Taste responses of the gerbil IXth nerve

Summated taste responses to 12 taste solutions were recordedfrom the IXth (glossopharyngeal) nerve of 38 Mongolian gerbils(Meriones unguiculatus). 0.3 M NH₄Cl was the most effectivestimulant. The relative magnitude of the peak summated responsewas a positively accelerated function of log molar concentration.Absolute thresholds were determined for three chemicals: 0.002M NaCl, 0.0003 M HCl, and 0.002 M sucrose. The relative magnitudesof the responses to quinine, NH₄Cl, and KCl were greater forthe IXth nerve than for the chorda tympani nerve, whereas NaClwas more effective for the chorda tympani. A similar patternis seen in the rat. Acetic and citric acid may bind to commonreceptor sites. NH₄Cl, KCl, and HCl may also have receptor sitesin common.     

The neural activities of the greater superficial petrosal nerve of the rat in response to chemical stimulation of the palate

A comparison of the integrated responses of the rat's greatersuperficial petrosal (GSP) and chorda tympani (CT) nerves toa number of taste stimuli was studied. The GSP nerve of therat was very responsive to the chemical stimulation of the oralcavity. Among the selected stimuli related to the four basictaste qualities, 0.5 M sucrose produced the greatest neuralresponse in the GSP nerve, whereas, 0.1 M NaCl produced thegreatest in the CT nerve. The GSP nerve integrated responseto 0.5 M sucrose solution was approximately three times as greatin magnitude as that to a 0.1 M NaCl solution. The neural responsemagnitude of the GSP and CT nerves were as follows: GSP nerve;0.5 M sucrose >0.02 M Na-saccharin >0.05 M citric acid>0.1 M NaCl > 0.01 M quinine-HCl. CT nerve; 0.1 M NaCl> 0.05 M citric acid > 0.02 M Na-saccharin > 0.01 Mquinine-HCl >0.5 M sucrose. The response magnitudes of theGSP nerve to 0.3 M chloride salt solutions were: LiCl > CaCl₂> NaCl > NH₄Cl > KCl, whereas the response magnitudesof the CT nerve to the above salts were: LiCl > NaCl >NH₄Cl > CaCl₂ > KCl. All 0.5 M solutions of the selectedsugars (sucrose, rhamnose, galactose, lactose, fructose, -methyl-D-glucoside,xylose, mannose, arabinose, maltose, sorbose and glucose) evokedneural responses in both GSP and CT nerves. The order of theresponse magnitudes of the GSP nerve to the selected sugarswas similar to that of the CT nerve but the absolute magnitudesof the GSP nerve were greater.     

Inhibition of hamster chorda tympani neural response by copper chloride

Copper chloride was evaluated as a specific inhibitor of neuralresponses to sweet taste stimuli in the goldern hamster (Mesocricetusauratus). The chorda tympani whole-nerve response to taste stimuliwas recorded before and after the tongue was treated for 30s with 0.01, 0.1 and 1 mM CuCl₂. Sweet stimuli [sucrose, fructose,saccharin (calcium salt), D-phenylalanine], which primarilystimulate chorda tympani S fibers, and non-sweet stimuli (NaCl,NH₄Cl) were used. At 0.01 mM, copper chloride had little effect.At 0.10 mM it partially inhibited responses to sucrose and saccharin,but had little effect on responses to D-Phe, fructose, NaCl,NH₄Cl, or a mixture of sucrose plus L-Phe. L-Phe, which hasthe same chelating properties as D-Phe, is not an S-fiber stimulusand likely reduced sucrose inhibiton by chelating the cupricion.Analysis of concentration–response functions revealedthat 0.1 mM copper chloride inhibited the neural response tolow concentrations of sucrose by about 25%, but did not significantlyinhibit high concentrations of surcrose, suggesting competitiveinhibition. In contrast, 0.1 mM CuCl₂ reduced saccharin responsesby 25% throughtout the effective range, suggesting non-competitiveinhibition. Occupation of a saccharide receptor site by coppermay interfere with dimer but not monomer reception and distortthe saccharin receptor site. At 1 mM, CuCl₂ non-competitivelyinhibited responses to sucrose, fructose, saccharin and thenon-sweet NaCl (an N-fiber stimulus), but not NH₄Cl (an H-fiberstimulus). The mechanisms of copper chloride inhibition aredifficult to establish because its effects are weak at concentrationswhere they are specific.     

