Bioelectric control of ciliary activity

Intermittent swimming in live sea urchin sperm

Sperm of the sea urchin Tripneustes gratilla repeatedly start and stop swimming when suspended in seawater and observed by dark-field microscopy. While in the quiescent state, which usually lasts about a second, the sperm assume s shape resembling a cane, with a sharp bend of approximately 3.4 rad in the proximal region of the flagellum and very little curvature in the rest of the flagellum except for a slight curve near the tip. The occurrence of quiescence requires the presence of at least 2 mM Ca2+ in the seawater, and the percentage of sperm quiescent at any one time increases substantially when the sperm are illuminated with blue light. With intense illumination, close to 100% of the sperm become quiescent, and this percentage decreases gradually to approximately 0.3% over a 10(4)-fold decrease in light intensity. An increased concentration of K+ in the seawater also increases the percentage of quiescence, with a majority of the sperm being quiescent in seawater containing 80 mM KCl. The induction of quiescence by light or by increased KCl is completely inhibited by 10 micrometers chlorpromazine, and approximately 90% inhibited by 1 mM procaine or sodium barbital. Sperm treated with the divalent-cation ionophore A23187 swim quite normally, although for a relatively short period, in artificial seawater lacking divalent cations, but are abruptly arrested upon addition of 0.04--0.2 mM free Ca2%. The flagellar waveform of these arrested sperm is almost identical to that of light-induced quiescence in the live sperm. The results support the hypothesis that quiescence is induced by a rise in intracellular Ca2%, perhaps as a consequence of a membrane depolarization, and that it is similar to the arrest response in cilia.

Hydrostatic pressure reversibly blocks membrane control of ciliary motility in Paramecium

A hydrostatic pressure of only 68 atmospheres prevented swimming Paramecium caudatum from "avoiding" or reversing direction; 170 atmospheres stopped or decreased forward velocity by more than 75 percent. A decompression of 40 atmospheres invoked a single reversal, even at ,80 atmospheres. In contrast, 170 atmospheres did not significantly affect swimming behavior of paramecium "models" that were reactivated in a solution containing adenosine triphosphate and magnesium ions after their membrane had been disrupted by Triton X-100.

Physiological dissection of various effects of ruthenium red dye on Paramecium cells

Polycationic dye ruthenium red, but not alcian blue, if externally applied to Paramecium cells quickly inhibits their phagocytosis. Ruthenium red combined with the cell surface diminishes frequency and duration of ciliary reversals and gradually inactivates the Ca++ gating mechanism. This effect persists for 1-3 after ruthenium red removal from the culture medium.

Axenic Paramecium caudatum. I. Mass culture and structure

To establish and grow Paramecium caudatum in mass axenic culture the culture medium of Soldo, Godoy & van Wagtendonk was modified by substituting phosphatidylethanolamine (PE) for TEM-4T and by a 10-fold increase in folic acid. Population densities of 4000 to 6000 cells/ml and a generation time of 20-26 h are regularly obtained. Optimal growth is obtained with PE-stigmasterol ratios between 40:1 to 400:1. Cells from 1-day-old axenic cultures have many lipid bodies aggregated in clumps (which disappear in 2 to 3 days) as well as foci of rough endoplasmic reticulum bordered by dictyosomes. The latter suggests a very active metabolism. Crystalline sheets found in both food vacuoles and lysosomes presumably play a role in digestion. Axenically grown cells also have abundant Golgi bodies (dictyosomes) and by late log phase become filled with lysosomes.

Membrane potential changes during chemokinesis in Paramecium

Intracellular recordings show that (i) paramecia hyperpolarize slightly in attractants and depolarize in repellents that depend on the avoiding reaction (an abrupt change of swimming direction), and (ii) paramecia more strongly hyperpolarize in repellents and more strongly depolarize in attractants that depend on changes of swimming velocity. These membrane potential changes are in agreement with a hypothesis of membrane potential control of chemokinesis in Paramecium.

Biochemical studies of the excitable membrane of Paramecium tetraurelia. II. Phospholipids of ciliary and other membranes

The phospholipids of cilia and deciliated bodies of Paramecium tetraurelia were isolated and characterized. 1-alkyl-2-acyl-sn-glycero-3-(2'-aminoethyl) phosphonate (GAEPL), phosphatidylethanolamine, and 1-alkyl-2-acyl-sn-glycero-3-phosphorylcholine (GPC) were the major lipids of Paramecium, and the minor lipids included phosphatidylinositol, cardiolipin, ceramide-(2-aminoethyl) phosphonate (CAEP), ceramide phosphorylethanolamine (COPE) and four sphingolipids whose identity was not established. The deciliated bodies contained 4% cardiolipin, 15% GAEPL, 41% phosphatidylethanolamine, 30% GPC and 3% each of CAEP and phosphatidylinositol; the cilia contained no cardiolipin, 24% GAEPL, 37% phosphatidylethanolamine, 15% GPC, 15% CAEP, 3% phosphatidylinositol, 2% COPE and small amounts (approx. 1%) of the four uncharacterized sphingolipids. No alteration in phospholipid composition was found among cells harvested in the various stages of growth. The phospholipids of six Paramecium mutants of three distinct phenotypes (pawn, paranoiac and fast) were also examined. Only one significant difference was found on comparison of the whole cell, deciliated body and cilia fraction of the mutants with the analogous fractions from wild type cells: the fast mutant, fA 97, had two extra, minor phospholipids (approx. 2%) in the deciliated body fraction that were tentatively identified as 1,2-diacyl-sn-glycero-3-(2'-aminoethyl) phosphonate (AEPL) and 1-alkyl-2-acyl-sn-glycero-3-phosphorylethanolamine (GPE).

