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Biomedical subjects

M Iino

Publications and source records attributed to M Iino.

At least 163 records · Page 9Linked to original sources
PubMed1989

Change in calcium permeability caused by quinolinic acid in cultured rat hippocampal neurons.

The calcium permeability of receptor channels activated by quinolinic acid (QUIN) in cultured rat hippocampal neurons was investigated using the whole-cell voltage-clamp method. In Na+-free, 10 mM Ca2+ solution with the internal solution containing 165 mM Cs+, QUIN elicited prominent inward currents at -60 mV, and the reversal potential of the QUIN-induced current was -5.8 +/- 1.2 mV, indicating that QUIN-activated channels are highly permeable to Ca2+ (permeability ratio PCa2+/PCs+ = 5.9). This result was substantiated by microfluorometry using fura-2, which revealed that QUIN caused a marked increase in the intracellular Ca2+ concentration even after the voltage-dependent Ca2+ channels had been suppressed by La3+.

Animals↗
PubMed1989

Three types of voltage-dependent calcium current in cultured rat hippocampal neurons.

Voltage-dependent calcium (Ca2+) currents in cultured rat hippocampal neurons were studied with the whole-cell recording mode of the patch-clamp technique. On the basis of the voltage-dependence of activation, kinetics of inactivation and pharmacology, 3 types of Ca2+ currents were distinguished. The low-threshold Ca2+ current (Il) was activated at -60 mV, and completely inactivated during a 100-ms depolarization to -40 mV (time constant: tau = 16 +/- 1 ms). The high-threshold currents (Ih), which were activated at -20 mV, could be separated into two types. The high-threshold, fast inactivating current (Ih,f) decayed quickly during a maintained depolarization (tau = 33 +/- 3 ms at 0 mV), whereas the high-threshold, slowly inactivating current (Ih,s) decayed with a much slower time constant (tau = 505 +/- 42 ms at 0 mV). The inactivations of Ih,f and Ih,s exhibited different time- and voltage-dependencies. Nickel ions (Ni2+, 25 microM) markedly suppressed Il, but little affected Ih. Cadmium ions (Cd2+, 10 microM) almost completely suppressed Ih, but left a small amount of Il. Lanthanum ions (La3+, 10 microM) almost completely suppressed both Il and Ih. Ih,s was sensitive to block by the dihydropyridine antagonist nicardipine (10 microM).

Animals↗
PubMed1989

Ion channels activated by quinolinic acid in cultured rat hippocampal neurons.

The membrane responses to quinolinic acid, an excitotoxic brain metabolite, were studied in cultured rat hippocampal neurons with the patch-clamp technique. In the whole-cell recording mode, pressure applications of quinolinic acid elicited inwardly directed membrane currents over a membrane potential range of -60 to -5 mV. The current response reversed at about 0 mV. The current-voltage (I-V) relation of the response had a negative slope conductance at membrane potentials more negative than -40 mV. On removal of Mg2+ from the extracellular solution, the current response showed no region of negative slope conductance at potentials more positive than -60 mV. In Mg2+-free solution applications of quinolinic acid elicited discrete pulse-like current flows through the outside-out membrane patch. The single channel conductance was 40-46 pS over a membrane potential range of -40 to -80 mV, and 50-55 pS at membrane potentials more positive than +30 mV, showing an outward rectification. These values of the single channel conductance were similar to those of the main conducting state of the channels activated by N-methyl-D-aspartate (NMDA). The responses to quinolinic acid were completely suppressed by the NMDA receptor antagonist (+/-)-2-amino-5-phosphonovaleric acid. The results indicate that quinolinic acid selectively activates NMDA receptors in the cultured rat hippocampal neurons.

2-Amino-5-phosphonovalerate↗
PubMed1989

Calcium-induced calcium release mechanism in guinea pig taenia caeci.

