[Possible participation of slow Na+--Ca++ channels in realizing cholinergic effects on the cardiac pacemaker]. / O vozmozhnosti uchastii medlennykh Na+--Ca++ kanalov v realizatsii kholinergicheskikh vliianii na voditel' ritma serdtsa.

The effect of the Ca++-permeability inhibitors (Mn ions, Verapamil, D-600) on the bioelectrical activity and cholinergic responses of isolated sinus node involved reduction of the pacemaker rhythm within 30-40 min and a complete inhibition of the bioelectrical discharge as well as a diminished amplitude of the AP and a reduced slope of the slow diastolic and the fast depolarization. The findings seem to be due to an inhibiting of the slow Na+-Ca++ influx by Ca++-antagonists. The prolonged APs and the reduced rate of terminal repolarization might be due to effect of the inhibition on potassium permeability. After electrical stimulation of the efferent nerve or acetylcholine application, the cholinergic reactions were markedly reduced with Mn++ D-600 and Verapamil. The participation of slow Na+-Ca++ channels in cholinergic reactions of pacemaker cells is discussed.

[Photooxidation and light-induced transport of phenazine methosulfate in chromatophores of purple bacteria]. / Fotookislenie i fotoindutsirovannyi transport fenazinmetosul'fata v khromatoforakh purpurnykh bakterii.

The light-induced interaction of phenazine methosulfate (PMS) with chromatophores of the purple bacteria Rhodospirillum rubrum and Rhodopseudomonas sphaeroides was studied, using an ion-specific electrode. Illumination caused an initial rapid increase in the concentration of methylphenazinium cation (MP+) and a subsequent slow (1-3 min) decrease of the MP+ concentration to a low steady level. The rapid phase of the light-induced MP+ concentration change is specifically enhanced by ascorbate. The slow phase (uptake of MP+ from the medium) is stimulated on addition of valinomycin, which is known to collapse the membrane potential of energized chromatophores, and is partly inhibited by NH4Cl, which enhances the membrane potential in chromatophores. The light-induced uptake of MP+ is sharply stimulated by dibromothymoquinone. It is concluded that the initial rapid increase of the MP+ concentration in the outer medium results from the oxidation of the reduced PMS by photooxidized reaction centers. The slow decrease of the external MP+ concentration is due to active transport of MP+ into the internal space of the chromatophores via a mechanism of a chemiosmotic type. The accumulation of MP+ is directly mediated by the redox reactions of PMS at the outer and inner surfaces of the photosynthetic membrane, which are involved in cyclic electron transport.

[Effect of iontophoretic application of acetylcholine on the discharge rate and action potential shape of pacemaker cells]. / Vliianie iontoforeticheskoi applikatsii atsetilkholina na ritm razriadov i formu potentsiala deistviia kletok peismekera.

A study was made of the action of iontophoretic application of acetylcholine to the limited number of pacemaker cells with a simultaneous recording of the activity of one of them. It was shown that both generalized and strictly localized action of acetylcholine is capable of exerting different chronotropic effects. Acceleration of the rhythm was normally accompanied by an increase in the rate of accretion of slow diastolic depolarization (SDD) and by a decrease in the action potential. The same pacemaker cell was demonstrated to modulate the direction of the chronotropic reaction for an opposite one depending on acetyl-choline concentration. Low concentration of the mediator induced rhythm acceleration and an increase in the accretion rate of SDD whereas high concentration led to rhythm deceleration and SDD lowering.

[Energy-dependent uptake of phenazinemethosulfate in isolated chloroplasts]. / Energozavisimoe pogloshchenie fenazinmetosul'fata v izolirovannykh khloroplastakh.

