Biomedical subjects

J Nishimura

Publications and source records attributed to J Nishimura.

At least 109 records · Page 6Linked to original sources

PubMed1998

Paroxysmal nocturnal hemoglobinuria: molecular pathogenesis and molecular therapeutic approaches.

Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematologic stem cell disorder classified as an intravascular hemolytic anemia. Abnormal blood cells are deficient in glycosylphosphatidyl inositol (GPI)-anchored proteins. Deficiencies of GPI-anchored complement regulatory proteins, such as decay accelerating factor (DAF) and CD59, render red cells very sensitive to complement and result in complement-mediated hemolysis and hemoglobinuria. In the affected hematopoietic cells from patients with PNH, the first step in biosynthesis of the GPI anchor is defective. Three genes are involved in this reaction step and one of them, an X-linked gene termed PIG-A, is mutated in affected cells. Granulocytes and lymphocytes from the same patient have the same mutation, indicating that a somatic PIG-A mutation occurs in hematopoietic stem cells. The PIG-A gene is mutated in all patients with PNH reported to date. We review these recent advances in the understanding of the molecular pathogenesis of PNH. Furthermore, we present an hypothesis regarding the predominance of the PNH clone, caused by positive selection by hematopoietic suppressive cytokines, such as transforming growth factor (TGF)-beta. In addition, we discuss the possibility of cure for PNH through molecular therapeutic strategy using gene transfer techniques. (Key words: paroxysmal nocturnal hemoglobinuria, glycosylphosphatidylinositol-anchored proteins, PIG-A, clonal dominance, growth advantage, transforming growth factor-beta, gene therapy, molecular therapeutic approach).

Hemoglobinuria, Paroxysmal↗

PubMed1997

Multiple, juxtasutural, cranial hyperostoses and cardiac tumor: a new hamartomatous syndrome?

We report on a Japanese girl with multiple cranial hyperostoses and a cardiac tumor, both of which manifested in early childhood. Unique juxtasutural lesions characterized the cranial findings, including a chain of almost symmetrical osseous protuberances involving the frontozygomatic and frontoparietal junctions, and discrete bony bumps on the right occipitoparietal junction and left temporo-occipital junction. These lesions histologically consisted of thickened mature bone intervened with sparse fibrous tissues, mimicking osteoma. The cardiac mass remained pathologically unknown, but was shown to have fatty elements on magnetic resonance imaging (MRI). The patient showed no evidence of gnathic hyperostoses, ophthalmological abnormalities, skin lesions, or other visceral abnormalities, which ultimately precluded known hamartomatous syndromes with craniofacial hyperostoses, such as Gardner and Proteus syndromes. Yet regional Proteus syndrome could not be completely excluded. The craniofacial deformity as a sequel of hyperostoses in our patient superficially resembled that of X-linked calvarial hyperostosis; however, the vacuolated histiocytes that characterized the hyperostotic lesions were not found in our patient. The present disorder may represent a hitherto unknown hamartomatous syndrome.

Bone Neoplasms↗

PubMed1997

A patient with paroxysmal nocturnal hemoglobinuria bearing four independent PIG-A mutant clones.

Paroxysmal nocturnal hemoglobinuria (PNH) is characterized by clonal blood cells that are deficient in the surface expression of glycosylphosphatidylinositol-anchored proteins due to somatic mutation in the X-linked gene PIG-A. In some patients, more than one abnormal clone may be present. Analysis of bulk DNA/RNA from granulocytes has been useful in identifying the predominant PIG-A mutation in each patient. However, it is often not useful in determining the presence of minor clones. Many patients have cells with partial deficiency. Here, we analyzed the PIG-A gene in two B-cell lines bearing complete or partial deficiencies, cells of hematopoietic progenitor colonies and peripheral blood granulocytes from the same patient. We found that two B-cell lines had different mutations, the granulocytes contained at least two mutants, and the hematopoietic progenitors contained four mutants. Three of the four were shared by B cells and/or granulocytes whereas the other one was found only in the hematopoietic progenitors. The partial deficiency was caused by a point mutation near an alternative splice site within exon 2 that resulted in partial decreases of activity and quantity of the full-length transcript. These results further show the oligoclonal nature of PNH and differences in extent of expansion among mutant clones.

Alternative Splicing↗

PubMed1997

Up-regulation of rho A and rho-kinase mRNAs in the rat myometrium during pregnancy.

