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M Wakui

Publications and source records attributed to M Wakui.

At least 73 records · Page 4Linked to original sources
PubMed1990

Receptor-activated cytoplasmic Ca2+ spiking mediated by inositol trisphosphate is due to Ca2(+)-induced Ca2+ release.

Receptor-mediated inositol 1,4,5-trisphosphate (Ins-(1,4,5)P3) generation evokes fluctuations in the cytoplasmic Ca2+ concentration ([Ca2+]i). Intracellular Ca2+ infusion into single mouse pancreatic acinar cells mimicks the effect of external acetylcholine (ACh) or internal Ins(1,4,5)P3 application by evoking repetitive Ca2+ release monitored by Ca2(+)-activated Cl- current. Intracellular infusion of the Ins(1,4,5)P3 receptor antagonist heparin fails to inhibit Ca2+ spiking caused by Ca2+ infusion, but blocks ACh- and Ins(1,4,5)P3-evoked Ca2+ oscillations. Caffeine (1 mM), a potentiator of Ca2(+)-induced Ca2+ release, evokes Ca2+ spiking during subthreshold intracellular Ca2+ infusion. These results indicate that ACh-evoked Ca2+ oscillations are due to pulses of Ca2+ release through a caffeine-sensitive channel triggered by a small steady Ins(1,4,5)P3-evoked Ca2+ flow.

Acetylcholine↗
PubMed1990

Intracellular aluminium inhibits acetylcholine- and caffeine-evoked Ca2+ mobilization.

The effect of intracellular aluminium on Ca2+ signalling in single internally perfused mouse pancreatic acinar cells was investigated by measurement of the Ca2(+)-dependent Cl- current using the patch-clamp whole-cell recording configuration. Acetylcholine (ACh) normally evoked a pulsatile Ca2(+)-dependent Cl- current, but when AlCl3 (1 mM) was present in the internal perfusion solution the ACh responses were virtually absent. When aluminium was acutely infused into the internal perfusion solution, the ACh-evoked Ca2+ signals and also the caffeine-evoked responses quickly disappeared, but the Ca2+ ionophore, ionomycin (100 nM), could still induce a large increase in the Cl- current. It is concluded that intracellular aluminium can abolish receptor-activated intracellular Ca2+ release probably by inhibition of Ca2(+)-induced Ca2+ release.

Acetylcholine↗
PubMed1990

Cytoplasmic Ca2+ oscillations evoked by acetylcholine or intracellular infusion of inositol trisphosphate or Ca2+ can be inhibited by internal Ca2+.

In single internally perfused mouse pancreatic acinar cells, changes in the free intracellular Ca2+ concentration ([Ca2+]i) were monitored by measuring the Ca2(+)-dependent transmembrane Cl- current under voltage-clamp conditions. Cytoplasmic Ca2+ oscillations were induced by external acetylcholine (ACh) application, internal infusion of inositol (1,4,5) trisphosphate or its non-metabolizable analogue inositol trisphosphorothioate or by intracellular Ca2+ infusion. Such [Ca2+]i oscillations could be rapidly inhibited by external application of the Ca2+ ionophore ionomycin (10-100 nM). Cytoplasmic Ca2+ oscillations could also be evoked by external caffeine (1 mM) application when the internal perfusion solution did not contain any Ca2+ chelator. In such cases intracellular Ca2+ infusion transiently abolished the [Ca2+]i oscillations. We conclude that although Ca2(+)-induced Ca2+ release is the cause of the ACh-evoked [Ca2+]i oscillations, there is also a negative feed-back since Ca2+ can inhibit Ca2+ release initiated by Ca2+.

Acetylcholine↗
PubMed1990

Cytoplasmic Ca2+ oscillations evoked by receptor stimulation, G-protein activation, internal application of inositol trisphosphate or Ca2+: simultaneous microfluorimetry and Ca2+ dependent Cl- current recording in single pancreatic acinar cells.

