Single chloride-permeable channels of large conductance in cultured cardiac cells of new-born rats

Large conductance channels were observed in the membrane of cultured cardiac cells of newborn rats studied with the patch-clamp technique in cell-attached and inside-out configurations. These channels were observed in 4% of the patches. In the cell-attached configuration they exhibited outward rectification and partial inactivation. In the inside-out configuration no rectification occurred but inactivation was present, mainly during hyperpolarizations. Two channels with large single unit conductances (400–450 pS) and one with a smaller conductance (200–250 pS) were frequently observed in the same patch. The two large channels generally had different kinetics. Under steady-state conditions the opening probability of the faster channel appeared to be voltage-independent. The slower channel was activated by depolarization. In asymmetrical solutions the permeability ratios P _Na/P _Cl were 0.03 and 0.24 for the larger and smaller channels, respectively; corresponding values for P _Ba/P _Cl were 0.04 and 0.09. It is proposed that in cardiac membranes the chloride permeability system is composed of widely dispersed microclusters forming grouped channels of different types and sizes.     

Patch-clamp study of isolated taste receptor cells of the frog

Summary Taste discs were dissected from the tongue ofR. ridibunda and their cells dissociated by a collagenase/low Ca/mechanical agitation protocol. The resulting cell suspension contained globular epithelial cells and, in smaller number, taste receptor cells. These were identified by staining properties and by their preserved apical process, the tip of which often remained attached to an epithelial (associated) cell. When the patch pipette contained 110mm KCl and the cells were superfused with NaCl Ringer's during whole-cell recording, the mean zero-current potential of 22 taste receptor cells was –65.2 mV and the slope resistance 150 to 750 M. Pulse-depolarization from a holding voltage of –80 mV activated a transient TTX-blockable inward Na current. Activation became noticeable at –25 mV and was half-maximal at –8 mV. Steady-state inactivation was half-maximal at –67 mV and complete at –50 mV. Peak Na current averaged –0.5 nA/cell. The Ca-ionophore A23187 shifted the activation and inactivation curve to more negative voltages. Similar shifts occurred when the pipette Ca was raised. External Ni (5mm) shifted the activation curve towards positive voltages by 10 mV. Pulse depolarization also activated outward K currents. Activation was slower than that of Na current and inactivation slower still. External TEA (7.5mm) and 4-aminopyridine (1mm) did not block, but 5mm Ba blocked the K currents. K-tail currents were seen on termination of depolarizing voltage pulses. A23187 shifted theI _K(V)-curve to more negative voltages. Action potentials were recorded when passing pulses of depolarizing outward current. Of the frog gustatory stimulants, 10mm Ca caused a reversible 5-to 10-mV depolarization in the current-clamp mode. Quinine (0.1mm, bitter) produced a reversible depolarization accompanied by a full block of Na current and, with slower time-course, a partial block of K currents. Cyclic AMP (5mm in the external solution or 0.5 m in the pipette) caused reversible depolarization (to –40 to –20 mV) due to partial blockage of K currents, but only if ATP was added to the pipette solution. Similar responses were elicited by stimulating the adenylate cyclase with forskolin. Blockage of cAMP-phosphodiesterase enhanced the response to cAMP. These results suggest that cAMP may be one of the cytosolic messengers in taste receptor cells. Replacement of ATP by AMP-PNP in the pipette abolished the depolarizing response to cAMP. Inclusion of ATP--S in the pipette caused slow depolarization to –40 to –20 mV, due to partial blockage of K currents. Subsequently, cAMP was without effect. The remaining K currents were blockable by Ba. These results suggest that cAMP initiates phosphorylation of one set of K channels to a nonconducting conformation.     

Effects of reagents modifying carboxyl groups on the gating current of the myelinated nerve fiber

Summary K⁺ channels in inside-out patches from hamster insulin tumor (HIT) cells were studied using the patch-clamp technique. HIT cells provide a convenient system for the study of ion channels and insulin secretion. They are easy to culture, form gigaohm seals readily and secrete insulin in response to glucose. The properties of the cells changed with the passage number. For cell passage numbers 48 to 56, five different K⁺-selective channels ranging from 15 to 211 pS in symmetrical 140mm KCl solutions were distinguished. The channels were characterized by the following features: a channel with a conductance (in symmetrical 140mm KCl solutions) of 210 pS that was activated by noncyclic purine nucleotides and closed by H⁺ ions (pH=6.8); a 211 pS channel that was Ca²⁺-activated and voltage dependent; a 185 pS channel that was blocked by TEA but was insensitive to quinine or nucleotides; a 130 pS channel that was activated by membrane hyperpolarization; and a small conductance (15 pS) channel that was not obviously affected by any manipulation. As determined by radioimmunoassay, cells from passage number 56 secreted 917±128 ng/mg cell protein/48 hr of insulin. In contrast, cells from passage number 77 revealed either no channel activity or an occasional nonselective channel, and secreted only 29.4±8.5 ng/mg cell protein/48 hr of insulin. The nonselective channel found in the passage 77 cells had a conductance of 25 pS in symmetrical 140mm KCl solutions. Thus, there appears to be a correlation between the presence of functional K⁺ channels and insulin secretion.     