It has recently been suggested that rho A and rho kinase (ROK) play a role in the increase in the Ca2+ sensitivity of the smooth muscle myofilaments. In the present study, we investigated the mRNA expressions of rho A and two types of ROK (alpha and beta) in the myometrium obtained from both non-pregnant and pregnant rats. Reverse transcription polymerase chain reaction (RT-PCR) experiments using total RNA from these tissue specimens and the specific primers revealed rho A and both types of ROK mRNAs to be expressed in the rat myometrium. The mRNA expressions of rho A, ROK alpha and ROK beta in the pregnant myometrium were found to increase in comparison to those in the non-pregnant myometrium. These results thus support the idea that the up-regulation of these proteins might be involved in the mechanism underlying the increased contractility of the pregnant myometrium.

Amino Acid Sequence↗

PubMed1997

Down-regulation of endothelin B receptors in autogenous saphenous veins grafted into the arterial circulation.

OBJECTIVES: It has been postulated that endothelin (ET) might be involved in the development of atherosclerotic vascular lesions. The present study was done to characterize changes in the contractility and ET receptor subtypes in the autogenous saphenous vein graft (VG). METHODS: The rabbit saphenous vein (SV) was grafted into the ipsilateral femoral artery (FA), and at 4 weeks after the operation, VG was harvested. In the medial layer samples of SV, VG and FA, the cytosolic Ca2+ concentration ([Ca2+]i) and force were monitored using front-surface fluorometry of fura-PE3, and mRNA expression of ET receptors was evaluated using the reverse transcription polymerase chain reaction. RESULTS: ET-1 (10(-7) M) developed force in SV, VG and FA, to the same extent. Sarafotoxin (S6c; 10(-7) M) developed force in the SV to the same extent as ET-1. However, S6c did not develop force in FA, and slight force developed in VG. Contractions induced by ET-1 were associated with increases in [Ca2+]i. FA expressed ETA receptor mRNA predominantly, and SV expressed both ETA and ETB receptors mRNAs. In VG, the expression of ETB receptor mRNA was markedly reduced, but expression of ETA receptor mRNA remained unchanged. CONCLUSIONS: Functioning ETB receptors and their mRNA are down-regulated when veins are grafted into the arterial circulation. All these changes in gene expression and function are part of adaptive responses known as 'arterialization'.

Animals↗

PubMed1997

T-stem cell leukemia/lymphoma with both myeloid lineage conversion and T-specific delta recombination.

We evaluated retrospectively the clinical and biological characteristics of six patients with CD7+ early T-acute lymphoblastic leukemia and lymphoma (T-ALL/LBL) originating from prothymocyte stage I (pro-T I) or II cells. Patients exhibited mediastinal mass (five of six) and lymphoadenopathy (five of six) but without leukocytosis and circulating blast cells (six of six). All patients achieved a complete remission. All but one had a relapse with a transformation to the mixed type (triphenotype--three cases, biphenotype-two cases) including myeloid features in three patients. The altered phenotypes were myeloperoxidase (MPO)+ (three of five), CD13+ (four of five), CD33+ (three of five) and CD19+ (three of five). The difference for MPO-positivity were observed between the bone marrow (BM)- and lymph node (LN)-blast cells (three of three). On cytogenetic analysis, there is no common abnormality in these patients. Immunomolecular analysis revealed T-cell lineage specific delta gene rearrangements [D delta 2-J delta 1 (five of six) and V delta 1-J delta 1 (one of six)] in all cases. Furthermore, D delta 2-J delta 1 occurred even in the cases with the pro-T I phenotype. Rearrangements of TCR beta, gamma or immunoglobulin heavy chain genes occurred in three patients. The same rearranged band(s) appeared at both diagnosis and relapse, indicating the same originality of the pro-T leukemic cell clone (three of three). We suggest that this type of CD7+ early T-ALL/LBL was transformed from a pro-T I or II cell, such as T-stem cell leukemia/lymphoma, which is a subtype of CD7+ stem cell leukemia as defined by Kurtzberg et al. This study reveals that pro-T I and II cells might be capable of myeloid, T- and B-lymphoid differentiation, and T-cell lineage specific TCR delta recombination occurs.

Adult↗

PubMed1997

Interaction of BCR-ABL with the retinoblastoma protein in Philadelphia chromosome-positive cell lines.