Control of ciliary activity in paramecium--IV. Ca2+ modification of Mg2+ dependent dynein ATPase activity

1. Dynein proteins were solubilized from demembranated cilia of Paramecium by extraction at high ionic strength. 2. Mg2+-dependent ATPase (EC 3.6.1.3) activity of crude dynein extracts was inhibited by micromolar concentrations of Ca2+ ions. 3. Sepharose 4B chromatography of the crude extracts yields three dynein fractions. The major fraction contains a single protein and is insensitive to Ca2+ ions. Two other fractions, both heterogeneous in composition, show opposing Ca2+ ion sensitivity expressed as a Ca2+ dependent alteration in MgATP2- dependent ATPase activity. The Ca2+ ion sensitive forms show altered electrophoretic mobility on native polyacrylamide gels in the presence and absence of Ca2+ ions. 4. The data provides evidence for a Ca2+ ion dependent concomitant alteration in both molecular form and hydrolytic activity of the dyneins. The results are discussed in terms of a possible molecular mechanism for Ca ion regulation of ciliary activity in terms of the sliding microtubule model.

Calcium entry leads to inactivation of calcium channel in Paramecium

Under depolarizing voltage clamp of Paramecium an inward calcium current developed and subsequently relaxed within 10 milliseconds. The relaxation was substantially slowed when most of the extracellular calcium was replaced by either strontium or barium. Evidence is presented that the relaxation is not accounted for by a drop in electromotive force acting on calcium, or by activation of a delayed potassium current. Relaxation of the current must, therefore, result from an inactivation of the calcium channel. This inactivation persisted after a pulse, as manifested by a reduced calcium current during subsequent depolarization. Inactivation was retarded by procedures that reduce net entry of calcium, and was independent of membrane potential. The calcium channel undergoes inactivation as a consequence of calcium entry during depolarization. In this respect, inactivation of the calcium channel departs qualitatively from the behavior described in the Hodgkin-Huxley model of the sodium channel.

A potassium conductance activated by hyperpolarization in paramecium

Voltage clamp studies show that the wild-type membrane of Paramecium tetraurelia contains a conductance component which is sensitive to hyperpolarization. This component manifests itself as "anomalous", or "inward going", rectification of membrane voltage in response to applied constant current pulses and as a "hyperpolarizing spike" when no K is added to the external solution (Y. Satow, C. Kung, 1977. J. Comp. Physiol. 119:99). Like the conductances which underlie anomalous rectification in other cells, the hyperpolarization-sensitive conductance in Paramecium is specific for K, and the magnitude of the voltage-dependent conductance change depends not only on voltage but also on external potassium concentration. The internal potassium ion concentration of Paramecium is calculated to be between 17 and 18mM.

Localization of calcium channels in Paramecium caudatum

1. Electrical recordings from Paramecium caudatum were made after removal of the cilia with chloral hydrate and during ciliary regrowth to study the electrical properties of that portion of the surface membrane enclosing the ciliary axoneme. 2. Removal of the somatic cilia (a 50% reduction in membrane surface area) results in an almost complete elimination of the regenerative Ca response, all-or-none Ba2+ spike, and delayed rectification. 3. A twofold increase in input resistance resulted from the 50% reduction in membrane surface area. 4. The electrical properties remained unchanged, despite prolonged exposure to the chloral hydrate, until the cilia were mechanically removed. 5. Restoration of the Ca response accompanied ciliary regrowth, so that complete excitability returns when the cilia regain their original lengths. 6. It is concluded that the voltage-sensitive Ca channels are localized to that portion of surface membrane surrounding the cilia. 7. Measurements of membrane constants before and after deciliation and estimations of the cable constants of a single cilium suggest that the cilia of Paramecium may be fully isopotential along their length and with the major cell compartment.

