The inner sublayer of the circular muscle coat in the canine proximal colon: origins of spontaneous electrical and mechanical activity

In the canine proximal colon, tissue near the submucosal surface of the circular muscle layer produces spontaneous mechanical contractions, synchronized with electrical slow waves. Comparative physiological examination of tissue strips from various regions of the submucosa and circular muscle coat revealed that the characteristic smooth muscle tissue of the innermost sublayer of the circular muscle is required for this rhythmical phenomenon. Histological examination showed that tissues containing special smooth muscle cells form an inner sublayer of the circular muscle coat. These innermost muscle cells were distinguishable from the bulk circular muscle cells by the following features: 1) flattened and shorter shapes of the cell and nucleus, 2) numerous caveolae on the cell surface, 3) abundant mitochondria, and 4) frequent gap-junction formations. Neither slow waves nor spontaneous mechanical rhythmicities were recorded from the submucosal connective tissue or from the bulk circular muscle tissue without the inner sublayer. The thicker smooth muscle cells found in the submucosal border specimens were identical in histological features to the bulk circular muscles which produced no slow waves and no spontaneous contractions. Cellular elements in the interstitium, such as fibroblasts, mast cells and macrophages, were found in all tissue strips that were physiologically examined. Nerve elements were found in all the specimens; however, there was a unique nerve network probably corresponding to the plexus entericus (submucosus) extremus described by Stach (1972). It was concluded, therefore, that the inner sublayer characterized by special smooth muscle cells with a delicate nerve plexus is essential for producing spontaneous activities of the circular muscle coat in the canine proximal colon.

Allele-specific PCR reveals that CYP6D1 is on chromosome 1 in the house fly, Musca domestica

A cytochrome P450, termed P450lpr, is the major P450 responsible for pyrethroid resistance in the Learn-PyR (LPR) strain of house fly. Recently, the putative gene (CYP6D1) coding for P450lpr has been sequenced from the LPR and aabys strains of house fly. Allele-specific polymerase chain reaction (ASPCR) was used for linkage group analysis with backcross progeny from the wild type LPR strain and a multiple marker strain (aabys). We found that CYP6D1 is linked to chromosome 1. The possible role of regulatory or modifying genes responsible for elevated P450lpr expression is discussed in relation to the chromosomal linkage of CYP6D1.

[A case of atypical course after balloon occlusion for high flow traumatic carotid-cavernous fistula]

We treated a patient with a high flow traumatic carotid-cavernous fistula (CCF) by transarterial balloon occlusion. A 26-year-old male sustained an injury of the head. After 2 months he was admitted to our hospital due to exophthalmos, congestion of the palpebral conjunctiva. Right common carotid angiography showed a CCF with high flow shunt. He was treated by the endovascular balloon technique. Following the operation, abducens nerve palsy, headache, vomiting and convulsion developed and disappeared gradually within one week. Post operative 123I-IMP-SPECT revealed hyperperfusion of cerebral circulation compared to preoperative one. Post operative rt-carotid angiography showed pseudoaneurysm at cavernous portion of internal carotid artery. We discussed on abducent nerve palsy, pseudoaneurysm and hyperperfusion syndrome.

Effects of gabexate, a protease inhibitor, on smooth muscle of guinea-pig stomach fundus

A protease inhibitor, gabexate (ethyl-p-6-guanidinohexanoyloxy benzoate), was found to have an antimuscarinic action in muscle strips of the guinea-pig gastric fundus. Gabexate reversibly inhibited carbachol-induced contractions in the presence of prostaglandin synthesis inhibitors (indomethacin or meclofenamate) with a pA2 of 5.66 for the circular and 5.25 for the longitudinal muscle. The effect was not affected by tetrodotoxin. Gabexate also inhibited contractions produced by prostaglandin E2 (PGE2) (21.7 +/- 7.3% with 30 microM, n = 12). The inhibition was markedly potentiated by anticholinesterase, diisopropyl fluorophosphate, but converted to contraction by atropine. In the absence of PGE2, gabexate produced no mechanical response on its own even after atropine application. Treatment with hemicholinium, an acetylcholine synthesis inhibitor, also converted the relaxant effect of gabexate, applied during PGE2-induced contraction, to contraction. Gabexate also inhibited contracture induced by 30 mM K+ weakly (13 +/- 2% with 30 microM, n = 5). This relaxation was abolished by atropine, without converting to contraction. PGE2 and excess K+ are likely to release acetylcholine from nerve fibres. These results suggest that the inhibitory effect of gabexate is mainly due to the muscarinic receptor blocking action. In addition, gabexate has a potentiating action on the prostaglandin-induced contraction.

