Takao Sibaoka

Excitable Cells in Mimosa

By inserting microelectrodes into cells of various tissues, it was shown that elongated parenchyma cells in the phloem and protoxylem, which have larger membrane potential than inexcitable cells of other types, generate action potentials with conduction. The electrical features of these cells are essentially similar to those of nerve and muscle cells.

Coupling between action potential and bioluminescence inNoctiluca: Effects of inorganic ions and pH in vacuolar sap

Summary1.The ionic dependency of the flash-triggering action potential (FTP) evoked across the vacuolar membrane inNoctiluca was studied by injecting various salt and pH buffer solutions into the vacuole.2.Electron microscopic observations showed that the peripheral cytoplasmic compartment sandwiched between vacuole and pellicle is 0.11±0.07 μm in thickness, so that it has a very small volume (Figs. 2 and 15).3.The resting membrane resistance and capacitance measured across the cell surface were about 10 KΩ·cm2 and 0.8 μF/cm2, respectively. Under normal conditions the FTP, which is 50∼60 mV in amplitude, arises from a potential of −150 to −160 mV.4.More than a tenfold increase in the concentration of K+, Ca2+, Mg2+, NH4+, or SO42− in the vacuole produced no significant change in the amplitude of FTP (Figs. 4 and 5).5.Injections of HCl-glycine buffer solutions of various pH were used to alter the intrinsic vacuolar pH (about 3.5) within the range of 2.5 to 3.7 without damaging the cells. The FTP amplitude rose about 58 mV per unit drop in pH (Figs. 6–9, Table 1).6.Crude aqueous extracts from the cells emitted light most effectively when the pH was lowered from 8.2 to 5.5. None of the other major cations found in the vacuole showed any effect on the light emission of the extract (Figs. 12 and 13).7.From these findings, we propose a proton hypothesis explaining the coupling between the bioluminescence and the action potential.

Water Extrusion in the Trap Bladders of Utricularia vulgaris-1-A Possible Pathway of Water across the Bladder Wall

In the trap bladder ofUtricularia vulgaris, a sudden expansion (convex bladder) by opening of the entrance door upon stimulus was followed by slow decreases in bladder width and internal hydrostatic pressure. The decreases were caused by continuous water outflow from bladder lumen. The bladder reached initial resetting state (concave bladder) in about 30 min. The internal pressure reduced to 0.86 bar. This reduction was inhibited by application of sodium azide in the bladder lumen. The total water outflow for 30 min from a bladder, measured using a glass capillary inserted in the bladder, was 630 nl: the rate was 21 nl/min. This rate was also inhibited by sodium azide. In bladder resetting under paraffin oil, it was observed that water emerges from near the free edge of the trap door. From light and electron microscopic observations of the entrance region, it is concluded that the inlet of water outflow is the bifid trichomes which stand on the inner surface of the bladder near the entrance, and the outlet is the outer and middle zones of the pavement epithelium, or threshold, against which the free edge of the door rests.

Water extrustion in the trap bladders ofUtricularia vulgaris

In the trap bladder ofUtricularia vulgaris, increase in sucrose concentrations in bladder lumen fluid decreased resetting rate. Addition of 350 mM sucrose to lumen fluid stopped the resetting. Therefore, water seems to move down the water potential gradient between the lumen and the arm cells of bifid trichomes, which are the site of inlet in the water pathway. Application of dinitrophenol, sodium azide, KCN, monoiodoacetic acid or pentachlorophenol in lumen fluid much reduced the water outflow. Temperature coefficient of bladder resettings was about 2. No effect of darkness on resetting rate was found. These facts show that the resetting requires energy supplied from respiration and there exists an active ion transport mechanism somewhere in the water pathway. No effect on the resetting was seen upon immersing the bladder in 700 mM surcose solution. In the capital cells of the pavement epithelium in its outer and middle zones, which are the site of outlet in water pathway, membrance potential and resistance were lower than those in other cells. These facts indicate that bulk flow of the cell sap from the capital cells to the outside takes place by intracellular hydrostatic pressure.

Tentacle regulating potentials inNoctiluca miliaris: their generation sites and ionic mechanisms

SummaryMembrane potential responses that regulate movement of the food-gathering tentacle ofNoctiluca miliaris (tentacle regulating potentials, TRPs) were examined electrophysiologically under various ionic conditions. These spontaneous TRPs were modified by changing the external ionic conditions. Positive spike appeared as external Ca2+ concentration was lowered. The peak of the spike became more positive with increasing external Na+ concentration. The spike could be evoked by injecting a depolarizing current when the membrane was hyperpolarized. The positive spike is assumed to be caused by regenerative activation of depolarization-sensitive Na channels. The peak of the negative spike, reported by previous workers, became more negative with increasing external Cl− concentration. The spike was evoked by injecting a hyperpolarizing current when the membrane was depolarized. The negative spike is assumed to be caused by regenerative activation of hyperpolarization-sensitive Cl− channels. The waveforms and amplitudes of the TRPs recorded from the nucleus were identical to those recorded from the flotation vacuole. This suggests that the TRPs are generated on the membrane facing the external solution. Possible roles of the TRPs in the control of tentacle movement are discussed.

Transmission of action potentials inBiophytum

By cooling or by electrical stimulus an action potential, (60 to 100 mv negative) was propagated throughout the length of a pinna-rachis or a peduncle ofBiophytum sp. A cutting stimulus evoked a series of two to four transmission of actions of action potentials. The transmission did not pass through the base of the leaf or peduncle. The velocity of the transmission in the rachis and penduncle was about 0.2 cm/sec, and no difference in the velocity was found between the acropetal and basipetal directions. In the stimulated site a local response (a negative bulge of potential) was seen with threshold stimulus. The absolute refractory period for the transmission of action potential was estimated at 20 to 50 sec, and the relative one at 30 to 70 sec. The mechanism of the transmission seemed to be similar to that inMimosa pudica.

Application of leaf extract causes repetitive action potentials inBiophytum sensitivum

A wound stimulus evoked a number of repetivite action potentials in the leaf ofBiophytum sensitivum. When the cut end of a leaf was immersed in a leaf extract, the resulting repetitive action potentials continue for a long time. These repetitive action potentials disappeared immediately when the leaf extract, which contains a proposed stimulant, was removed and the cut end was washed with water.