Neural responses and aversion to bitter stimuli in rats

Gustatory responses of rats to quinine, nicotine, caffeine,MgCl₂ and bitter peptides such as glycyl-L-phenylalanine (Gly-Phe)and glycyl-L-isoleucine (Gly-lle), were studied by recordingintegrated responses to bitter stimuli from the chorda tympaniand IXth nerve as well as by measuring fluid intakes with atwo-bottle choice method. In addition, the effect of L-glutamyl-L-glutamicacid (Glu-Glu), which has an ability of masking bitterness inhumans, on the IXth nerve response was examined. Quinine, nicotine and caffeine elicited aversive behavior atconcentrations similar to those eliciting the IXth nerve responses,while MgCl₂ induced aversion above 0.1 M although it producedneural responses at much lower concentrations in both nerves.No aversion was produced by the bitter peptides at 30 mM, althougha small response was elicited by Gly-Phe in the chorda tympaniand by Gly-Ile in the IXth nerve. Responses in the IXth nerveto mixtures of Glu-Glu with bitter substances was smaller thanthe sum of those for single solution alone, indicating depressionof nerve responses to bitter stimuli by Glu-Glu.     

Chemical and structural changes of neurofilaments in transected rat sciatic nerve

The sequence of changes occurring in transected rat sciatic nerve was examined by electron microscopy and by sodium dodecyl sulfate (SDS) polyacrylamide disc gel electrophoresis. Representative segments of transected nerves were processed for ultrastructural examinations between 0 and 34 days after the transection of sciatic nerves immediately below the sacro-sciatic notch. The remainder of the transected nerves and the intact portions of sciatic nerves were desheathed and immediately homogenized in 1 percent SDS containing 8 M urea and 50 mM dithioerythritol. Solubilized proteins were analyzed on 12 percent gels at pH 8.3 in a discontinuous electrophoretic system. Initial changes were limited to the axons of transected nerve fibers and were characterized by the loss of microtubules and neurofilaments and their replacement by an amorphous floccular material. These changes became widespread between 24 and 48 h after transection. The disruption of neurofilaments during this interval occurred in parallel with a selective loss of 69,000, 150,000 and 200,000 mol wt proteins from nerve homogenates, thus corroborating the view that these proteins represent component subunits of mammalian neurofilaments. Furthermore, the selective changes of neurofilament proteins in transected nerves indicate their inherent lability and suggest their susceptibility to calcium-mediated alterations. Electrophoretic profiles of nerve proteins during the 4-34-day interval after nerve transection reflected the breakdown and removal of myelin, the proliferation of Schwann cells and the deposition of endoneurial collagen. A marked increase of intermediate-sized filaments within proliferating Schwann cell processes was not accompanied by the appearance of neurofilamentlike proteins in gels of nerve homogenates.     

Chemosensitive responses from the cat epiglottis

Responses were recorded from single and few-fiber preparationsof the cat superior laryngeal nerve during stimulation of theepiglottis with 0.5 M KCl, NH⁴Cl, NaCl, and LiCl; distilledwater, 0.005 M citric acid, 0.01 N HCl; and light touch. Epiglottalreceptive fields were mapped. The order of effective stimuliis KCl > HCl > NH⁴Cl > distilled water > citricacid; NaCl and LiCl are generally not effective. Since (a) similarstimuli elicit responses from the cat chorda tympani nerve duringstimulation of tongue taste buds, and (b) receptive fields ofsuperior laryngeal nerve fibers compare well with a map of epiglottaltaste buds, we conclude that the chemosensitive responses fromthe epiglottis are probably mediated by taste buds.     

Learned aversions and taste qualities in hamsters

Interralations among taste perceptions in gloden hamsters (Mesocricetusauratus) were examined using generalizaions of learned tasteaversions. If stimulus A is avoided given a taste aversion hasbeen established to stimulus B, and vice versa, A and B ‘cross-generalize’.Stimuli within five groups cross-generalized. The groups ofcompounds were (i) sweeteners (fructose, saccharin, sucrose);(ii) sodium salts (NaCl, NaNO₃, Na₂SO₄): (iii) non-sodium salts(KCl, MgSO₄ NH₄Cl) plus quinine HCl; (iv) acids (acetic, hydrochloric,citric); and (v) urea. Only two pairs of stimuli from differentgroups cross-generalized (HCl—NH₄Cl. quinine HCl—urea).Neural patterns of response recorded form chorda tympam nervefibers in hamsters suggest that taste receptors on the anteriortongue distinguish among three groups of taste stimuli: sweeteners,sodium salts, and a group including non-sodium salts, acids,quinine HCl and urea. Neurons innervating other taste fieldsare likely to provide the information that hamsters use to discriminateamong the tastes of non-sodium-salt and non-sweetener stimuli.     