The effect of excitation on the rate of respiration in the liverwort Conocephalum conicum

Simultaneous measurements were taken of the electrical activity and the rate of respiration of thalli of Conocephalum conicum L. stimulated electrically and mechanically (by cutting). The measurements of the rate of respiration employed a modified Warburg apparatus for O₂ consumption and an infra-red gas analyzer with computer recording and data processing for CO₂ evolution. The action potential, produced by either a cut (a damaging stimulus) or an electrical stimulus (a non-damaging stimulus), caused a transient rise in the rate of respiration. The course of changes in the rate of respiration depends on the character of the excitation and the area of the thallus covered by it. If stimulation does not produce excitation, the increase in the rate of respiration does not take place, regardless of the magnitude and type of the stimulus applied.     

Electrical recording and ultrastructure of stylet penetration by the greenhouse whitefly

Earlier studies have indicated that interior (physical and/or chemical) properties of a plant may be responsible for feeding-site selection by the greenhouse whitefly, Trialeurodes vaporariorum (Westw.). In order to study the process of feeding-site selection further, stylet-penetration activities and the pathway followed by the stylets in host-plant tissue were investigated using a DC electrical recording method and transmission electron microscopy (TEM). Penetrating whiteflies attached to a gold wire were included in an electrical circuit to record electrical penetration graphs (EPGs). Seven EPG patterns have been distinguished, five of which could be correlated with components of the stylet-penetration process: 1) one with penetration of the leaf surface, 2) one with intercellular penetration and salivary-sheath secretion, 3) one with sieve element penetration and ingestion, 4) one with short penetration of a cell, and 5) one with xylem penetration. The stylet pathway is almost completely intercellular before the phloem is reached and in contrast to aphids, brief symplast punctures are very rare. In general, it takes T. vaporariorum more than half an hour from the start of a penetration to reach a sieve element. Rejection of feeding sites occurs within a few minutes of penetration by adult whiteflies, a time span in which stylets are presumed to penetrate just beyond the epidermis. Properties of the apoplast close to the leaf surface seem therefore to play a major role in feeding-site selection.

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Résumé De précédentes études ont montré que les propriétés internes (physiques et/ou chimiques) d'une plante peuvent induire la sélection du site de nutrition de la mouche blanche de serres, Trialeurodes vaporariorum (Westw.). Afin d'étudier plus avant le processus de sélection du site de nutrition, les activités de piqûre et le chemin suivi par le stylet dans les tissus de la plante-hôte ont été étudiés par une méthode d'enregistrement électrique en courant continu ainsi que par microscopie à transmission d'électrons (TEM). Des aleurodes en activité de piqûre attachées à un fil d'or ont été incluses dans un circuit électrique pour enregistrer des graphes de pénétration électriques (EPG). Sept motifs d'EPG ont été distingués, dont cinq peuvent être corrélés aux composantes du processus de pénétration du stylet: 1) un avec pénétration de la surface foliaire, 2) un avec pénétration interecellulaire et sécrétion d'une gaine de salive, 3) un avec pénétration du phloème, 4) un avec courte pénétration d'une cellule, et 5) un avec pénétration du xylème. Le parcours du stylet est presque entièrement intercellulaire avant que le phloème soit atteint. Contrairement aux pucerons, les ponctions brèves dans le symplasme sont rares. Généralement, T. vaporariorum met plus d'une demi-heure, à partir du début d'une piqûre, pour atteindre un vaisseau. Le rejet des sites de nutrition par les aleurodes adultes se passe quelques minutes après la pénétration du stylet; pendant ce laps de temps, le stylet pénétrerait juste sous l'épiderme. Le rôle des propriétés de l'apoplaste près de la surface foliaire semble donc majeur dans la sélection des sites de nutrition.

     

射击过程中主要生理特征的研究

八名射击运动员(手枪2人,步枪6人),在实弹射击训练中,连续同步地记录了脑电、心电、心率、阻抗呼吸波。同时记录了受试者持枪稳定的程度。 分析表明,射击环数是五项独立无关的指标综合作用的结果。本文首次对射击时生理指标和射击环数进行系统辨识建模分析,求出每个人的系统参数_i值。找出了每人射击时最佳生理参数,为指导射击练习和反馈训练,提供了客观生理依据。 本文设计的激光光点录相方法,可反映持枪稳定的程度,简单、方便,可在射击训练中采用。     

Membrane potentials as an indication for plant cell penetration by aphid stylets

Electrical penetration graphs (EPGs) of aphids on plants demonstrate distinct periods of lowered potential level: the potential drop (pd). Such pds are produced frequently during the stylet pathway to the phloem. Experimental evidence supports the hypothesis that the pd corresponds with a stylet puncture of a (epidermal or mesophyll) cell membrane. The intracellular potentials of-100 to-180 mV are thought to be measured thereby with the stylets acting as microelectrodes. The short pd of 5–15 s can be described as a sequence of three distinct phases. Besides the short pd, occurring during pattern B and C, long pds are produced during the complete pattern D+E. Pattern D+E may occur on the potential level of the pd (abbr.: D+E (pd)) and on the potential level of the preceding pattern C (abbr.: D+E(c)). Pattern D+E(pd) seems to be related to sieve element penetration, at least in a number of cases. Both pds, short and long, are produced on host and non-host plants, on susceptible and resistant cultivars, using several aphid species.