The effects of acetylcholine (ACh), cholecystokinin (CCK), internally applied GTP-gamma-S, inositol trisphosphate [Ins (1,4,5) P3] or Ca2+ on the cytoplasmic free Ca2+ concentration [( Ca2+]i) were assessed by simultaneous microfluorimetry (fura-2) and measurement of the Ca2(+)-dependent Cl- current (patch-clamp whole-cell recording) in single internally perfused mouse pancreatic acinar cells. ACh (0.1-0.2 microM) evoked an oscillating increase in [Ca2+]i measured in the cell as a whole (microfluorimetry) which was synchronous with oscillations in the Ca2(+)-dependent Cl- current reporting [Ca2+]i close to the cell membrane. In the same cells a lower ACh concentration (0.05 microM) evoked shorter repetitive Cl- current pulses that were not accompanied by similar spikes in the microfluorimetric recording. When cells did not respond to 0.1 microM ACh, caffeine (1 mM) added on top of the sustained ACh stimulus resulted in [Ca2+]i oscillations seen synchronously in both types of recording. CCK (10 nM) also evoked [Ca2+]i oscillations, but with much longer intervals between slightly broader Ca2+ pulses. Internal perfusion with 100 microM GTP-gamma-S evoked [Ca2+]i oscillations with a similar pattern. Ins (1,4,5) P3 (10 microM) evoked repetitive shortlasting spikes in [Ca2+]i that were only seen in the Cl- current traces, except in one small cell where these spikes were also observed synchronously in the microfluorimetric recording. Caffeine (1 mM) broadened these Ca2+ pulses. [Ca2+]i was also directly changed, bypassing the normal signalling process, by infusion of a low or high Ca2+ solution into the pipette.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1989

Pulsatile intracellular calcium release does not depend on fluctuations in inositol trisphosphate concentration.

Many hormones, neurotransmitters and growth factors evoke in their target cells oscillations in the free internal Ca2+ concentration [( Ca2+]i). In electrically non-excitable cells these fluctuations are due to periodic release of Ca2+ from intracellular reservoirs, stimulated by the internal messenger inositol trisphosphate (InsP3). Most models at present invoke fluctuating levels of InsP3 as a key component in generating the oscillations in [Ca2+]i. InsP3 injected into intact cells evokes irregular and transient oscillatory Ca2+-dependent current responses, but the intracellular InsP3 concentration is not constant in such experiments. Here we monitor changes in [Ca2+]i by measuring Ca2+-activated Cl- current in single internally perfused mouse pancreatic acinar cells and show that acetylcholine (ACh), acting through muscarinic receptors, evokes regular and repetitive current pulses which are mimicked by InsP3 applied through a patch pipette. To exclude the possibility that InsP3 is periodically phosphorylated or degraded, we replaced it by the non-metabolizable InsP3 analogue inositol trisphosphorothioate (InsPS3), which also evokes regular pulses of Ca2+-activated Cl- current. These effects are independent of external Ca2+, but abolished by high intracellular concentrations of a Ca2+-chelator. We conclude that repetitive pulses of intracellular Ca2+ release occur even when the concentration of InsP3 is constant.

Acetylcholine↗
PubMed1989

Depression of voltage-dependent Ca2+ current by noradrenaline in the guinea-pig vas deferens in tetraethylammonium medium.

The actions of noradrenaline (NA) on the smooth muscle of the guinea-pig vas deferens in tetraethylammonium (TEA) medium have been studied under constant-current and voltage-clamp conditions. The marked changes observed during exposure to NA are 1) slowness in the rising phase of the action potential, delay in the falling phase and reduction in the amplitude, and 2) depression of the voltage-dependent Ca2+ current with a negative shift of its reversal potential as well as with a reduction in its conductance. These findings might suggest that NA application stimulates the voltage-independent Ca2+ machinery, but suppresses the voltage-dependent Ca2+ machinery through membrane.

