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N Fujishiro

Publications and source records attributed to N Fujishiro.

At least 19 recordsLinked to original sources
PubMed2002

Role of ATP decrease in secretion induced by mitochondrial dysfunction in guinea-pig adrenal chromaffin cells.

The mechanism related to mitochondrial dysfunction-induced catecholamine (CA) secretion in dispersed guinea-pig adrenal chromaffin cells was investigated using amperometry and confocal laser microscopy. Application of CCCP, which does not stimulate generation of reactive oxygen species (ROS), reversibly induced CA secretion, whereas application of either cyanide or oligomycin (OL), a stimulator for ROS, enhanced CA secretion to a smaller extent. The CCCP-induced secretion was abolished by removal of external Ca2+ ions and was markedly diminished by D600. The mitochondrial membrane potential, measured using rhodamine 123, was rapidly lost in response to CCCP, but did not change noticeably during a 3 min exposure to OL. Prior exposure to OL markedly facilitated depolarization of the mitochondrial membrane potential in response to cyanide. The mitochondrial inhibitors rapidly produced an increase in Magnesium Green (MgG) fluorescence in the absence of external Ca2+ and Mg2+ ions, an increase that was larger in the cytoplasm than in the nucleus. The rank order of potency in increasing MgG fluorescence among the inhibitors was similar to that in increasing secretion. Thus, mitochondrial inhibition rapidly decreases [ATP] and the mitochondrial dysfunction-induced secretion is not due to ROS generation or to mitochondrial depolarization, but is possibly mediated by a decrease in ATP.

Adenosine Triphosphate↗
PubMed2000

Pituitary adenylate cyclase-activating polypeptide may function as a neuromodulator in guinea-pig adrenal medulla.

The role of pituitary adenylate cyclase-activating polypeptide (PACAP) in catecholamine secretion from dissociated adrenal chromaffin cells of the guinea-pig was investigated using amperometry, the patch clamp technique and immunochemistry. Pretreatment of adrenal chromaffin cells with 0.3-10 nM PACAP for 2 min resulted in enhancement of nicotine- and muscarine-induced secretions in either the presence of external Ca2+ ions or nominally Ca2+-free solution, with no change in basal secretion or the holding current at -60 mV in most of the cells tested. Pretreatment with PACAP augmented the muscarine-induced non-selective cation current, but did not affect the muscarine-induced outward current or nicotine-induced current. PACAP-induced enhancement of nicotine- and muscarine-induced secretions was suppressed by the simultaneous application of PACAP and the protein kinase inhibitors 100 microM HA1004 or 2 microM H89. Application of forskolin enhanced both muscarine- and nicotine-induced secretions, whereas application of a phorbol ester augmented the nicotine-induced secretion, but suppressed the muscarine-induced secretion in a reversible manner. Immunohistochemical analysis of adrenal medullae revealed that PACAP-like immunoreactivity was present in nerve fibres surrounding putative chromaffin cells. PAC1R-like immunoreactivity was distributed diffusely in the plasma membrane, whereas nicotinic ACh receptor-like immunoreactivity was concentrated at the plasma membrane near the nucleus, where the synapses were mainly localized. These observations suggest that PACAP in the guinea-pig adrenal medulla functions as a neuromodulator to facilitate ACh-induced secretion through a cAMP-protein kinase A-dependent pathway.

Adrenal Medulla↗
PubMed2000

Retardation of cation channel deactivation by mitochondrial dysfunction in adrenal medullary cells.

The mechanism for cyanide (CN) activation of a nonselective cation (NS) channel coupled with a muscarinic receptor in a guinea pig chromaffin cell was studied with the perforated-patch method. Bath application of a protein kinase inhibitor resulted in a dose-dependent inhibition of muscarine-induced current (I(M)) but had no apparent effect on the CN-induced current (I(CN)). On the other hand, production of I(CN) occluded muscarine activation of NS channels in an amplitude-dependent manner. Deactivation of I(M) after washout was retarded while I(CN) was also active, and the extent of the retardation increased with an increase in the relative production of I(CN) on muscarinic stimulation. Restoration of Na(+) pump activity from CN suppression was conspicuously retarded below 19-20 degrees C, and the apparent diminution of I(M) and I(CN) after washout was retarded in parallel with a decrease in temperature. The results suggest that CN activation of NS channels is due to suppression of deactivation of the channel.