Influence of electric fields on photophobic reactions in blue-green algae

The effect of external electric fields on photo-accumulations of Phormidium uncinatum in light traps has been studied. 1. In direct current fields the phobic reaction of trichoms leaving the light field is not impaired if a voltage of 2.5 V is not exceeded. With voltages between 3 and 7 V the trichoms are motile, but phobic reactions are cancelled, provided the organisms are oriented more or less parallel to the electric field lines. Higher voltages cause the algae to die within minutes. 2. Only alternating current fields of very low frequencies (less than or equal 10(-3) Hz) have similar effects. Sine waves are more effective than triangular ones, but less than square waves. A hypothesis is proposed according to which sensory transduction of photophobic reactions in blue-green algae is mediated by changes in the endogenous membrane potential. This potential might be interfered with by the application of an external electric field, thus inhibiting photophobic reactions.

Separation of membrane currents using a Paramecium mutant

The net membrane current of the electrically excitable membrane of Paramecium during step depolarisations was measured using voltage-clamp techniques. The mutant, pawn B, lacks a functional Ca channel. Thus the difference between the total current measured in the wild type and the leakage and rectification currents measured in the pawn mutant is the Ca current. These findings were confirmed by ion substitution experiments. The possibility that inactivation may be apparent only, and caused by a hypothetical, superposed, Ca-induced, rectifying K+ current was eliminated.

What does Halobacterium tell us about photoreception?

A photosensory mechanism is proposed for Halobacterium halobium based on the observation of light-induced motor responses. Possible mechanisms of signal transduction in Halobacterium are discussed. Bacteriorhodopsin and the visual pigment rhodopsin are compared with respect to their structural and functional properties. The conclusion is drawn that Halobacterium may help to understand primary photochemical events of rhodopsin rather than the transduction mechanism of visual photoreceptors.

Fine structural localization of phosphatases in cilia and basal bodies of Tetrahymena pyriformis

Cytochemical localization of ATPase activities in cilia and basal bodies of Tetrahymena pyriformis revealed a number of possible sites of ATPases. In basal bodies, reaction product was localized on the periphery of basal body microtubules, in the core of the B-microtubules, on the dense basal body core, and on the basal plate; some reaction product was associated with the postciliary and basal microtubules. In the cilium, reaction product was associated with the ciliary membrane, the basal granule, the periphery of the outer doublet microtubules, in the core of the B-microtubules, and on the arms and either the central microtubules or the radial spoke heads. Reaction product deposition required ATP and either Ca2+ or Mg2+ or ADP and Mg2+. When incubated in the presence of ATP and Na+, reaction product was only found at the base of the cilium in the region of the ciliary necklace. Implications of the various sites of activity are discussed with respect to possible mechanisms of ciliary motility.

Change in membrane potential during bacterial chemotaxis

To find out if there are changes in membrane potential during bacterial chemotaxis, we measured the membrane potential of Escherichia coli indirectly by use of the permeating, lipid-soluble cation triphenylmethylphosphonium. Addition of attractants or repellents to the bacteria brought about a hyperpolarizing peak (as well as additional, later changes in membrane potential). This peak was shown to be a part of the chemotactic mechanism based on the following evidence: (i) All attractants and repellents tested gave this peak while chemotactically inert chemicals did not. (ii) Mutants lacking galactose taxis failed to give the peak with galactose but did with another attractant and with repellents. (iii) Methionine, required for chemotaxis, is also required for production of this peak. (iv) A mutant in a control gene )flaI), unable to synthesize flagella and cytoplasmic membrane proteins related to motility and chemotaxis, failed to give the peak. (v) Paralyzed (mot) mutants gave little or none of the peak. Generally nonchemotactic (che) mutants, on the other hand, did give this peak. Very likely there are ion fluxes that bring about this change in membrane potential. We discuss the possible role of the mot gene product as an ion gate controlled by a methylation-demethylation process in response to attractants and repellents acting through their chemoreceptors.

Biochemical studies of the excitable membrane of Paramecium aurelia. I. 45Ca2+ fluxes across resting and excited membrane

The characteristics of Ca2+ transport across the excitable membrane of Paramecium aurelia were studied by measuring 45Ca2+ influx and efflux. The intracellular concentration of free Ca2+ in resting P. aurelia was at least ten times less than the extracellular concentration. Ca2+ influx was easily measurable at 0 degrees C, but not at 23 degrees C. The influx of 45Ca2+ was stimulated by the same conditions which cause membrane depolarization and ciliary reversal. Addition of Na+ and K+ (which stimulate ciliary reversal) resulted in a 10-fold increase in the rate of Ca2+ influx. An externally applied, pulsed, electric field (1-2 mA/cm2 of electrode surface), caused the rate of Ca2+ influx to increase 3-5 times, with the extent of stimulation dependent on the current density and the pulse width. Ca2+ influx had the characteristics of a passive transport system and was associated with the chemically or electrically triggered Ca2+ "gating" mechanism, which has been studied electrophysiologically. In contrast, Ca2+ efflux appeared to be catalyzed by an active transport system. With cells previously loaded at 0 degrees C with 45Ca2+, Ca2+ efflux was rapid at 23 degrees C, but did not occur at 0 degrees C. This active Ca2+ efflux mechanism is probably responsible for maintaining the low internal Ca2+ levels in unstimulated cells.