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Potentiels membraneux comme indication pour des pénétrations intracellulaires des plantes par les stylets des aphides

Résumé L'enrégistrement électrique de la pénétration du stylet des aphides dans les tissus de la plante se caracterise par des périodes distinctes de chute de potentiel (c.p.). Ces c.p. existent fréquemment au cours du trajet du stylet vers le phloème. Une évidence expérimentale soutient l'hypothèse de la correspondance entre la c.p. et la piqûre de la membrane des cellules épidermales et parenchymateuses. Les potentiels intracellulaires de-100 à-180 mV pourraient être mesurés par l'intermédiaire des stylets comme microélectrodes. Les. c.p. brèves, de 5 à 15 s peuvent être décrites comme des séquences composées de 3 phases distinctes. Outre les c.p. brèves pendant les ondes B et C, les pucerons produisent des c.p. durables qui se maintiennent au cours des ondes D+E. Ou bien l'onde D+E peuve apparaite au niveau de potentiel de c.p. (D+E(cp)), ou au niveau de potentiel de l'onde C précédente (D+E(c)). L'onde D+E(cp) semble être reliée à la pénétration des vaisseaux conducteurs, du moins dans certain cas. Les c.p. brêves et durables sont produits sur les plantes hôtes et non-hôtes chez plusiers espèces d'aphids.

     

Control of K+ conductance by cholecystokinin and Ca2+ in single pancreatic acinar cells studied by the patch-clamp technique

Summary The effect of cholecystokinin (CCK) and internal Ca²⁺ on outward K⁺ current in isolated pig pancreatic acinar cells has been investigated using the patch-clamp method for whole-cell current recording under voltage-clamp conditions. CCK (2 × 10^–10 M) applied to the bath evoked a marked increase in the outward K⁺ current associated with depolarizing voltage steps, and this effect was fully reversible and acutely dependent on the presence of external Ca²⁺. When strongly buffered Ca²⁺-EGTA solutions were used inside the cells CCK failed to evoke an effect. Increasing the internal Ca²⁺ concentration ([Ca²⁺] _i ) from 5 × 10^–10 M to 10^–7 and 5 × 10^–7 M mimicked the effect of CCK. It would appear therefore that CCK controls K⁺ conductance in the acinar cells via changes in the internal free ionized Ca²⁺ concentration.     

Effects of antidiuretic hormone on cellular conductive pathways in mouse medullary thick ascending limbs of Henle: II. Determinants of the ADH-mediated increases in transepithelial voltage and in net Cl− absorption

Summary Cellular impalements were used in combination with standard transepithelial electrical measurements to evaluate some of the determinants of the spontaneous lumen-positive voltage,V _e , which attends net Cl^– absorption,J _Cl ^net , and to assess how ADH might augment bothJ _Cl ^met andV _e in the mouse medullary thick ascending limb of Henle microperfusedin vitro. Substituting luminal 5mm Ba⁺⁺ for 5mm K⁺ resulted in a tenfold increase in the apical-to-basal membrane resistance ratio,R _c /R _bl , and increasing luminal K⁺ from 5 to 50mm in the presence of luminal 10^–4 m furosemide resulted in a 53-mV depolarization of apical membrane voltage,V _a . Thus K⁺ accounted for at least 85% of apical membrane conductance. Either with or without ADH. 10^–4 m luminal furosemide reducedV _e andJ _Cl ^net to near zero values and hyperpolarized bothV _a andV _bl , the voltage across basolateral membranes; however, the depolarization ofV _bl was greater in the presence than in the absence of hormone while the hormone had no significant effect on the depolarization ofV _a , Thus ADH-dependent increases inV _b were referable to greater depolarizations ofV _bl in the presence of ADH than in the absence of ADH 68% of the furosemide-induced hyperpolarization ofV _a was referable to a decrease in the K⁺ current across apical membranes, but, at a minimum, only 19% of the hyperpolarization ofV _bl could be accounted for by a furosemide-induced reduction in basolateral membrane Cl^– current. Thus an increase in intracellular Cl^– activity may have contributed to the depolarization ofV _bl during net Cl^– absorption, and the intracellular Cl^– activity was likely greater with ADH than without hormone. Since ADH increases apical K⁺ conductance and since the chemical driving force for electroneutral Na⁺,K⁺,2Cl^– cotransport from lumen to cell may have been less in the presence of ADH than in the absence of hormone, the cardinal effects of ADH may have been to increase the functional number of both Ba⁺⁺-sensitive conductance K⁺ channels and electroneutral Na⁺,K⁺,2Cl^– cotransport units in apical plasma membranes.