The tyrosine kinase activity of BCR-ABL fusion proteins plays an important role in the pathogenesis of leukemia that is for the Philadelphia chromosome (Ph1). Because nuclear c-ABL is regulated during the cell cycle through a specific interaction with the retinoblastoma protein (pRB), the possible interaction of BCR-ABL with pRB in Ph1-positive cell lines was investigated. P145 c-ABL as well as P190 and P210 BCR-ABL proteins interacted with pRB. Furthermore, c-ABL and BCR-ABL associated with both phosphorylated and nonphosphorylated forms of pRB. These findings suggest that BCR-ABL interferes with pRB function and thereby regulates cell growth.

Animals↗

PubMed1997

The relaxant effect of adrenomedullin on particular smooth muscles despite a general expression of its mRNA in smooth muscle, endothelial and epithelial cells.

1. By use of the reverse transcription polymerase chain reaction (RT-PCR), we determined the expression of adrenomedullin (AM) mRNA in the various tissues of the pig. To evaluate the significance of the expression of AM mRNA, we also determined the effects of AM on the cytosolic Ca2+ concentration ([Ca2+]i) and tension development of the porcine smooth muscle strips obtained from the coronary artery, pulmonary vein, trachea, ileum and urinary bladder. 2.AM mRNA was widely expressed in the porcine tissues examined, which included myocardium (left and right ventricle and right atrium), kidney, lung, endothelial cells (aorta and aortic valve), smooth muscles (aorta, main pulmonary artery, pulmonary vein, renal artery and vein, coronary artery, ileum, trachea and urinary bladder) and epithelial cells (trachea and urinary bladder). 3. AM induced a decrease in [Ca2+]i and tension of the coronary artery, but not the pulmonary vein. AM had no effects on either the [Ca2+]i or tension of the trachea and urinary bladder strips or on the tension development of strips of ileum. 4. These results indicated that AM has a role as an autocrine and/or paracrine regulator of the coronary arterial tone. AM probably does not have an important role in the regulation of the pulmonary venous, tracheal, ileac and urinary bladder smooth muscle tone, even though AM mRNA is expressed in these tissues; the functional significance of AM in these smooth muscles remains to be determined.

Adrenomedullin↗

PubMed1997

Mechanism of contraction induced by bradykinin in the rabbit saphenous vein.

1. By using fura-PE3 fluorometry and receptor-coupled permeabilization by alpha-toxin, the mechanism of the bradykinin (BK)-induced contraction was determined in the rabbit saphenous vein (RSV). The receptor subtype responsible for the BK-induced contraction of RSV was determined by means of a pharmacological blocker study and reverse transcription polymerase chain reaction (RT-PCR). 2. In the presence of extracellular Ca2+ (1.25 mM), BK (10(-11)-3 x 10(-7) M) induced increases in both the cytosolic Ca2+ concentration ([Ca2+]i) and force, in a concentration-dependent manner. Both the release of Ca2+ from the store site and the influx of extracellular Ca2+ contribute to an increase in [Ca2+]i induced by BK. 3. In the absence of extracellular Ca2+, the application of 10(-7) M BK induced transient elevations of [Ca2+]i and force, both of which thereafter declined to the levels observed before the application of BK. When extracellular Ca2+ was replenished (1.25 mM), [Ca2+]i and force increased to form a peak, followed by a sustained elevation in the presence of BK. When an RSV strip was pretreated with 10(-5) M thapsigargin for 20 min, the BK-induced transient increases in both [Ca2+]i and force were markedly inhibited. 4. These responses induced by BK were inhibited by Hoe 140 (D-Arg-[Hyp3, Thi5, D-Tic7, Oic8] bradykinin), a highly specific bradykinin B2 receptor antagonist, in a concentration-dependent manner. In RT-PCR, B2-receptor mRNA was expressed in the smooth muscle of RSV. 5. The [Ca2+]i-force relationships, which were determined by cumulative applications of extracellular Ca2+ (0-5 mM) during 118 mM K(+)-depolarization, shifted to the upper left in the presence of BK, thus indicating that BK induced a greater force than 118 mM K(+)-depolarization for a given level of [Ca2+]i. 6. In alpha-toxin-permeabilized preparations of RSV, application of 10(-7) M BK after a steady state contraction had been induced by a mixture of 5 x 10(-7) M Ca2+, 10(-6) M GTP and 10(-6) M captopril caused an additional force development at a constant [Ca2+]i. However, treatment with 1 mM guanosine-5'-O-(beta-thiodiphosphate) (GDP beta S) for 5 min before and during the application of BK (10(-7) M), abolished this BK-induced additional contraction. 7. These results indicated that in RSV: (1) BK elicits vasoconstriction by increasing the Ca2+ influx from the extracellular space, Ca2+ release from intracellular thapsigargin-sensitive storage sites and increasing the Ca2+ sensitivity of the contractile apparatus, (2) the BK-induced increase in Ca2+ sensitivity is mediated by G-protein, (3) the BK-induced contractions are mediated via B2-receptors and (4) the smooth muscle cells express B2-receptor mRNA.