Adrenal Medulla↗
PubMed1999

Na+ pump inhibition and non-selective cation channel activation by cyanide and anoxia in guinea-pig chromaffin cells.

1. Hypoxia and metabolic inhibition with cyanide (CN) evoke catecholamine secretion in adrenal chromaffin cells through depolarization. We elucidated mechanisms for a CN- or anoxia-induced inward (depolarization) current, using the perforated patch method. 2. Bath application of Ba2+ induced a dose-dependent inhibition of a muscarine-induced current (IMUS) and part of the CN-induced current (ICN) with an IC50 (concentration responsible for 50 % inhibition) of 1.3 mM. The Ba2+-sensitive component was estimated to comprise 58 % of the total ICN. 3. The Ba2+-resistant component of ICN tended to increase with shifts of membrane potential from -40 to 40 mV and was markedly suppressed by exposure to a K+-free solution or 200 microM ouabain, indicating that the majority of the Ba2+-resistant component of ICN is due to suppression of the Na+ pump current (Ipump). 4. The non-Ipump component of ICN diminished progressively in K+-free solution. Substitution of glucose for sucrose in a K+-free CN solution further diminished the CN potency to produce the non-Ipump component. 5. The I-V relationship for the non-Ipump component of ICN had a reversal potential of -3 and -47 mV at 147 and 5.5 mM Na+, respectively, and showed an outward rectification, indicating that the non-Ipump component of ICN is due to activation of non-selective cation channels. 6. Exposure to anoxia induced a current with an amplitude comparable to that of ICN, and the anoxia-induced current apparently occluded development of ICN. The anoxia-induced current diminished by ca 60 % in the absence of K+ and reversed polarity at 5 mV under K+-free conditions. 7. It is concluded that exposure to CN and to anoxia induces suppression of the Na+ pump and activation of non-selective cation channels, probably due to an ATP decrease resulting mainly from consumption by the Na+ pump.

Animals↗
PubMed1999

Wavelength dependence of the optically recorded action potentials in guinea pig atrial muscles.

The optically recorded action potentials of the frog atrial muscles which lack transverse tubules showed different features from those reported by Heiny and Vergara (Heiny JA, Vergara J. Optical signals from surface and T system membranes in skeletal muscle fibers. J Gen Physiol 1982;80:203-230) in skeletal muscles (Fujishiro N, Kawata H. The wavelength dependence of optically recorded action potentials in the atrial muscles of the bullfrog (Rana catesbeiana). Comp Biochem Physiol 1996;114A:153-157). We examined whether or not the differences were consistent in other atrial muscles which lack transverse tubules with guinea pig atrial muscles. Two dyes (merocyanine rhodanine and merocyanine oxazolone) were used, and the dependence of the maximum rising phase of the optical signals on the wavelength of the incident beam was analyzed. No dependence was observed between them, and this finding was consistent with the structure of the membrane system of the guinea pig atrial muscles. The optical signals recorded at 718 nm of the incident beam from the guinea pig atrial muscles which stained with merocyanine oxazolone showed a more prominent second rising phase after the initial rapid rising phase of the optical signal than that recorded in the frog atrial muscles. This phase was not observed in the optical signals recorded at other wavelengths. The features of the optically recorded action potentials in guinea pig atrial muscles were consistent with those recorded in frog atrial muscles. Nifedipine did not affect the second rising phase.

Action Potentials↗
PubMed1998

Hypoxia and cyanide induce depolarization and catecholamine release in dispersed guinea-pig chromaffin cells.