cDNA and deduced protein sequence of CYP6D1: the putative gene for a cytochrome P450 responsible for pyrethroid resistance in house fly

A microsomal cytochrome P450 from the house fly (Musca domestica), termed P450lpr, is involved in P450 monooxygenase-mediated pyrethroid resistance and is expressed at 8-fold higher levels in the insecticide resistant LPR strain compared to a susceptible strain. An internal cDNA sequence was amplified by polymerase chain reaction (PCR) using degenerate primers based on known P450lpr polypeptide sequences, and the remainder of the sequence was amplified by single side-specific PCR. A 1.8 kb cDNA sequence was obtained from 3 overlapping PCR products, with an open reading frame encoding a P450 protein of 516 residues (M(r) 59,182). This gene has been designated CYP6D1 within the P450 gene superfamily. CYP6D1 exhibits most similarity (28.2-29.8% positional identity) to butterfly CYP6B1, house fly CYP6A1 and Drosophila CYP6A2, and also exhibits comparable similarity (24.7% identity) to rat CYP3A1. The deduced protein sequence contains a hydrophobic N-terminal region and conserved sequences thought to be involved in heme-binding and electron donor-protein interactions. Comparison of CYP6D1 with its four most similar proteins (CYP6B1, CYP6A1, CYP6A2 and CYP3A1) reveals the presence of extensive stretches of residues in an alignment row in 2 possible substrate-binding regions. Three introns of 74, 66 and 64 bp, having 5'-GT and AG-3' ends, split the CYP6D1 coding region in genomic DNA. Results indicate that CYP6D1 is likely the P450lpr gene.

The regulation of cholesteryl ester metabolism by 17 beta-estradiol in macrophages. Activation of neutral cholesterol esterase

The mechanism for antiatherogenic effects of 17 beta-estradiol (E2) was investigated in J774 A.1 cells incubated with beta-VLDL. E2 at physiological concentrations (0.25 and 2.5 nM) inhibited an accumulation of cellular cholesteryl esters and enhanced their hydrolysis in foam cells. These phenomena were preceded by activation of neutral cholesterol esterase through an increase in cyclic AMP-dependent protein kinase activity. 17 alpha-estradiol, progesterone, and testosterone lacked such stimulatory effects on neutral cholesteryl esterase.

Effects of various natural antioxidants on the Cu(2+)-mediated oxidative modification of low density lipoprotein

We have reported in our previous paper that several flavan-3-ol derivatives (tea polyphenols) inhibited the Cu(2+)-mediated low density lipoprotein (LDL) oxidation in vitro. (-)-Epigallocatechin gallate (EGCG), in particular, exhibited strong inhibition. In this study, we have compared the antioxidative effects of EGCG with those of other natural antioxidants, such as flavonols, sesaminol, curcuminoid derivatives, tocopherol analogues and theaflavins. The antioxidative effects were monitored by conjugated diene formation in LDL which was carried out at 37 degrees C with 5 microM CuSO4 with or without antioxidants. Dibutyl hydroxytoluene (BHT) was used as a reference compound. The lag-time before the onset of conjugated diene formation was more than 100 min in the presence of 0.5 microM EGCG, theaflavin, myricetin, quercetin, and sesaminol. The ability to prolong the lag-time was in the order of sesaminol > quercetin > EGCG > theaflavin > or = myricetin > BHT > alpha-tocopherol. Among the 4 tocopherol analogues used, alpha-tocopherol showed the strongest antioxidative activity. We have also studied the effects of EGCG, BHT, and alpha-tocopherol on cholesteryl and alpha-tocopherol on cholesteryl ester (CE) degradation and apolipoprotein B 100 (apo B 100) fragmentation in the Cu(2+)-mediated oxidative modification of LDL. EGCG was the most effective inhibitor of CE degradation and apo B 100 fragmentation.