Action Potentials↗
PubMed1988

Two alpha-adrenergic contractions with different Ca2+ activation mechanisms in response to field nerve stimulation in the circular smooth muscle of guinea-pig vas deferens.

1. Two noradrenergic components of contraction were induced by field nerve stimulation of the circular smooth muscle of guinea-pig vas deferens. One component occurred during the stimulation (former-response) and the other component occurred after stimulation had ceased (after-response), with a distinct tension fall between these two responses. 2. The effects of stimulation frequency and duration upon these components were examined. 3. Prazosin (0.05-0.5 microM) suppressed both responses, whereas nifedipine (0.02 microM) suppressed only the after-response. 4. It is suggested that in this tissue there are two neurogenic alpha-adrenergic contractions which possess different Ca2+ activation mechanisms. The former-response is due to an increase in cytoplasmic Ca2+ concentration through a pathway independent of action potentials, while the after-response is attributed to action potentials arising as a secondary response to the released noradrenaline.

Animals↗
PubMed1988

D-600 sensitive and insensitive spontaneous contractions in the guinea-pig hepatic duct.

The mechanical properties of the longitudinally cut preparations of the guinea-pig hepatic duct were studied. About 42% of the preparations (18 of 43 preparations) showed spontaneous phasic contractions which were unaffected by either tetrodotoxin, guanethidine or atropine. About 60% of them exhibited phasic contractions which appeared at irregular frequencies in the same tissue and varied in size. This sort of contractions usually accompanied small contractions. In about 20%, contractions occurred constantly in frequency (about 6-14 every 10 min) and in size. The remaining 20% showed twitch-like contractions which occurred sporadically. These contractions were classified into two types depending upon the susceptibility to the Ca2+ entry blocker, D-600. D-600 (1-100 microM) strongly suppressed both regularly occurring contractions and twitch-like ones. On the other hand, the drug was ineffective on irregularly occurring contractions. The Ca2+ sources underlying these contractions were discussed.

Animals↗
PubMed1988

[Spontaneous regression of lung metastasis of renal cell carcinoma: a case report].

A chest X-ray tomography revealed a metastatic shadow in the left lung of a 56-year-old man with pathologically established right renal cell carcinoma. The shadow was found to be regressed to a fibrous lesion on the 18th day after radical nephrectomy. Because of non-A, non-B, hepatitis, the anticancer treatment with alpha-interferon and 1-(2-tetrahydrofuryl-5-fluorouracil) was started 40 days after the nephrectomy. At that time, only a fibrous lesion was noted at the site of lung metastatic shadow. At present, the patient remains free of disease for 21 months after nephrectomy.

Carcinoma, Renal Cell↗
PubMed1987

Lack of involvement of Ca2+ conductance change in ATP-induced depolarization of the guinea-pig vas deferens.

The double sucrose-gap method was used to examine the electrical responses of the guinea-pig vas deferens to ATP and their possible dependence on external Ca2+. Normally ATP induced a depolarization and an increase in membrane conductance and both effects were concentration-dependent. The reversal potential of the 10(-4) M ATP-induced depolarization was 27.1 mV positive to the resting membrane potential of the tissue. This value was quite similar to that previously obtained for the 3 X 10(-5) M ATP-induced depolarization. The smooth muscle membrane was depolarized by 5.9 mV in a Ca-free medium, in which ATP also caused a depolarization, associated with an increase in membrane conductance. The reversal potential of the depolarization induced by ATP (10(-4) M) in the Ca-free medium was 26.5 mV positive to the resting membrane potential. The results suggest that, in this tissue, ATP induces membrane depolarization with little effect on Ca2+ conductance.

Adenosine Triphosphate↗
PubMed1987

Involvement of cholinergic nerves in excitatory junction potentials through prejunctional nicotinic receptors in the guinea-pig vas deferens.

