A [Na+]o-independent, pHo-dependent mechanism for reduction of intracellular [Ca2+] after influx through Ca2+ channels in mouse pituitary cells

The effect of extracellular pH (pHo) on the duration of calcium-dependent chloride currents (ICl(Ca] was studied in voltage clamped AtT-20 pituitary cells. ICl(Ca) was activated by Ca2+ influx through plasma membrane Ca2+ channels, which were opened by step depolarization to voltages between -20 and +60 mV. Increasing pHo from 7.3 to 8.0 reversibly prolonged ICl(Ca) tail currents in perforated patch recordings from cells bathed in both Na(+)-containing and Na(+)-free solutions. This prolongation was prevented in standard whole cell recordings when the pipette solution contained 0.5 mM EGTA. The effects of raised pHo were not due to alteration of intracellular pH, since tail current prolongation still occurred when intracellular pH was buffered at 7.3 with 80 mM HEPES. The prolongation of ICl(Ca) at pHo 8 could not be accounted for by a direct action on Ca2+ channels, since tail currents were prolonged when pHo was changed rapidly during the tail current, after all Ca2+ channels were closed. The effects of increasing pHo on ICl(Ca) also could not be explained by a direct action on Cl- channels, since changing to pHo 8 did not prolong Cl- tail currents when intracellular Ca2+ concentration [( Ca2+]i) was fixed by EGTA in whole cell recordings. Raising pHo did, however, prolong depolarization-evoked [Ca2+]i transients, measured directly with the Ca2+ indicator dye, fura-2. Taken together, these data demonstrate the presence of a Na(+)-independent, pHo-sensitive mechanism for reduction of [Ca2+]i after influx through Ca2+ channels. This mechanism is associated with the plasma membrane, and is active on a time scale that is relevant to the duration of single action potentials in these cells. We suggest that this mechanism is the plasma membrane Ca2+ ATPase.     

The influence of biomass and structure of the crustacean plankton on the water transparency in the Saidenbach storage reservoir

Planktonic crustacean biomass as well as structure are important factors influencing water transparency. The significant dependence of the water quality (Secchi depth) on the concentration and the share of the Daphnia biovolume and not on the total Crustacea biovolume in the Saidenbach reservoir indicates that the density of the Crustacea is only a measure of the cleaning performance, if Daphnia dominates. Using the mean size, the influence of the crustacean structure on the Secchi depth can be recorded. If big size categories prevail (like Daphnia) the water transparency is high. The mainly occurrence of little species (Mesocyclops, Bosmina) results in lower Secchi depths. However, a well defined (significant) relationship is being prevented by the different feeding behaviour of the several species.     

Biochemical and physiological characterization of the efrotomycin fermentation

Summary An efrotomycin fermentation was characterized through physical, chemical and biochemical studies. Growth of the actinomycete,Nocardia lactamdurans occurred during the first 50 h of the fermentation cycle at the expense of glucose, protein, and triglycerides. The initiation of efrotomycin biosynthesis was observed when glucose dropped to a low concentration. Upon glucose depletion, cell growth ceased and a switch in the respiratory quotient occurred. Efrotomycin biosynthesis was supported by the utilization of soybean oil and starch. Analysis of triglyceride metabolism showed that no diglycerides or monoglycerides accumulated during the fermentation. The activity of extracellular enzymes (lipase, protease, and amylase) increase during the cell growth phase and decreased significantly after 150 h. The concentrations of DNA, tetrahydro-vitamin K₂ (a membrane component), and free amino acids in the supernatant increased dramatically late in the fermentation cycle (225 h), indicating massive cell lysis. During this same time period, a reduction in cellular respiratory activity and efrotomycin biosynthesis were observed.     

Photoautotrophic growth of soybean cells in suspension culture. II. Optimization of culture medium and conditions

We have attempted to optimize the conditions under which a photoautotrophic soybean suspension culture line (SB-P; Horn et al. 1983) is grown. Magnesium, phosphate, and calcium concentrations were varied individually from one-tenth to five times the normal level found in the Murashige and Skoog (1962) recipe. After two subcultures, only phosphate at one-tenth the normal level caused the cells to show a substantial reduction in fresh and dry weight increase and chlorophyll level. Nitrate and ammonium levels were inversely varied in 20 millimolar increments of potassium nitrate and ammonium chloride. Neither N-source alone could support growth through two subcultures. A ratio of 40 millimolar potassium nitrate to 20 millimolar ammonium gave significantly better fresh and dry weight increases than did a ratio of 20:40 or 30:30 but the chlorophyll level was unchanged. The minor salts as a group resulted in a small improvement in growth when provided at twice the normal level.Indole-3-acetic acid at five milligrams per liter resulted in significantly better fresh and dry weight increases than did -naphthaleneacetic acid at any level but the final chlorophyll level was not changed. There was no correlation between growth and kinetin level and this resulted in the discovery that SB-P cells are cytokinin-autotrophic, as are heterotrophic SB cells, with regard to both growth and greening ability. Growing SB-P cells under a 14 h:10 h day:night photoperiod resulted in a slow but inevitable death. Increasing the carbon dioxide level to 10% for four weeks gave no increase in SB-P cell growth or chlorophyll level, but SB-P cells would not grow with carbon dioxide levels below 0.4%. The results clearly show that SB-P cells, despite their tenuous existence, are capable of adapting to a wide range of culture conditions. A simplified and improved culture medium for photoautotrophic cultures is given.Abbreviations SB-P photoautotrophic soybean cells - SB-M photomixotrophic soybean cells - SB-H heterotrophic soybean cells     

Estimating the number of channels in patch recordings

The estimation of the number of channels in a patch was assumed to be equivalent to the estimation of the binomial parameter n. Seven estimators were evaluated, using data sets simulated for a range of parameters appropriate for single channel recording experiments. No single estimator was best for all parameters; a combination of estimators is a possible option to avoid the biases of individual estimators. All estimators were highly accurate in estimating n in the case that n = 1. For n ≤ 4 the simplest estimator, the maximum number of simultaneously open channels, was the best, For larger values of n the best estimators were Bayesian.     

Culture conditions for induction of green plants from barley microspores by anther culture methods

Summary With barley a large variation in frequency of plant formation from microspores of spikes from the same plant has been observed. The highest frequency of plant formation was obtained when culturing anthers in the dark on a high Ficoll medium containing 2,4-D and kinetin to induce proembryo (or callus) formation. Subsequently the proembryos or calli were cultured in dim light on a high Ficoll-high sugar medium containing IBA and kinetin. Finally the embryos were transferred to a starch agar medium. A maximum of 13 green plants were obtained from microspores of a single anther.The ratios of green to albino microspore derived plants varied from 91 to 19 depending on culture conditions. Under anaerobic conditions, lactic acid and other organic acids may have damaged the organelles in the cells resulting in the formation of albino plants. Thus, direct embryogenesis by using a well-buffered, high Ficoll-high sugar medium and proper aeration are essential for obtaining high frequency of green plants from microspores.Abbreviations 2,4-D 2,4 dichlorophenoxyacetic acid - IBA 3 indolylbutyric acid