Animals↗

PubMed1997

The mechanisms of the relaxation induced by vasoactive intestinal peptide in the porcine coronary artery.

1. This study was designed to investigate the mechanism of the relaxation induced by vasoactive intestinal peptide (VIP) in medial strips of the porcine coronary artery, by determining the effect on the cytosolic Ca2+ concentration ([Ca2+]i), the [Ca2+]i-force relation and the involvement of G-protein. 2. Front-surface fluorometry of fura-2 revealed that U46619, a thromboxane A2 analogue, and the high K(+)-depolarization induced increases in both the [Ca2+]i and force of the medial strips. At a steady state of contraction, the extent of an increase in [Ca2+]i induced by 100 nM U46619 was similar to that induced by 30 mM K(+)-depolarization. VIP concentration-dependently (1 nM-1 microM) induced transient decreases in both the [Ca2+]i and force of the medial strips precontracted with 100 nM U46619. The decreases in the [Ca2+]i and force induced by VIP during the contraction with U46619 were much greater than those with 30 mM K(+)-depolarization. 3. The VIP-induced decreases in the [Ca2+]i and force were attenuated by K+ channel blockers such as tetrabutylammonium (TBA: non-selective K+ channel blocker), charybdotoxin (large conductance Ca(2+)-activated K+ channel blocker), and 4-aminopyridine (4-AP: voltage-dependent K+ channel blocker). However, neither glibenclamide (ATP-sensitive K+ channel blocker) nor apamin (small conductance Ca(2+)-activated K+ channel blocker) had any significant inhibitory effect. 4. In the 30 mM K(+)-depolarized strips, pretreatment with thapsigargin, a specific Ca(2+)-ATPase inhibitor of the Ca2+ store sites, completely abolished the VIP-induced decrease in [Ca2+]i, but partially attenuated the VIP-induced decrease in force. 5. VIP shifted the [Ca2+]i-force relation of the U46619-induced contractions to the right in a concentration-dependent manner. In the alpha-toxin-permeabilized strips, VIP decreased the force development at a constant [Ca2+]i level (pCa = 6.5) in a GTP-dependent manner, which was antagonized by guanosine-5'-O-(beta-thiodiphosphate) (GDP beta S). 6. We thus conclude that VIP relaxes the coronary artery via three mechanisms: (1) a decrease in [Ca2+]i by inhibiting the Ca2+ influx presumably through the membrane hyperpolarization mediated by the activation of the large conductance Ca(2+)-activated (charybdotoxin-sensitive) K+ channels and voltage-dependent (4-AP-sensitive) K+ channels; (2) a decrease in [Ca2+]i by sequestrating cytosolic Ca2+ into thapsigargin-sensitive Ca2+ store sites; and (3) a decrease in the Ca(2+)-sensitivity of the contractile apparatus through the activation of G-protein.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗

PubMed1997

Parvovirus B19-associated haemophagocytic syndrome with lymphadenopathy resembling histiocytic necrotizing lymphadenitis (Kikuchi's disease).

A 15-year-old girl developed a haemophagocytic syndrome caused by human parvovirus B19 (PVB19). The cervical lymph node histology, resembling that of histiocytic necrotizing lymphadenitis (HNL, Kikuchi's disease), included several transformed lymphocytes, numerous histocytes, and massive necrosis. We detected PVB19-positive cells in the lymph node by immunohistochemistry. Possible autoimmune mechanisms in HNL-like diseases triggered by PVB19 are discussed.

Adolescent↗

PubMed1997

Resting load and modulation of the myofilament Ca2+ sensitivity in rabbit cerebral arteries.

The effect of preload on myofilament Ca2+ sensitivity was examined using alpha-toxin permeabilization and fura-2 fluorometry in rabbit cerebral arteries. The [Ca2+]i-force curves shifted leftward at a high preload, with a decrease in median effective concentration of Ca2+ in the permeabilized artery. In the fura-2-loaded artery, the preload modulated the force without affecting [Ca2+]i levels during K+ depolarization, and a high preload moved the [Ca2+]i-force curve upward and to the left. It is thus concluded that the preload regulates the Ca2+ sensitivity of the myofilament and, therefore, may play a role in the regulation of cerebral arterial tonus and blood flow.