1. The effects of various drugs on excitatory junction potentials (EJPs) elicited by field stimulation of the longitudinal smooth muscle of the guinea-pig vas deferens were examined using the sucrose-gap method. 2. Field stimulation with a single pulse (1.0 ms, 20 Vcm-1) produced a depolarization of 3-7 mV. When a single pulse was repetitively applied, the depolarization showed summation, resulting in action potential firing. 3. Tetrodotoxin (1 microM) and guanethidine (1 microM) completely suppressed EJPs whilst propranolol (1 microM) or atropine (0.1 microM) did not affect them. Phentolamine (1 microM) slightly potentiated EJPs. 4. d-Tubocurarine (dTC) at lower concentrations (0.5-2 microM) suppressed EJPs, but at a higher concentration (20 microM) the drug little affected them. 5. Hexamethonium (C6) suppressed EJPs at low concentrations (0.5-5 microM), but potentiated them at a higher concentration (50 microM). 6. Either dTC or C6, each at a concentration of 0.5 microM, did not affect the depolarization induced by exogenously applied ATP or noradrenaline. 7. These results suggest that in this tissue cholinergic nerve activity can contribute to the magnitude of EJPs, and that this effect is mediated through nicotinic receptors.

Animals↗
PubMed1986

Dual excitatory actions of acetylcholine at the neuromuscular junction in the guinea-pig vas deferens.

The action of acetylcholine (ACh) on the smooth muscle of guinea-pig vas deferens was studied using the sucrose-gap method. ACh, when applied at a concentration of 10(-6) M, evoked a depolarization of the smooth muscle membrane which was slow in time course (slow depolarization). When ACh was applied at higher concentrations, another depolarization which was fast in time course (fast depolarization) occurred, overlapping the early part of the slow depolarization. The magnitudes of both depolarizations were concentration-dependent on ACh. TTX and adrenergic receptor antagonists had little effect on either depolarizations, while guanethidine and nicotinic receptor antagonists mainly suppressed the fast depolarization. In contrast, atropine suppressed the slow depolarization. The membrane conductance observed by current application, was reduced during the slow depolarization, and the reversal potential of the depolarization was 18.3 mV negative to the resting membrane potential. Whereas, the reversal potential of the fast depolarization was 27.6 mV positive to the resting membrane potential. This reversal potential was quite similar to that of the adenosine triphosphate (ATP)-induced depolarization, previously observed in the same tissue. From these observations, it is suggested that in the guinea-pig vas deferens, ACh acts on nicotinic receptors at the sympathetic postganglionic nerve terminal, causing the release mostly of a non-adrenergic transmitter, probably ATP. In addition, ACh also acts on muscarinic receptors on the smooth muscle membrane, inducing membrane depolarization resulting from a reduction of the membrane conductance to potassium ions.

Acetylcholine↗
PubMed1986

Possible interaction of cholinergic nerves with two different (pre and post) sites of the neuromuscular junction in guinea-pig vas deferens.

Effects of various drugs on the mechanical responses of the longitudinal smooth muscle of guinea-pig vas deferens evoked by ACh and field nerve stimulation were examined. ACh (28-280 microM) produced a contraction consisting of two phases. The first phase of the contraction was suppressed by guanethidine and by nicotinic antagonists. The second phase was suppressed only by atropine. Both phases were unaffected by TTX or prazosin. Field stimulation (0.1 msec, 40 Hz) evoked contractions which also consisted of two (early and late) phases. Guanethidine (0.1-1 microM) suppressed both phases whilst prazosin (1 microM) suppressed only the late phase. Atropine (0.1 microM) suppressed both phases whilst physostigmine (5 microM) potentiated both phases of field stimulation-evoked contractions. Pentolinium suppressed both phases of field stimulation-evoked contractions at low concentrations (2-10 microM), but potentiated them at a higher concentration (100 microM). dTC at a low concentration (0.5 microM) suppressed the early phase, but slightly enhanced the late phase of field stimulation responses. At a higher concentration (20 microM), dTC potentiated both phases of the response. Pentolinium and dTC did not affect the contractions induced by 90 mM-K ions, ATP or NA. These results suggest that cholinergic nerves possess an excitatory action not only directly at the smooth muscle but also at the noradrenergic nerve terminals. The role of each receptor is discussed further.