Asymmetrical neural cross-adaptation of hamster chorda tympani responses to sodium and chloride salts

Cross-adaptation has occurred when exposure to an adapting chemicalstimulus (A) reduces the response to a subsequent test stimulus(B). The degree of cross-adaptation between two stimuli is thoughtto reflect the overlap of their ‘neural activation processes’.We measured self- (A—A) and reciprocal crossadaptation(A—B, B—A) of the response of the hamster chordatympani nerve with lingual presentations of stimuli elicitingequal unadapted transient responses. Adapting and test stimuliwere 0.1 M NaCl, 0.1 M NaNO₃, 0.1 M NaBr, 0.4 M Na acetate (NaAc),0.09 M LiCl and 0.4 M NH₄Cl. Nearly complete and symmetricalcross-adaptation was seen for NaCl, NaNO₃ and NaBr. Those Nasalts paired with LiCl showed strong but asymmetrical cross-adaptation.Exposure to sodium completely eliminated the response to LiClbut not vice versa, suggesting that lithium and sodium are notcompletely interchangeable taste stimuli for the hamster chordatympani. Relatively little cross-adaptation between NH₄Cl andother salts suggested relatively separate neural activationprocesses. Strongly asymmetrical cross-adaptation was foundbetween NaAc and the other sodium salts. Responses to NaCl,NaNO₃ or NaBr were eliminated after adaptation to NaAc whereasthe response to NaAc during the reciprocal cross was strong.Asymmetries are discussed in reference to sensitivities of singlenerve fibers for the chorda tympani, effects of adaptation andthe concept of anion inhibition.     

Salivary ions and neural taste responses in the hamster

Saliva is a chemically complex fluid that bathes oral surfacesand may affect early events in mammalian gustation. We measuredchorda tympani responses to taste stimuli in hamsters (Mesocricetusauratus) while their tongues were adapted to either water, artificialsaliva or natural saliva. Artificial saliva on the tongue loweredneural responses to taste stimuli that were present in the artificialsaliva and to those stimuli that cross-adated with salivarycomponents. Changing from a water-adapted tongue to one soakedwith pilocarpine-stimulated saliva from donor hamsters led tosignificantly smaller responses to NaCl. Responses to sucrose,NH₄Cl and quinine were unaffected. Chemical analysis of hamstersaliva revealed ‘normal’ mammalian levels of K⁺,Ca²⁺ and Mg²⁺, but unexpectedly low levels of Na⁺ and Cl^–.     

Energy conversion and changes in physical parameters in chloroplasts and subchloroplast particles II. Energy conversion in chloroplasts and different types of subchloroplast particles

The light-induced absorbance change at 515 nm, light-inducedhydrogen ion uptake and ATP formation were compared in chloroplastsand different types of sonicated subchloroplast particles. Noparallel relationship among the activities for ATP formation,hydrogen ion uptake and the 515-nm change was observed in differenttypes of preparations. NH₄Cl inhibited ATP formation in chloroplastsbut had little effect on subchloroplast particles. In contrast,the light-induced hydrogen ion uptake was inhibited by NH₄Clin a similar manner. Tetraphenylboron (TPB), at 1 µM, inhibited ATP formationby about 30% in both chloroplasts and subchloroplast particles.In the presence of TPB, ATP formation in chloroplasts was stronglyinhibited by NHC₄Cl, but in subchloroplast particles the additionalinhibitory effect of NH₄Cl was small. A synergistic inhibitionof photophosphorylation by valinomycin plus NH₄Cl was much clearer.Although acceleration of the recovery of the 515-nm change byNH₄Cl or valinomycin was moderate, the 515-nm change virtuallydisappeared when NH₄Cl and valinomycin were added simultaneously. Although the membrane potential has a major role as the principaldriving force for ATP formation in subchloroplast particles,the simultaneous abolishment of the pH gradient and membranepotential may be required to uncouple ATP formation. ¹Present address: Fukuoka Women's University, Kasumigaoka, Fukuoka813, Japan. ²Present address: Ryukyu University, Naha, Okinawa 903, Japan. (Received February 5, 1974; )     