Multidrug resistance gene expression in childhood medulloblastoma: correlation with clinical outcome and DNA ploidy in 29 patients

Twenty-nine children treated for medulloblastoma between 1987 and 1991 were reviewed. Thirteen patients with high-risk medulloblastoma characterized by incomplete resection, diploid tumor or subarachnoid dissemination received chemotherapy following radiation therapy. Three received postoperative chemotherapy. Eight patients who had been treated with postoperative radiation therapy also received chemotherapy for recurrent tumors. After a minimum 3-year follow-up period, 16 were alive but 13 had died from recurrent tumors. In order to evaluate the possible participation of P-glycoprotein (Pgp)-mediated multidrug resistance (MDR) in medulloblastoma therapy and its correlation with prognosis, archival specimens were examined by immuno-histochemistry utilizing 3 monoclonal antibodies against Pgp and 6 cases by reverse-transcriptase polymerase chain reaction (RT-PCR) using MDR1-specific primers. Sixteen patients (55%) had MDR expression detected either by 1 of the 3 antibodies or by RT-PCR. DNA ploidy study was also performed on 18 specimens. We correlated patients' outcome with variable factors (extent of surgical resection, chemotherapy, DNA ploidy) and MDR expression. Patients who were treated with radiation therapy and adjuvant chemotherapy had a significantly better (p = 0.036) survival than those with radiation therapy alone, despite the fact that the former group of patients was considered to be high-risk. The extent of surgical resection and DNA ploidy did not correlate with prognosis. However, a statistically significant association was found between MDR expression and outcome (p = 0.007). Among the patients who received chemotherapy, positive MDR expression significantly correlated with poor outcome (p = 0.036). Our results showed that Pgp-mediated intrinsic MDR in medulloblastomas seems to correlate with an adverse outcome. This information may be used in designing new therapeutic protocols for medulloblastoma.

The relationship between the expression of proliferating cell nuclear antigen and clinicopathological variables of gastric-cancer

A monoclonal antibody against proliferating cell nuclear antigen (PCNA), PC10, was applied to 96 gastrectomy specimens obtained from patients with gastric cancer. Resected tissue was routinely processed and stained immunohistochemically with PC10. One thousand tumor cells were counted and the ratio of the number of stained cells to total tumor cells was calculated as the PCNA index, which ranged from 13.8% to 88.8% with a mean of 61.4%. Although the PCNA index did not correlate with pathological variables including histological type, lymph node metastasis, growth pattern and venous invasion, it was significantly lower in mucosal carcinomas compared with submucosal and advanced carcinomas.

[Response of individual abdominal muscles to nasal CPAP in supine and standing positions in humans]

The respiratory function of individual abdominal muscles in humans is not well known. Some workers have reported that abdominal muscles act as a single unit during breathing, whereas others have reported differential activation. In the present study, fine wire electrodes were inserted into the rectus abdominis (RA), external oblique (EO), internal oblique (IO), and transversus abdominis (TA) muscles in six healthy awake subjects under direct vision provided by high-resolution ultrasonography. Electromyographic (EMG) signals were then recorded in the supine and standing positions during resting ventilation without nasal continuous positive airway pressure (nCPAP), then on nCPAP at 5, 10, 15, and 20 cmH2O. Peak values of integrated EMG during expiration were measured. For each abdominal muscle, the number of subjects showing expiratory EMG activity increased with increasing nCPAP or with a change in posture from supine to standing or both. The number of subjects showing expiratory abdominal muscle activity under any condition followed the order: RA < or = EO < or = IO < or = TA. Peak expiratory EMG activity increased significantly with increasing nCPAP in the standing position for EO (p < 0.05), and in both positions for IO and TA (both p < 0.01). These results suggest that: 1) both the standing position and nCPAP imposed an expiratory load, 2) TA and IO are most sensitive to expiratory loading, and are the primary expiratory muscles, and 3) RA is least sensitive to expiratory loading, and is a secondary expiratory muscle. We conclude that individual abdominal muscles respond differently to expiratory loading.

Phosphomonoesters in the guinea-pig taenia caeci: pH-dependency of the phosphomonoester peaks in 31P-NMR

In the smooth muscle of guinea-pig taenia caeci, unlike cardiac and skeletal muscles, two prominent peaks are constantly observed in the phosphomonoester (PME) region (at 6.8 and 6.3 ppm) of 31P-NMR spectra. Tissue extracts, whose pH were adjusted to the intracellular pH of 7.1, also showed such peaks. According to the pH-dependency of the chemical shifts of known PMEs, these peaks were identified as phosphorylethanolamine (PEt) and phosphorylcholine (PCh), the intermediary metabolites of membrane phospholipid turnover. In normal solution, the intracellular pH (pH(i)) which was estimated from the chemical shifts of PMEs (PEt 7.07; PCh 7.17) agreed with that from P(i) (7.10). When preparations were exposed to hypoxia and high-Mg2+ conditions, a reasonable correlation was found between estimations of pH(i) from the PME and P(i) peaks. The chemical shifts of these PME peaks may be used for estimation of pH(i), at least, when there is a need to know relative changes of pH(i), as a complementary purpose, and also whenever the P(i) peak is not clearly observed.