Actin Cytoskeleton↗

PubMed1997

Expression and function of endothelins, endothelin receptors, and endothelin converting enzyme in the porcine trachea.

Endothelins (ETs) can modulate the airway smooth muscle tone. Using simultaneous measurements of cytosolic Ca2+ concentration ([Ca2+]i) and tension as well as the reverse transcription polymerase chain reaction (RT-PCR), we examined ET systems in the porcine trachea. In the functional study, the application of ET-1, ET-3 or sarafotoxin S6c (S6c) caused increases in [Ca2+]i and tension, in a concentration-dependent manner. These ET ligands were found to increase the Ca2+ sensitivity of the myofilament of the tracheal smooth muscle cells (SMCs). The contractions induced by ET-1 (10(-7) M), an ET receptor (ET-R) non-selective agonist, were much greater than those induced by S6c, an ET(B)-R selective agonist. BQ-123 (10(-6) M), an ET(A)-R antagonist, inhibited the ET-1 induced contraction. These functional experiments suggested the presence of both functioning ET(A)- and ET(B)-Rs in tracheal SMCs. RT-PCR experiments revealed that the tracheal SMCs expressed both ET(A)-R and ET(B)-R mRNAs, while tracheal epithelial cells (EpCs) predominantly expressed ET(A)-R mRNA. The porcine tracheal SMCs and EpCs also expressed pre-pro ET-1 (ppET-1), ppET-3, and endothelin converting enzyme-1 (ECE-1) mRNAs. These results suggested that ETs induce contraction of porcine tracheal SMCs not only by increasing [Ca2+]i but also increasing the Ca2+ sensitivity of the myofilament and that ETs could potentially be the autocrine and/or paracrine transmitters to regulate the contraction in the porcine airway smooth muscle.

Animals↗

PubMed1997

Effects of noradrenaline on GnRH-secreting immortalized hypothalamic (GT1-7) neurons.

Noradrenaline (NA) is one of the most important neurotransmitters involved in the regulation of gonadotropin-releasing hormone (GnRH) secretion. In this study, the effects of NA on GnRH secretion, intracellular Ca2+ concentrations ([Ca2+]i), and membrane potentials were investigated in immortalized hypothalamic neurons (GT1-7) to determine the direct effects of NA on GnRH cells. Cells were perfused in a plastic minicolumn, and GnRH concentrations of the effluents were measured. NA increased the release of GnRH in a dose-dependent manner. Cells were loaded with a 4 microM Fura 2-AM, and the ratio of the intensities of fluorescent emission at 510 nm with excitation at 340 and 380 nm was calculated at 100-ms intervals. NA increased the [Ca2+]i responses of single GnRH cells dose-dependently. The NA-induced [Ca2+]i increase was attenuated in the absence of extracellular calcium and was blocked by the beta-adrenergic antagonist propranolol, but not by the alpha-adrenergic antagonist phentolamine. The cell membrane potential was recorded with a whole-cell patch clamp amplifier with glass-electrodes. NA induced membrane depolarization under current-clamp conditions. The depolarization was also inhibited by propranolol, but not by phentolamine. The results show that NA directly affects the membrane potential of GT1-7 cells via beta-adrenergic receptors and induces Ca2+ mobilization; these effects stimulate GnRH secretion.

Adrenergic alpha-Agonists↗

PubMed1997

Biphenotypic blast crisis of chronic myelogenous leukemia: abnormalities of p53 and retinoblastoma genes.

The molecular mechanisms responsible for progression of chronic myelogenous leukemia (CML) to blast crisis have not been well defined. Blast crisis may be partially related to inactivation of tumor suppressor genes/such as p53 or retinoblastoma (Rb) gene. There is evidence for an association of blast cell phenotypes in CML with alterations of these genes: a strong association of myeloid phenotypes with abnormalities of the p53 gene and a weaker association of lymphoid phenotypes with abnormalities of the Rb system. We found a marked decrease in Rb gene product and rearrangements of the p53 gene simultaneously in two cases of biphenotypic blast crisis of CML (myeloid and B-lymphoid). These results support the association of blast cell phenotypes with alterations in tumor suppressor genes in CML blast crisis.

Blast Crisis↗

PubMed1997

Comparative studies of CAM 123-6 and carcinoembryonic antigen for the serological detection of pulmonary adenocarcinoma.