Adrenergic Fibers↗
PubMed1986

Pharmacological studies on the role of cholinergic nerves in the neuromuscular transmission in the circular smooth muscle of guinea-pig vas deferens.

Effects of various drugs were examined on the mechanical responses of the circular smooth muscle of guinea-pig vas deferens evoked by field stimulation and ACh. During field stimulation (0.1 msec, 3-80 Hz) a contraction consisting of two (initial and second) phases occurred. In addition, another contraction (after-response) occurred after the cessation of the stimulation particularly at higher frequencies (40-80 Hz). Guanethidine (2-20 microM) suppressed both the initial and second phases of the field stimulation-evoked responses. Prazosin (0.1-1 microM) suppressed the second phase but minimally affected the initial phase. Both phases were suppressed by atropine (0.1-1 microM) and potentiated by physostigmine (5 microM). dTC (0.5-20 microM) did not suppress either phase but potentiated the second phase. ACh (0.28-280 microM) produced a contraction, which was reduced by atropine but was little affected by either dTC or TTX. These results suggest that at the postsynaptic site of the neuromuscular junction in this tissue the sympathetic process activates the smooth muscle through two different types of receptor; one is non-noradrenergic and the other is an alpha-adrenoreceptor. In addition, a cholinergic process also activates the smooth muscle through muscarinic receptors.

Acetylcholine↗
PubMed1986

Evidence for suppression of potassium conductance by noradrenaline in smooth muscle of guinea-pig vas deferens.

The ionic dependency was examined in the reversal potential of the NA-induced membrane depolarization of smooth muscle of the guinea-pig vas deferens, using the double sucrose-gap method. In the control (5.9 mM K) solution and solutions containing 20 and 60 mM K ions, replaced with equimolar amount of Na ions, the reversal potential was negative to the membrane potential at the steady state in each solution, by 19.5, 15.1 and 13.2 mV, respectively. Taking account that the higher external K concentration causes the larger membrane depolarization, these results indicate that the reversal potential shifted toward the positive direction as the external K concentration was increased. On the other hand, the calculated equilibrium potential of K ions in those solutions is -88, -52 and -24 mV, respectively. In those solutions, furthermore, the equilibrium potential of Na ions is 42, 38 and 29 mV, respectively. However, the equilibrium potentials of Ca and Cl ions should be unchanged. Therefore, it is suggested that the reversal potential of the NA-induced depolarization varied in the given different solutions compatibly only with the change in the K equilibrium potential. This provides evidence that in this tissue, NA induces a reduction in the K conductance of the cell membrane.

Animals↗
PubMed1986

Possible relationship between the release of calcium ions and inactivation of the potassium conductance induced by noradrenaline in smooth muscle of the guinea-pig vas deferens.

In order to examine whether any change in cytoplasmic Ca2+ concentration occurs during the noradrenaline (NA)-induced change in the membrane potential, the isometric tension of smooth muscle of the guinea-pig vas deferens was recorded together with membrane potentials using the sucrose-gap method. NA induced a depolarization and an increase in cytoplasmic Ca2+ comprising two (initial and second) phases. In time courses, the depolarization and the second phase of the increase in cytoplasmic Ca2+ were similar. Only at the phase around the onset of the depolarization, the membrane conductance was increased but then, it was decreased. Lowering the external Ca2+ concentration and application of D600 suppressed all of the NA-induced responses. In addition, D600 diminished the size of the NA-induced decrement in the membrane conductance. The present results suggest that the initial phase of the increase in the cytoplasmic Ca2+ is due to the influx of Ca2+ and the second phase, probably to the release of Ca2+ from some intracellular stores. It was discussed that the release of Ca2+ might occur at the internal surface of the membrane, and the membrane might be left less permeable to K+ as a result.

Animals↗