Mechanism of the cytolytic action of Pseudomonas aeruginosa cytotoxin: oligomerization of the cytotoxin on target membranes

Pseudomonas aeruginosa cytotoxin (CTX) is thought to be a pore-forming polypeptide of 29 kDa. To study whether CTX assembles into oligomer on target membranes, we solubilized membrane-bound toxin with 1% sodium dodecyl sulfate (SDS) at 25 degrees C and analyzed its molecular size using SDS-polyacrylamide gel electrophoresis and immunoblot analysis. The results indicate that CTX forms a complex of approximately 145 kDa on the surface of erythrocytes and lipid vesicles, and that the complex formation is closely correlated with the toxin-induced permeabilization of target membranes. Thus, CTX may assemble into a pore-forming oligomer on target membranes.

[A case of adult respiratory distress syndrome treated with 5 ppm nitric oxide inhalation]

A cases of adult respiratory distress syndrome, ARDS, was treated with nitric oxide (NO) inhalation for 10 days. The optimal dose of inhaled NO was determined by the dose-response relationship with NO concentration ranging from 5 to 160 ppm. 5 ppm of NO inhalation considerably increased PaO2 and decreased mean pulmonary arterial pressure (mPAP). Further increase in concentration of inhaled NO did not result in remarkable change in PaO2, but decreased mPAP. NO inhalation therapy was begun with 20 ppm of NO and 0.95 of FIO2, and on the 6th day NO concentration was decreased to 5 ppm with 0.7 of FIO2. In this case of ARDS, FIO2 could be sufficiently decreased and PaO2 maintained at more than 60 Torr with 5 ppm NO inhalation.

The inhibitory effects of tea polyphenols (flavan-3-ol derivatives) on Cu2+ mediated oxidative modification of low density lipoprotein

Tea polyphenols (flavan-3-ol derivatives) suppressed the oxidative modification of low density lipoprotein (LDL) which is assumed to be an important step in the pathogenesis of atherosclerosis lesions. Inhibitory experiments on the oxidative impairment of porcine serum LDL by flavan-3-ols were carried out by incubating them at 37 degrees C in the presence of 5 microM Cu2+. The oxidation of LDL was monitored either by an absorption increase at 234 nm due to the conjugated diene formation, or the formation of hydroperoxides and thiobarbituric acid reactive substances (TBARS). It was found that the oxidation was strongly inhibited by various flavan-3-ols, and a lag time over 100 min appeared, depending on the types of flavan-3-ols used. The activities based on the prolongation of the lag time were in the order of (-)-epigallocatechin (EGC) < (+)-catechin (C) < (-)-epicatechin (EC) < (-)-epicatechingallate (ECG) < (-)-epigallocatechingallate (EGCG). IC50 of flavan-3-ols on Cu2+ mediated hydroperoxides and TBARS formation of LDL were 0.90, 0.95 microM for ECG and 2.38, 2.74 microM for EGC, respectively. It was found that the Cu2+ mediated cholesterol ester degradation in LDL was almost completely inhibited by 5.0 microM C or EGCG. Cu2+ mediated apolipoprotein B-100 fragmentation was also inhibited (up to 60%) in the presence of C or EGCG.

A murine nephritogenic monoclonal antibody binds to both single-stranded deoxyribonucleic acid and glomerulus

BACKGROUND

Autoantibodies such as anti-DNA and antimyeloperoxidase (MPO) antibodies have been shown to cause glomerulonephritis in experimental animal models. To analyze pathogenic autoantibodies, we developed hybridomas from spleen cells of nontreated FGS mice, in which focal segmental glomerular sclerosis develops spontaneously.

EXPERIMENTAL DESIGN

Reactivity and specificity of a monoclonal antibody (FG1H5) were examined using enzyme-linked immunosorbent assay and cryosections of mouse organs as substrates. Immunoprecipitation was performed to analyze reactive antigens. Hybridoma cells were injected ip into severe combined immunodeficiency (SCID) mice to examine their nephritogenicity in vivo.