1. The perforated patch method and amperometry were used to determine whether the adrenal medullary cell itself is capable of sensing hypoxia and, if so, how such sensation is transduced to secretion of catecholamines (CA). 2. Exposure to hypoxia, cyanide (CN), or muscarine facilitated CA secretion from dissociated chromaffin cells. The CN-induced secretion was not affected by removal of glucose, indicating that the CN release is due to chemical hypoxia. 3. The secretions induced by CN and muscarine were markedly diminished by removal of Ca2+ ions or by application of Cd2+ or methoxyverapamil (D-600). 4. Cyanide and muscarine produced depolarizations with generation of action potentials and increased intracellular Ca2+ concentrations determined using the acetoxymethyl (AM) ester form of fluo-3 in the presence of external Ca2+ ions, but not in their absence. 5. Hypoxia and CN produced inward currents at an equilibrium potential for Cl- ions, irrespective of whether or not Na+ ions were present in the cells, and substitution of N-methyl-D-glucamine for 134 mM Na+ ions in the perfusate inhibited the CN current by 71 %. The reversal potential for the CN current was -24 mV in the standard perfusate. 6. The hypoxia-, CN- and muscarine-induced currents decreased in parallel with hyperpolarizations, and exposure to CN prevented muscarine, but not nicotine, from inducing a further inward current. 7. We conclude that hypoxia and CN induce CA secretion through depolarization and the subsequent activation of voltage-dependent Ca2+ channels and that this depolarization is due to opening of cation channels, which are possibly identical to muscarinic cation channels.

Adrenal Medulla↗
PubMed1996

Role and source of ATP for activation of nonselective cation channels by AlF complex in guinea pig chromaffin cells.

Intracellular dialysis with the solution containing the G protein activator, AlF complex, induced an inward nonselective cation current (INS) at -55 mV in chromaffin cells. Amplitudes of INS induced by dialysis with ATP-free AlF solutions progressively diminished as cells were pretreated with cyanide, a mitochondrial inhibitor. After a 10-min pretreatment, generation of INS by the AlF complex depended on exogenous ATP delivered from pipette solution. The relationship between amplitudes of INS and concentrations of MgATP was well expressed by a rectangular hyperbola with an EC50 of 0.265 mM. This result suggests that the cyanide treatment almost depleted ATP near the plasma membrane. On the other hand, a similar cyanide treatment of adrenal medullary preparations did not induce a marked decrease in cellular ATP content. GTP, ITP, or UTP could not substitute for ATP in generation of INS by the AIF complex. Similarly, the substitution of ATP with non- or poorly hydrolyzable ATP analogues did not aid in generating INS. Bath application of the kinase inhibitor, H-7 (100 microM), suppressed AlF-induced INS in a manner depending on intracellular Mg2+. We conclude that ATP is a prerequisite for generation of INS as a phosphoryl donor and that mitochondria is the main source of ATP.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1996

The wavelength dependence of optically recorded action potentials in the atrial muscles of the bullfrog (Rana catesbeiana).

The action potentials from frog atrial muscles that had been stained with either merocyanine rhodanine or merocyanine oxazolone dyes were recorded optically. Then the dependence of the maximum rising phase of the optically recorded action potential on the wavelength of the incident beam was analyzed. The atrial muscle stained with two kinds of dyes showed no wavelength dependence in the duration of the rising phase (defined in Fig. 1) in the maximum rising phase of the action potential. These results were consistent with the structure of the membrane system of the frog heart. However, for the atrial muscles stained with merocyanine oxazolone dye, the optical signals recorded at 718 nm of the incident beam showed a second rising phase after the initial rapid rising phase of the optical signal, and this phase was not observed in the optical signals recorded at other wavelengths.

Action Potentials↗
PubMed1996

Spectroscopic properties of fluorescence dye fura-2 with various divalent cations.

We examined the effects of divalent cations on the fluorescence excitation spectra of fura-2 from a 2 ml solution containing 1 microM fura-2 with an excitation wavelength of 300-425 nm and an emission wavelength of 500 nm. The fluorescence spectra in solutions of fura-2-Ca2+, fura-2-Ba2+, and fura-2-Sr2+ complexes show almost the same pattern. The dissociation constants (Kd) of Ba2+ and Sr2+ with fura-2 were 1.63 and 9.02 microM, respectively, and these values were higher than that of the Ca2+ complex (222 nM). The effect of Mg2+ binding on the fluorescence of fura-2 was quite small, and Mn2+ quenched the fluorescence of fura-2. The spectra of the fura-2-Ca2+ complex were changed by the co-existence of another divalent cation. Divalent cations competitively bind to the binding site of fura-2 and show the respective fluorescence spectra; consequently, the composed fluorescence spectra according to the respective Kd.