Fura-2 was used to measure the amount of Ca released from the intracellular Ca store of a saponin-skinned smooth muscle fiber bundle of the guinea pig taenia caeci (width, 150-250 microns) placed in a capillary cuvette at 20-22 degrees C. The amount of Ca actively loaded into the store was assayed when released by the application of 50 mM caffeine and/or 10 microM inositol 1,4,5-trisphosphate (IP3) in the absence of ATP, and was found to have a biphasic dependence on the loading [Ca2+] with a peak near pCa 6. After Ca loading at pCa 6, IP3 released almost all the releasable Ca, whereas caffeine discharged Ca from only approximately 40% of the store. The maximum amount of Ca in the store was some 220 mumol/liter cell water. Ca in the caffeine-releasable store was released approximately exponentially to zero with time when Ca2+ was applied in the absence of ATP, and the rate constant of the Ca-induced Ca release (CICR) increased steeply with the concentration of Ca2+ applied. Increase in [Mg2+] (0.5-5.0 mM) or decrease in pH (7.3-6.7) shifted the relation between pCa and the rate of CICR roughly in parallel toward the lower pCa. An adenine nucleotide increased the rate of the CICR, but it did not change the range of effective [Ca2+]. 5 mM caffeine greatly enhanced the CICR mechanism, making it approximately 30 times more sensitive to [Ca2+]. However the drug had no Ca-releasing action in the absence of Ca2+. Procaine in millimolar concentrations inhibited the rate of the CICR. These properties are similar to those of the skeletal muscle CICR and ryanodine receptor channels. Rates of the CICR under a physiological ionic milieu were estimated from the results, and a [Ca2+] greater than 1 microM was expected to be necessary for the activation of the Ca release. This Ca sensitivity seems too low for the CICR mechanism to play a primary physiological role in Ca mobilization, unless assisted by other mechanisms.

Adenine Nucleotides↗
PubMed1989

The occurrence of a ca-dependent period in the red light-induced late g1 phase of germinating adiantum spores.

The first cell cycle of Adiantum spores, which is induced by red light (R), was studied with regard to its temporal dependence on Pfr (the active form of phytochrome) and Ca(2+). Responses were quantified with increases of the spore content of DNA, thus limiting the investigation to the reactions taking place before the S phase of the cell cycle (i.e. during G0/G1/S transitions). Spores hydrated for more than 2 days in the standard medium (includes 1 millimolar free Ca(2+)) showed, after stimulation with a saturating R pulse, an increase of DNA beginning at about 25 hours and saturating at about 55 hours. Reversal by far-red light of the inductive effect of R was used to examine the temporal requirement for Pfr. Spores became dependent on the supply of external Ca(2+) when incubated in a low Ca medium (32 nanomolar free Ca(2+) with 10 millimolar EGTA); this culture condition was used, after observing that the DNA increase occurs similarly if Ca(2+) is supplied after the R pulse, to examine the temporal requirement for external Ca(2+). It was concluded that the G1 phase of the spore is separated into three subphases: (a) the Pfr-dependent period which immediately follows the R pulse and varies among individual spores from a few to about 25 hours, (b) the Ca(2+)-dependent period (about 10 hours) which occurs immediately before the S phase, and (c) a gap (15-20 hours) between the two periods. In the Ca(2+)-dependent period, spores require the presence of extracellular Ca(2+). This period occurs only during a determined time after the R pulse, and the competence of spores to enter the S phase is lost sharply if external Ca(2+) is not available continuously during this period.

Journal Article↗
PubMed1989

[Silent period and initial occlusal sliding time in patients with premature contacts].

