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Mikio Marumo

Publications and source records attributed to Mikio Marumo.

8 recordsLinked to original sources
PubMed2006

TRPC4 expression determines sensitivity of the platelet-type capacitative Ca2+ entry channel to intracellular alkalosis.

The present study was designed to analyze the molecular basis of the intracellular pH-dependent capacitative Ca2+ entry (CCE) of human platelets and megakaryocytic cells, specifically to test the hypothesis that members of the classical transient receptor potential (TRPC) protein family are involved in the CCE pathway that is promoted by intracellular alkalosis. Human platelets as well as the tested megakaryocytic cell lines (CMK cells, MEG-01 cells) and HEK293 cells displayed thapsigargin-induced CCE and responded to monensin with comparable elevation in intracellular pH. Promotion of CCE by monensin-induced intracellular alkalosis, however, was profound in mature platelets, moderate in CMK cells and lacking in MEG-01 cells as well as in HEK293 cells. Analysis of the TRPC expression pattern by immunoblotting revealed that mature platelets and CMK cells express TRPC4 along with TRPC1 and TRPC3, while TRPC4 is lacking in MEG-01 cells. HEK293 cells displayed CCE characteristics as well as lack of TRPC4 expression similar to MEG-01 cells. Over-expression of TRPC4 in HEK293 cells was found to result in a gain of pH-sensitivity of CCE with clearly detectable promotion of CCE in response to monensin. These results suggest that platelet CCE channel complexes contain TRPC4 as a molecular component that determines sensitivity of CCE to intracellular alkalosis.

Alkalosis↗
PubMed2005

Monensin augments capacitative Ca2+ entry and subsequent aggregation of platelets via an intracellular alkalosis-mediated mechanism.

Effects of monensin, an ionophore that facilitates the transmembrane exchange of Na+ for H+, on capacitative Ca2+ entry (CCE) of platelets were investigated. CCE of human platelets was induced by addition of Ca2+ to a nominally Ca2+-free medium after release of intracellular stored Ca2+ caused by thapsigargin. CCE was strongly inhibited by SKF-96365 (1-[beta-(3-[4-methoxyphenyl]propoxy)-4-methoxyphenethyl]-1H-imidazole hydrochloride). Monensin significantly increased SKF-96365-sensitive CCE and subsequent platelet aggregation. Monensin also induced a sustained increase in intracellular pH. The augmenting effect of monensin on CCE and subsequent platelet aggregation was not observed in the presence of sodium propionate, which canceled intracellular alkalinization induced by monensin. These results suggest that monensin augments CCE of platelets by a mechanism mediated by intracellular alkalosis.

Alkalosis↗
PubMed2005

[Effects of ethanol ingestion on glucose tolerance in people with different genotypes of ALDH2].

Effects of alcohol drinking on glucose tolerance were investigated in male healthy subjects (20-36 years old) with different phenotypes of aldehyde dehydrogenase 2 (ALDH2). Oral glucose tolerance test was performed in each subject twice with and without simultaneous oral ingestion of ethanol. Simultaneous oral ingestion of ethanol (10 g) significantly enhanced the early increase in plasma insulin concentration at 30 min after ingestion of glucose (100 g) in subjects with normal ALDH2 phenotype, while the increase in early insulin response due to alcohol was slight and not significant in those with atypical ALDH2. On the other hand, the early increase in plasma glucose concentration at 30 min after glucose inges-tion was not affected by simultaneous ethanol drinking in both groups of subjects with normal and atypical ALDH2 phenotypes. Thus, drinking alcohol together with a simple sugar causes enhancement of early insulin response, which is more prominent in people with normal ALDH2 phenotype than in those with atypical ALDH2 phenotype.

Adult↗
PubMed2003

Diverse effects of monensin on capacitative Ca2+ entry and release of stored Ca2+ in vascular smooth muscle cells.

The effects of monensin, an activator of Na(+)/H(+) exchanger (NHE), on capacitative Ca(2+) entry (CCE) were investigated using A7r5 cells. Capacitative Ca(2+) entry was induced by elevation of extracellular Ca(2+) concentrations of A7r5 cells in which stored Ca(2+) had been depleted by previous administration of thapsigargin. Capacitative Ca(2+) entry was abolished by pretreatment of the cells with SKF-96365 (1-[beta-(3-[4-methoxyphenyl]propoxy)-4-methoxyphenethyl]-1H-imidazole hydrochloride) but was not affected by pretreatment with verapamil. Monensin significantly increased capacitative Ca(2+) entry. On the other hand, 5-hydroxytryptamine-induced inositol monophosphate accumulation and subsequent intracellular Ca(2+) release from its stores were significantly inhibited by monensin, while thapsigargin-induced Ca(2+) release was not affected by monensin. These results suggest that monensin has diverse actions on capacitative Ca(2+) entry and agonist-induced release of stored Ca(2+) in vascular smooth muscle cells.