Gustatory sensitivities of the hamster's soft palate

The response properties of taste receptors distributed on thesoft palate of the hamster were studied by recording integratedresponses from the greater superficial petrosal (GSP) nerveStimuli were concentration series of sucrose, NaCl, HCl andquinine hydrochloride (QHCl), and several other 0.1 M saltsand 0.5 M sugars. For comparison, integrated responses wererecorded from the chorda tympani (CT) nerve in many of the sameanimals from which recordings were made from the GSP. Responsesin each preparation were scaled relative to the phasic responseto 0.1 M NaCl and were then expressed for each nerve as a proportionof the total response magnitude (TRM)—the sum of all theresponses to the four concentration series. In this way, therelative response of each nerve to all of the stimuli couldbe evaluated. There were significant differences between theGSP and CT nerves in the responses to NaCl, QHCl and sucrose.Both the phasic and tonic responses to sucrose were larger inthe GSP than in the CT, whereas the tonic responses to NaCland QHCl were smaller. The slopes of the concentration-responsefunctions for NaCl, HCl and sucrose were significantly differentbetween the two nerves. The responses to 0.1 M sodium and lithiumsalts were significantly greater in the CT than in the GSP;whereas the 0.5 M sugars elicited responses in the GSP thatwere 2–3 times greater than in the CT nerve. A comparisonof the relative responsiveness to 0.3M sucrose, 0 3 M NaCl,0.01 M QHCl, 0.01 M HCl and distilled water among the GSP, CT,glossopharyngeal (IXth) nerve and superior laryngeal nerve (SLN)indicated that the vast majority of information about sucroseand NaCl is transmitted to the brainstem by the VIIth nerve. ¹Present address: Department of Oral Physiology, Kagoshima UniversityDental School, Kagoshima 890, Japan     

The Effect of Various Nitrogen Sources upon the Production of Extracellular Polysaccharide by the Blue-Green Alga Anabaena flos-aquae A-37

Anabaena flos-aquae A-37 was grown in bacteria-free cultureon a variety of nitrogen sources. Extracellular polysaccharideproduction was found to be a part of the normal metabolic processescausing the liberation of excess carbohydrates into the surroundingmedium rather than the result of cellular lysis. Non-adaptedcells supplied with NH₄Cl produced abundant polysaccharide.However, the population did not increase. Cells adapted to NH₄Clproduced smaller quantities of polysaccharide, but the populationdid increase. Polysaccharide production per cell was similaron Mg(NO₃)₂, KNO₃, NaN0₃, NH₄NO₃, and NH₄Cl. It was concludedthat an adequately utilized nitrogen source does not affectpolysaccharide production in A. flos-aquae A-37.     

Effect of Ammonia on Dark CO2 Fixation by Anabaena Cells Treated with Methionine Sulfoximine

Dark CO₂ fixation by Anabaena cylindrica was stimulated aboutthree-fold by the addition of NH₄Cl to the cells. The ¹⁴CO₂incorporation experiments showed that ¹⁴C is most rapidly incorporatedinto aspartate and then glutamine by adding NH4CI. Glutamineaccumulated predominantly after the addition of NH₄Cl showingthat NH₄ is incorporated into glutamine by glutamine synthetase.The stimulating effect of NH4Cl on CO₂ fixation and amino acidsynthesis was suppressed by methionine sulfoximine, an inhibitorof glutamine synthetase. It was suggested that dark CO₂ fixationwas stimulated by the action of glutamine synthesis which isenhanced by ammonia. (Received February 10, 1981; Accepted April 2, 1981)     

Taste responses of human chorda tympani nerve

Records from humans of summated action potential dischargesof the chorda tympani nerve were examined. The magnitudes ofneural and psychophysical responses were well related only whenthe comparison was made within a given taste quality. The responseto a mixture of 0 02 M citric acid and 0.5 M sucrose was lessthan the sum of the separate responses to the mixture components.Citric acid failed to cross-adapt the response to sucrose, implyingthe receptor sites for sucrose are independent of citric acid.The human chorda tympani nerve shows vigorous responses to mechanicalstimulation and cooling of the tongue that are maintained aftertreatment of the tongue with a water extract of the herb Gymnemasylvestre. Gymnema extract selectively suppressed the responseto all sweeteners tested (sucrose, fructose, saccharin and cyclamate)and also suppressed by – 50% the water-after-citric-acidresponse which has a predominantly sweet taste. Gymnema suppressedby 0 – 10% the water-rinse response following NaCl. fructoseand sucrose that have a predominantly bitter-sour taste. Water-rinseresponses were present even when mechanical and thermal stimulationof the tongue were minimized. The human chorda tympani nerveappears to have positive water-rinse taste responses. Theseare solute-specific off-responses that are probably mediatedby receptor sites independent of those responsible for the on-responseto the given solute.     