This study was designed to examine the relationship between frequency of silent period and initial occlusal sliding time. The subjects consisted of three volunteers with normal occlusal contacts and three patients with premature contacts. Electromyograms of the bilateral masseter muscles, initial occlusal contacts and jaw movements during the habitual tapping (20-25) were synchronously recorded and replayed using Takamatsu's technique. Results were as follows: 1. The frequency of silent period in the bilateral masseter muscles was 95-100% in subjects with normal occlusal contacts and 34-53% in patients with premature contacts. 2. The silent period latency in three normal subjects was 8.9 +/- 1.3 msec in the left masseter and 13.9 +/- 2.2 msec in the right masseter. The silent period latency in three patients with premature contacts was 12.4 +/- 2.6 msec in the left masseter and 13.9 +/- 8.2 msec in the right masseter. 3. The duration of silent period in three normal subjects was 12.4 +/- 2.6 msec in the left masseter and 11.1 +/- 3.7 msec in the right masseter. The duration of silent period in three patients with premature contacts was 9.1 +/- 1.7 msec in the left masseter and 11.1 +/- 5.6 msec in the right masseter. 4. Initial occlusal sliding time in three subjects with normal occlusal contacts was less than 30 msec, and 98% of all slidings lasted for less than 15 msec. Initial occlusal sliding times in patients with premature contacts were distributed between 6 and 80 msec (40%: 6 to 15 msec, 60%: greater than 15 to 80 msec).(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Occlusion, Traumatic↗
PubMed1988

Use of ryanodine for functional removal of the calcium store in smooth muscle cells of the guinea-pig.

Calcium store of the skinned fibers of the guinea-pig portal vein, pulmonary artery and taenia caeci consisted of two classes: one with both Ca-induced Ca release (CICR) and inositol 1,4,5-trisphosphate (IP3)-induced Ca release (IICR) mechanisms (S alpha) and the other only with IICR mechanisms (S beta). Ryanodine, applied during the CICR was activated, locked the CICR channels open, but the drug had practically no effect on the IICR mechanism. Thus, after the ryanodine treatment the Ca store with the CICR (S alpha) lost its capacity to hold Ca. Changes in the agonist-evoked contraction of intact muscle due to the ryanodine treatment suggest that agonists release Ca from S alpha which produces the initial phase of contractures.

Alkaloids↗
PubMed1988

Pulse-induced phototropisms in oat and maize coleoptiles.

Phototropisms induced by a pulse (1-30 seconds) of blue light in red-light-grown coleoptiles of oats (Avena sativa L.) and maize (Zea mays L.) were investigated in terms of fluence-response relationships and time courses. Phototropic stimulation was made by a laser beam (457.9 nanometers), allowing application of high-fluence pulses. The phototropic fluence-response curves for oats and maize revealed two peaks in the positive range, thus indicating the occurrence of two separable pulse-induced positive responses. The response at low fluences corresponded to the ;first positive curvature.' The response at high fluences was very small in oats, but was large in maize. Reciprocity was valid in this high-fluence response (tested only for maize), indicating that it is distinct from the so-called ;second positive curvature.' In oats, the trough between the two positive responses fell into the negative range. This negative response, corresponding to the ;first negative curvature,' showed time courses distinct from those of ;first positive curvature:' the negative response was induced after a longer time lag and developed with a more gradual increase of the rate of bending. The maximal rate of the negative response was as high as one-half of that of first positive curvature. In maize, the trough between the two responses was in the positive range, and the time-course result revealed no apparent response counteracting the positive responses. Physiological and ecological implications of the pulse-induced phototropisms are discussed.

Journal Article↗
PubMed1987

Calcium dependent inositol trisphosphate-induced calcium release in the guinea-pig taenia caeci.

The properties of the Ca stores in the skinned fiber bundles of the guinea-pig taenia caeci were studied by a novel method to measure Ca released from the stores using a fluorescent Ca indicator, fura-2. It is found that the capacity of the Ca stores amounts some 170 mumoles/liter cell water. There are at least two Ca release mechanisms, Ca-induced Ca release (CICR) and Ca release induced by inositol-1,4,5-trisphosphate (IP3). Only about a half of the Ca is released by the Ca-induced Ca release, while IP3 releases most of the Ca. The rate of the IP3-induced Ca release is found to be strongly enhanced by submicromolar concentrations of Ca2+.

Adenosine Triphosphate↗
PubMed1986

Can lateral redistribution of auxin account for phototropism of maize coleoptiles?