Animals↗
PubMed2003

Intracellular alkalinization augments capacitative Ca2+ entry in vascular smooth muscle cells.

Agonist-induced Ca2+ influx of vascular smooth muscle cells is thought to be triggered by depletion of intracellular Ca2+ stores. This study investigated the effects of intracellular alkalinization on capacitative Ca2+ entry in A7r5 rat aortic smooth muscle cells. Intracellular alkalinization was induced by NH(4)Cl. Transplasmalemmal Ca2+ influx due to Ca2+ store depletion induced by thapsigargin, which was abolished by pretreatment of the cells with SKF-96365 but not affected by that with verapamil, was significantly increased by pretreatment with NH(4)Cl. Neither 5-hydroxytryptamine-induced inositol monophosphate accumulation nor intracellular Ca2+ release from its stores was affected by NH(4)Cl. These results suggest that intracellular alkalinization acts on the process(es) after depletion of Ca2+ stores and facilitates capacitative Ca2+ entry in vascular smooth muscle cells.

Ammonium Chloride↗
PubMed2003

Intracellular alkalinization augments capacitative Ca2+ entry in platelets.

In order to elucidate the significance of intracellular alkalinization in signal transduction of platelets, we investigated the effects on capacitative Ca(2+) entry (CCE) of intracellular alkalinization that was induced by NH(4)Cl. Addition of NH(4)Cl (10 mM) to the medium resulted in an elevation of intracellular pH by about 0.35, which was eliminated by simultaneous addition of propionate (20 mM), an inducer of intracellular acidification, to the medium. CCE was induced by an extracellular addition of Ca(2+) to platelets in which Ca(2+) stores had been depleted by stimulation with thapsigargin in nominally Ca(2+)-free medium. NH(4)Cl markedly augmented CCE and subsequent platelet aggregation, both of which were abolished in the presence of SKF-96365, an inhibitor of capacitative Ca(2+) entry in non-excitable cells such as platelets. The augmentation of CCE and subsequent aggregation by NH(4)Cl was not observed in the presence of propionate or SKF-96365. Extracellular alkalosis induced by Tris also markedly augmented CCE and subsequent aggregation. These augmenting effects of extracellular alkalosis by Tris were significantly but incompletely inhibited by simultaneous addition of propionate (20 mM), which completely eliminated elevation of intracellular pH elicited by Tris. Thus, the augmenting effect of extracellular alkalosis on CCE was in part mediated by intracellular alkalosis. These findings suggest that intracellular alkalinization is a potent signal that augments CCE in platelets.

Alkalosis↗
PubMed2002

Intracellular alkalinization augments platelet aggregation due to increase in cytosolic free-Ca2+.

Intracellular pH is known to increase during agonist-induced platelet activation. In order to elucidate the role of intracellular alkalinization in platelet activation, the effects of NH4Cl, as a tool to induce intracellular alkalinization, on ionomycin-induced platelet activation were investigated. NH4Cl (2.5-10 mM) concentration-dependently induced intracellular alkalinization. Platelet aggregation induced by ionomycin (0.1 microM) was augmented by treatment with NH4Cl (2.5-10 mM). Ionomycin-induced platelet aggregation in the absence of extraplatelet Ca2+, which was markedly attenuated compared to that in the presence of extraplatelet Ca2+, was also augmented by NH4Cl. NH4Cl treatment increased the number of large aggregates after ionomycin stimulation, while it decreased the number of small aggregates. Both transplasmalemmal Ca2+ entry and intracellular Ca2+ release induced by ionomycin were increased by treatment with NH4Cl (10 mM). SKF-96365 (100 microM), an inhibitor of receptor-operated Ca2+ channels, did not affect ionomycin-induced Ca2+ entry but abolished the effect of NH4Cl on Ca2+ entry. Thus, NH4Cl augments receptor-operated Ca2+ channels and intracellular Ca2+ release. These findings suggest that intracellular alkalinization plays a significant role in agonist-induced platelet activation.

Ammonium Chloride↗