Control of Glutamate Dehydrogenase from Green Tobacco Callus Mitochondria by Ca2$ and pH

Glutamate dehydrogenase (GDH) (EC 1.4.1.3 [EC] .) purified from greentobacco callus mitochondria was activated markedly by Ca^2$ inthe amination reaction. This activation was detectable evenat concentrations below 5 µM Ca^2$. Saturation curves for the three substrates of the aminationreaction showed normal Michaelis-Menten kinetics in the presenceof 1 mM of Ca^2$, but pronounced substrate inhibition occurredwithout Ca^2$. The effect of Ca^2$ was chiefly on the maximalvelocity. The saturation curve for NH₄Cl in the presence of Ca^2$ was modulatedby a change in pH. The apparent K_m value for NH₄Cl markedlydecreased whereas that for -ketoglutarate increased slightlywhen the pH was raised from 7.3 to 9.0. In contrast, the K_mfor NADH was little affected by raising the pH. The characteristicof GDH which increases its affinity for NH₄Cl when the pH israised may be compatible with the detoxification of ammonia. ¹ Present address: Mochida Pharmaceutical Co., Ltd. (Received August 24, 1981; Accepted November 28, 1981)     

Effects of Ammonia on Respiration, Adenylate Levels, Amino Acid Synthesis and CO2 Fixation in Cells of Chlorella vulgaris 11h in Darkness

The effects of NH₄Cl on respiration, adenylate and free aminoacid levels as well as dark CO₂ fixation were investigated usingnitrogen-starved Chlorella vulgaris 11h cells with or withoutaddition of methionine sulfoximine (MSX), an inhibitor of glutaminesynthetase. Upon addition of NH₄Cl (1 mM) to the cells not treatedwith MSX, respiration was stimulated and the level of ATP droppedrapidly, while the levels of ADP and AMP increased. NH₄Cl alsostimulated amino acid synthesis, especially of glutamine, andmarkedly enhanced dark CO₂ fixation. Addition of NH₄Cl to MSX-treatedcells stimulated respiration and lowered the level of ATP, butdid not enhance glutamine synthesis and only slightly stimulateddark CO₂ fixation. ⁴On leave from Institute of Medical Science, Advance R &D Co. Minami-Hashimoto, Sagamihara, Kanagawa-ken 220, Japan (Received January 28, 1984; Accepted April 19, 1984)     

Acute Effects of Total or Partial Digit Denervation on Raccoon Somatosensory Cortex

The immediate effects of total or partial denervation of single digits (0-16 hr after nerve transection) on primary somatosensory cortex were studied electrophysiologically. Comparisons of response properties and cortical somatotopy were made between intact raccoons and four groups of raccoons with transection of some or all of the nerves innervating the fourth or fifth digit. Animals with all four digital nerves cut (amputation of the digit) were most different from normal. Approximately half of the penetrations in the affected cortical region showed inhibitory responses to stimulation of adjacent skin regions. These consisted of a strong response to stimulus offset and/or a suppression of spontaneous activity during indentation. Since these responses were substantially different from those recorded several months after digit amputation, additional changes in connectivity and synaptic strength must occur with chronic denervation. These inhibitory responses were not seen in animals with one, two, or three nerves cut per digit.

In the animals with partial denervation of a digit, the greatest disruption occurred when both ventral nerves to the glabrous skin were transected. This yielded cell clusters with abnormally large receptive fields, disruptions in somatotopic organization, and a decreased occurrence of low-threshold responses. If only one nerve to glabrous skin was transected, there was less change, even if it was combined with transection of both nerves to hairy skin. These results suggest that the release of inhibitory responses in a cortical digital region by amputation is prevented by the retention of even one ventral nerve. None of the denervation conditions produced large nonresponsive areas of cortex, which would have indicated a loss of all inputs.     

