ltsiia v tsitoplazme ku'ltiviruemykh kardiomiotsitov krys.

Cytosolic free calcium [( Ca2+]in) was measured using fura-2 in isolated cultured ventricular myocytes of neonatal rat. Exposure of the cardiomyocyte to a solution in which all Na+ have been replaced by impermeable cations results in a 400-600 nmol/l increase of [Ca2+]in. This increase is followed by a slow decrease to the initial level. A decrease of the extracellular calcium concentration from 2.5 to 0.5 mmol./l or increase to 10 mmol/l produced, respectively, decrease and increase of the amplitude of [Ca2+]in rise in response to low-Na+ superfusion. Exposure of cardiomyocytes to low-Na+ solutions also led to a 2-3 fold increase of caffeine++-dependent Ca2+ release from intracellular stores. Changes in [Ca2+]in can be attributed to the operation of a sodium-calcium exchanger in heart cells.

[Frequency-related blocking of sodium channels in the membrane of isolated rat cardiomyocytes by the calcium antagonist verapamil]. / Chastotno-zavisimoe blokirovanie natrievogo toka membrany izolirovannykh kardiomiotsitov krys kal'tsievym antagonistom verapamilom.

Use-dependent blocking of sodium current in the membrane of single rat cardiomyocytes by verapamil (in the concentration range of 5-50 mumol/l) has been observed. The data obtained suggest that verapamil binding with sodium channels which are in the open or inactivated state underlies suppression of sodium current.