The concentration and absorption of methylphenazinium cations (MP+) in suspensions of pea chloroplasts are simultaneously lowered during rapid (approximately 10s) illumination. The light-induced changes of absorption and concentration of MP+ reveal similar sensitivity towards some inhibitors and uncouplers and are determined by MP+ uptake by the thylakoids. The time-course of light-induced MP+ uptake was found to be modified in the presence of dithioerythritol, Mg2+ and ATP, i. e. under conditions which induce the ATPase activity and ATP hydrolysis in chloroplasts. The kinetic curve of light-induced MP+ uptake under these conditions consists of a relatively fast (approximatley 10 s) and a slow (approximately 10 min) components. The slow ATP-dependent component of MP+ uptake is enhanced by low concentrations of gramicidin and is completely inhibited by the energy transfer inhibitor--dicyclohexylcarbodiimide. The data obtained suggest that the light-induced energization of the chloroplast membrane is accompanied by the transport of MP+ into the thylakoids against the electrical potential and concentration gradients.

[Photo-induced H+ transport in Nitellopsis obtusa cells]. / Fotoindutsirovannyi transport H+ v kletkakh Nitellopsis obtusa.

Light-induced changes of pH in the vacuole as well as changes of the electric potential difference across the plasmalemma and the tonoplast of Nitellopsis obtusa were measured simultaneously by means of conventional and H+-specific glass or antimony microelectrodes. Illumination is found to produce a decrease in pH of the vacuolar sap by 0.1-0.5 units concomitant with cell depolarization. Cells suspended in a medium with pH 9.0 exhibit great (up to 100 mV) light-induced potential changes but only small pH changes of the vacuolar sap. When pH of the external medium (pH0 in shifted from 9.0 to more acid values the amplitude of photoinduced changes of pH in the vacuole rises up to 0,3-0.5 pH units and the amplitude of the potential changes at the plasmalemma gets smaller. At pH0 = 9.0 a transient acidification of the medium is observed upon illumination whereas at lower pH light-induced alkalinization was only seen. Transition of the cells from pH0 9.0 to pH0 7,5 results in cell hyperpolarization by 60-80 mv and a decrease of vacuolar pH by 0.4-0.5 units under light conditions but has no significant effect on the potential and the vacuolar pH in the darkness. It is proposed that mechanisms of active H+ extrusion from the cytoplasm are located both at the plasmalemma and tonoplast. Light-induced depolarization seems to be determined by the increase of H+-conductance of the plasmalemma and by a correspondent decrease in the electrogenic components of the membrane potential. The ratio of light-induced H+-fluxes across the tonoplast and the plasmalemma depends crucially on the level of H+-conductance of the plasmalemma.

Photoinduction kinetics of electrical potential in a single chloroplast as studied with micro-electrode technique.

1. Using single chloroplasts of Peperomia metallica the kinetics of light-induced potential changes were studied. Three kinetic components (the initial fast rise, the decay in the light and the decay in the dark) were found to be characterized by time constants 4, 220 and 60 ms, respectively at light intensity 5000 1x and temperature 18 degrees C. After flash excitation the potential kept on rising for about 10 ms. Cooling of the medium down to 5 degrees C had no effect on the duration of potential rise after the flash. 2. Variations in the medium temperature in the range 2-23 degrees C had little effect on photoresponse magnitude but resulted in significant acceleration of decay in the light. 3. Addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (5-)0(-6) M) resulted in suppression of the magnitude of the photoresponse but was not accompanied by any change in the rate of initial rise of potential. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea-inhibited photoresponse could be restored and even enhanced by subsequent addition of N-methylphenazonium methosulfate (10(-4) M). N-Methylphenazonium methosulfate essentially influenced the time course and light-intensity curves of photoresponse. 4. The chloroplast photoresponses were of different time-courses when elicited by red (640 nm) or far red (712 nm) light. This fact as well as an enhancement effect of combined illumination by two intermittent light beams indicate on the interaction of two photosynthetic pigment systems when the photoelectric response was formed. 5. An imposed electrical field resulted in stimulation or suppression of chloroplast photoresponse depending on the polarity of the field. No indications for the existance of "reversal potential" for photoelectric response were obtained. 6. A kinetic scheme of photoresponse formation is proposed, which includes two sequential photochemical reactions of photosynthesis.