Differential modulation of voltage-dependent K+ currents in colonic smooth muscle by oxidants

The effect of oxidants on voltage-dependent K⁺ currents was examined in mouse colonic smooth muscle cells. Exposure to either chloramine-T (Ch-T), an agent known to oxidize both cysteine and methionine residues, or the colon-specific oxidant monochloramine (NH₂Cl) completely suppressed the transient outward K⁺ current (I_to) while simultaneously enhancing the sustained delayed rectifier K⁺ current (I_dr). In contrast, the cysteine-specific oxidants hydrogen peroxide (H₂O₂) and 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) exhibited partial and slow suppression of I_to by inducing a shift in channel availability of -18 mV without affecting I_dr. After enhancement by NH₂Cl or Ch-T, I_dr was sensitive to 10 mM tetraethylammonium but not to other K⁺ channel blockers, suggesting that it represented activation of the resting I_dr and not a separate K⁺ conductance. Extracellular dithiothreitol (DTT) partially reversed the effect of H₂O₂ and DTNB on I_to but not the actions of NH₂Cl and Ch-T on either I_dr or I_to. Dialysis of myocytes with GSH (5 mM) or DTT (5 mM) prevented suppression of I_to by H₂O₂ and DTNB but did not alter the effects of NH₂Cl or Ch-T on either I_dr or I_to. Ch-T and NH₂Cl completely blocked I_to generated by murine K_v4.1, 4.2, and 4.3 in Xenopus oocytes, an effect not reversible by intracellular DTT. In contrast, intracellular DTT reversed the effect of H₂O₂ and DTNB on the cloned channels. These results suggest that I_to is suppressed via modification of both methionine and cysteine residues, whereas enhancement of I_dr likely results from methionine oxidation alone. colon; colitis; redox; ion channel     

Amiloride does not block taste transduction in the mudpuppy, Necturus maculosus

Activity of the glossopharyngeal nerve was recorded with bipolarsilver wire electrodes while taste stimuli were applied to thelingual surface in anesthetized mudpuppies. Taste stimuli wereinjected into a continuous stream of distilled water which wasrunning over the tongue, KCl, CaCl₂ and LiCl₂ at 0.4 M elicitedbrisk responses, as did HCl at 0.2 M and quinine at 6 x 10^–4M. Sucrose, glucose and saccharin did not elicit responses.Twenty amino acids were surveyed for their ability to evokea response at 0.04 M: 1-arginine, 1-valine, 1-phenylalanine,1-tryptophan, 1-tyrosine, 1-glutamic acid, 1-lysine and histidinealways evoked responses, whereas other amino acids either didnot evoke responses or only occasionally evoked responses. Thesupernatants from solutions of minced worms and minnows andPurina Trout Chow were effective taste stimuli. Pre-adaptingthe tongue to Ringer's solution by running a continuous streamof Ringer's solution over it eliminated responses to quinineand decreased responses to NaCl. Pre-adapting the tongue to10^–4 to 10^–3 M amiloride, a potent sodium channelblocker, did not alter the responses to NaCl, LiCl, or othertaste stimuli.     

Light-induced changes in membrane potential in Spirogyra

Spirogyra cells exhibited changes in membrane potential whenthey were exposed to light. Cells made chloroplast-free didnot show any light-induced potential change (LPC) upon illuminationwith white light and also monochromatic red (680 nm) and farred (720 nm) light. LPC was observed when the cell containedonly a small fragment of chloroplast, whether the cell had anucleus or not. The magnitude of LPC depended on the amountof chloroplast in the cell. DCMU at 10^–5 M, CCCP at 10^–5 M and DNP at 10^–4M at pH 5.5 suppressed LPC, while CCCP at 1–5 ? 10^–6M, NH₄Cl at 5 ? 10^–2 M and DNP at 10^–4 M at pH 7.0stimulated LPC. PMS at 10^–4 M stimulated LPC and couldinduce LPC which was completely inhibited by DCMU. These factssuggest that LPC is related to noncyclic and cyclic electronflows. The influences of light and dark conditions and various metabolicinhibitors (DCMU, DNP, CCCP, NH₄Cl) on ATP level have been investigated.No significant difference in the ATP level was observed betweencells in the light and dark. DNP at 10^–4 M (pH 5.5) andCCCP at 5 ? 10^–6 M decreased the ATP level significantly,while DCMU and NH₄Cl only slightly. Good correlation was notfound between the total ATP level and LPC in Spirogyra. LPC occurred even when the external medium contained only asingle salt such as KCl, NaCl or CaSO₄. LPC was also recorded in chloroplasts in situ and in vitro.The mode of LPC of chloroplasts was quite different from thatof the cell. On illumination, the chloroplast potential changedvery rapidly and transiently in the positive direction thenrecovered spontaneously to almost the original potential level. Possible causes of LPC are discussed in relation to the electrogenicion pump. ¹ Present address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Bunkyo, Tokyo 113, Japan. (Received November 9, 1977; )