Elongation growth of intact, red-light grown maize (Zea mays L.) coleoptiles was studied by applying a small spot of an indole acetic acid (IAA)-lanolin mixture to the coleoptile tip. We report that: (a) endogenous auxin is limiting for growth, (b) an approximately linear relation holds between auxin concentration and growth rate over a range which spans those rates occurring in phototropism, and (c) an auxin gradient established at the coleoptile tip is well sustained during its basipetal transport. We argue that the growth differential underlying coleoptile phototropism (first-positive curvature) can be explained by redistribution of auxin at the coleoptile tip.

Journal Article↗
PubMed1985

Kinetic properties of the blue-light response of stomata.

The stomatal response to blue light was analyzed with gas-exchange techniques in Commelina communis L. leaves by using high-fluence-rate short pulses. Pulses of blue light were given under a background of high-fluence-rate red light, which maintained photosynthesis at near saturation and stomatal conductance at a steady state. A single blue light pulse of 1-100 sec induced an increase in stomatal conductance, which peaked after 15 min and then returned to the initial steady-state level within 50-60 min after the pulse. The response could be repeatedly induced in the same leaf. Red light pulses on a red background did not induce any comparable response. The stomatal response quantified by integrating the conductance increases after pulse application approached saturation with increasing pulse duration (t((1/2)) approximately 9 sec with 250 mumol.m(-2).sec(-1) of blue light). After a saturating pulse, sensitivity to a second pulse was restored slowly. This recovery response, quantified from the conductance increases caused by the two pulses, approached saturation with a t((1/2)) of approximately 9 min. These results were used to test a model in which a molecular component in the sensory transduction process is considered to exist in two interconvertible forms, A and B. If B is the physiologically active form inducing stomatal opening, then A is the inactive form. The A to B conversion is a light-induced reaction and the B to A conversion is a thermal reaction. Rate constants for these reactions were estimated from single- and double-pulse experiments (at a fluence rate of 250 mumol.m(-2).sec(-1), k(1) = 0.075 sec(-1); thermal rate constant k(d) = 0.0014 sec(-1)), allowing the calculation of steady-state concentration of B under continuous irradiation. The calculated values accurately predicted the steady-state stomatal conductances under continuous blue light.

Journal Article↗
PubMed1984

Phototropic response of the stage I Phycomyces sporangiophore to a pulse of blue light.

Positive phototropic curvature of Phycomyces sporangiophores (stage I) induced by a short pulse (10 sec) of blue light has been characterized. The curvature response, measured 40 min after irradiation, increases with increasing fluences up to approximately 10(-4) J.m(-2); it then decreases and becomes nearly 0 at a fluence of approximately 10(-1) J.m(-2). The threshold fluence is found near 10(-7) J.m(-2), indicating over 1000-fold higher sensitivity than the first positive phototropism of grass coleoptiles. Positive curvature of the sporangiophore becomes detectable 5 min after irradiation and increases with time up to approximately 40 min. During the course of this curvature development, overall elongation growth of the sporangiophore is first stimulated and then inhibited. The relationship between the phototropic response and the response in overall elongation growth is discussed, and it is suggested that the primary mechanisms of these responses are distinct.

Journal Article↗
PubMed1984

Response selectivity of neocortical neurons to specific odors in the rabbit.

Odor responses of neocortical neurons in rabbits under light pentobarbital anesthesia were studied in a restricted area in the lateral half of the prefrontal cortex close to the frontal pole. A preevent cumulative sum chart provided a visual display of the change in unit discharge rate following each odor stimulation, and critical levels on each chart provided a visual display of statistical significance. The neocortical neurons studied were activated predominantly by biologically significant odors, such as feces, urine, and dry food. Of those same neurons, 90% failed to respond to pure-chemical odors, and no neurons were found that responded to pure-chemical odors alone. Some neurons responded exclusively to one of the animal-product odors. Some odor-sensitive neurons were affected by electrical stimulation of the mediodorsal thalamic nucleus. Responses to the animal-product odors were observed after ablation of the trigeminal and/or vomeronasal inputs. The responses to these pheromone-like substances are discussed in the context of a central role for odor-sensitive neocortical neurons in cognitive aspects of discrimination of specific odor patterns in the mammals.

Animals↗