Cations↗
PubMed1995

Mg2+-dependent phosphatase as an inhibitory mediator of the nonselective cation current induced by aluminum fluoride in guinea-pig chromaffin cells.

Internal administration of the G protein activator, guanosine-5'-o-(3-thiotriphosphate) (GTP gamma S) or aluminum fluoride (AIF) complex, produced an inward nonselective cation current (INS) at -55 mV. This current was rapidly diminished under conditions of high intracellular Mg2+ ([Mg2+] = 979 microM), the half decay time (T1/2) being 80 to 100 s. As [Mg2+] in AlF solutions decreased from 400 to 12 microM, the maximum amplitude of AlF-induced INS became larger and the current was diminished more slowly. The AlF INS in the presence of 12 microM Mg2+ reversed polarity at about +9 mV, irrespective of the extent of decline. Bath application of muscarine produced a sustained INS in the absence of AlF complex, but in its presence, the overall current comprising a spontaneously developed INS and muscarine-induced INS was rapidly diminished. Addition of vanadate (0.5 mM) to 979 microM Mg2+ -containing AlF solution mimicked the effects of low Mg2+ solution. Inversely, addition of alkaline phosphatase (40 units/ml) to 12 microM Mg2+ AlF solution reproduced the effects of high Mg2+ solution. It is suggested that AlF complex deactivates INS through facilitating an apparent activity of Mg2+ -dependent phosphatase.

Aluminum Compounds↗
PubMed1995

A program for calculating the total concentrations of ligands and metals at any temperature, ionic strength and pH for solutions with a controlled metal concentration.

A program for calculating the total concentrations of ligands and metals at any temperature, ionic strength and pH for solutions with a controlled metal concentration was written in Quick-Basic. For the calculation, the absolute stability constants of ligands and the proton activity coefficient were corrected for temperature and ionic strength.

Algorithms↗
PubMed1994

Determination of the appropriate valence of 1,4-piperazinediethanesulfonic acid (PIPES) in physiological pH.

1,4-Piperazinediethanesulfonic acid (PIPES), a zwitterion buffer, was titrated with KOH to measure its pH and osmolality. Both pH and osmolality changes showed three phases, and two transition points coincided with pH 5.1 and 10.2. The second phase is important in biological reactions, and from the present results, the pK1 is 3.3 while pK2 is 6.85 at 20 degrees C. The slope of the osmolality curve was 2 mOsm per 1 mM KOH addition in the first and third phases, while it was 1 mOsm per 1 mM KOH in the second phase. The first phase indicates that +/- PIPES +/- changes to -PIPES +/- by the addition of KOH. In the second phase, additional KOH produces -PIPES-. PIPES acts as a divalent ion, at least, in the physiological pH range of around 7.0. Concentrations of -PIPES +/- and -PIPES- around the physiological pH range are calculated as follows. [formula: see text] The ionic strength of PIPES is calculated as follows. [formula: see text]

Alkanesulfonic Acids↗
PubMed1992

Tetanus responses under rapid bath solution change: electrotonic depolarization of transverse tubules may release Ca2+ from sarcoplasmic reticulum of Rana japonica skeletal muscle.

1. Single skeletal muscle fibers were transferred from a normal Ringer solution to Na+ ion free solution, and vice versa, and tetanus responses were recorded immediately after the transfer. 2. Fractional tetanus tension recorded immediately after the displacement from the Na+ ion free solution to normal Ringer solution was dependent on fiber diameter. 3. Diffusion of Na+ ions along the transverse tubules was simulated [apparent diffusion constant was 3.11 x 10(-6) (cm2/s)]. 4. Our results suggest that the electronic spreading of membrane potential, caused by an action potential in the transverse tubules, could release Ca2+ ions from sarcoplasmic reticulum.

Action Potentials↗