Carcinoembryonic antigen (CEA) has been clinically used as a serum marker for lung cancer, especially for pulmonary adenocarcinoma. Since we had developed a tumor marker against pulmonary adenocarcinoma, CAM 123-6 belonging to KL-6 MUC 1 mucin, we compared its clinical value with that of CEA, in combination with squamous cell carcinoma-related antigen (SCC) and neuron-specific enolase (NSE). The subjects were 30 patients with adenocarcinoma, 23 with squamous cell carcinoma, 16 with small cell carcinoma, and 20 with benign lung disease. For discriminating lung cancer from benign lung disease, the combination of CAM 123-6, SCC, and NSE showed 64% diagnostic accuracy, and the combination of CEA, SCC, and NSE 65%. In differentiating pulmonary adenocarcinoma from other lung cancer, the diagnostic accuracy of CAM 123-6 was 81% and that of CEA was 74%, although there was no significant difference between them. These observations indicate that the diagnostic accuracy of CAM 123-6 is similar to that of CEA. Neither marker is sufficiently specific to differentiate pulmonary adenocarcinoma from other forms of lung cancer.

Adenocarcinoma↗

PubMed1997

Chronic exertional compartment syndrome in lower legs: localization and follow-up with thallium-201 SPECT imaging.

UNLABELLED: The purpose of this study was to ascertain whether 201Tl SPECT imaging of the leg is useful in precise localization of the ischemic compartment involved in chronic exertional compartment syndrome (CECS). METHODS: Imaging and quantitative analyses of postexercise 201Tl SPECT leg examinations were retrospectively performed in nine patients with clinically diagnosed CECS and eight control subjects. Imaging and quantitative criteria for the ischemic compartment were decreased 201Tl perfusion less than the lower limits of normal, which were defined as 2 s.d. below the mean percentage uptake of the control subjects. The SPECT imaging results were compared with those of quantitative analysis, postoperative SPECT images and clinical diagnoses. RESULTS: Postexercise normal legs had nonuniform 201Tl distribution in both legs and in the four compartments. Lower limits of normal mean percentage 201Tl uptake were about 60% for the anterior compartment and about 50% for the other three compartments. Redistribution was observed in 67% of normal compartments in the control subjects. The SPECT images demonstrated 16 ischemic compartments in eight of the nine patients. The SPECT results were consistent with those of quantitative analysis. There were discrepancies between the clinical and SPECT diagnoses in six legs (33% of the 18 legs) of five patients. Postoperative SPECT demonstrated 201Tl perfusion was improved in all involved compartments for that fasciotomy was performed. CONCLUSION: Thallium-201 SPECT imaging of the legs can easily provide precise localization of the ischemic compartment, which is demonstrated as decreased 201Tl distribution on the stress image. This technique is promising for the screening and follow-up of CECS.

Adult↗

PubMed1997

Diadenosine polyphosphates directly relax porcine coronary arterial smooth muscle.

By use of front-surface fluorometry and fura-2-loaded medial strips of the porcine coronary artery, cytosolic Ca++ concentration ([Ca++]i) and force development were monitored simultaneously to determine the mechanisms of vasorelaxation induced by the diadenosine polyphosphates (APnA) diadenosine 5',5'''-P1, P4-tetraphosphate (AP4A) and diadenosine 5',5'''-P1,P5-pentaphosphate (AP5A). APnA concentration-dependently inhibited the sustained elevations of [Ca++]i and force induced by U-46619, a thromboxane A2 analog, in the presence of extracellular Ca++. APnA shifted the [Ca++]i-force relation curves of contractions induced by various concentrations of high K+ to the right. The AP4A-induced decreases in [Ca++]i and force were largely attenuated by tetrabutylammonium. The AP4A-induced decreases in force were attenuated by 4-aminopyridine and charybdotoxin. The AP5A-induced decreases in [Ca++]i and force were attenuated by tetrabutylammonium, 4-aminopyridine and charybdotoxin. In the absence of extracellular Ca++, APnA did not inhibit the transient elevations of [Ca++]i induced by histamine or caffeine. Both AP4A and AP5A increased intracellular cAMP content. We thus conclude that AP4A and AP5A relax the porcine coronary artery by decreasing [Ca++]i, possibly through the activation of K+ channels, but not through inhibition of intracellular Ca++ release and by decreasing the Ca++ sensitivity of the contractile machinery. These effects were considered to be mediated by cAMP.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