RESULTS

The binding of FG1H5 to single-stranded DNA (ssDNA) was inhibited by ssDNA and also MPO. The binding of FG1H5 to MPO was weak, not inhibited by MPO, and markedly enhanced by the presence of ssDNA. This marked enhancement of the binding to MPO was abolished by DNase I-treatment of the mixture of FG1H5 and ssDNA. When MPO was introduced into ssDNA-coated wells, the binding of FG1H5 to ssDNA was inhibited. On the other hand, when ssDNA was introduced into MPO-coated wells, the binding of FG1H5 to MPO was markedly enhanced. Inhibition tests using double-stranded DNA revealed that FG1H5 is specific for ssDNA. Histologic examination of FG1H5-reactive antigen using SCID mouse kidney showed positive stainings in the nucleus and glomerulus (mainly the mesangium). These positive stainings were abolished after the incubation of FG1H5 with ssDNA. The DNase I treatment of kidney sections markedly reduced the nuclear staining, but the staining of the glomerulus was preserved. Immunoprecipitation of a soluble fraction of SCID mouse kidney with FG1H5 revealed that FG1H5-reactive antigen in the glomerulus is an approximately 28-kilodalton molecule. When FG1H5 hybridoma cells were injected ip into SCID mice, the mice showed glomerulonephritis with the increases in mesangial cells and matrix as well as immunoglobulin M deposition mainly in the mesangium.

CONCLUSIONS

Data demonstrate that FG1H5 binds strongly and specifically to ssDNA (but weakly and nonspecifically to MPO), and that ssDNA and MPO bind to each other. One monoclonal antibody reacts with both the nucleus and glomerulus (mainly the mesangium), and glomerular staining is not caused by nonspecific DNA binding. FG1H5, which binds to ssDNA, can induce glomerulonephritis, probably because of a direct crossreactivity to glomerular components.

[Effect of nasal CPAP on human diaphragm position and lung volume]

The cephalic margin of the zone of apposition (ZOA) was observed with ultrasonography at ambient pressure and during nasal continuous positive airway pressure (nasal CPAP) in nine awake healthy males in a supine position. In a relaxed state at ambient pressure, there was a significant (p < 0.001) linear relationship between lung volume and the movement of the cephalic margin of the ZOA over the range from maximum expiratory position (MEP) to maximum inspiratory position (MIP). With nasal CPAP, functional residual capacity increased significantly (p < 0.01) in proportion to the increase in CPAP. At 20 cmH2O CPAP, the mean increase in volume at end expiration was 36% of the vital capacity measured at ambient pressure. The cephalic margin of the ZOA moved significantly (p < 0.01) in a caudal direction as CPAP was increased. At 20 cmH2O CPAP, the cephalic margin of the ZOA at end expiratory position (EEP) had moved 55% of the difference from MIP to MEP measured at ambient pressure. The end expiratory diaphragm position during nasal CPAP was lower than the diaphragm position at ambient pressure when lung volumes were equal. These results suggest that during nasal CPAP the chest wall is distorted from its relaxed configuration, with a decrease in rib cage expansion and an increase in outward displacement of the abdominal wall.

Enhancement of endothelium-dependent relaxation in the aorta from stroke-prone spontaneously hypertensive rats at developmental stages of hypertension

1. Endothelium-dependent relaxation (EDR) in aortic rings from young (8 weeks) and adult (16 weeks and 20 weeks) stroke-prone spontaneously hypertensive rats (SHRSP) was investigated in comparison with age-matched Wistar-Kyoto rats (WKY). 2. At 8 weeks, acetylcholine (3 x 10(-9)-10(-5) mol/L) and ionomycin (4 x 10(-8)-10(-6) mol/L)-induced EDR in SHRSP aortae was significantly enhanced compared to that in WKY aortae. Mechanical denudation of the endothelium completely abolished, and pretreatment of aortae with NG-monomethyl L-arginine (1 mmol/L), an inhibitor of nitric oxide formation, greatly reduced the relaxation in both strains. Indomethacin (10(-5) mol/L), a cyclo-oxygenase inhibitor that blocks the production of endothelium-derived contracting factors, did not significantly alter the relaxation by acetylcholine at this age. There was no difference in endothelium-independent relaxation of denuded aortae by sodium nitroprusside (10(-9)-10(-6) mol/L) and 8-bromoguanosine 3', 5'-cyclic monophosphate (10(-6)-10(-3) mol/L). 3. In adult SHRSP with established hypertension, however, the acetylcholine (10(-8)-10(-5) mol/L)-induced relaxation markedly diminished at any of the concentrations tested compared to that observed in 8 weeks old SHRSP and WKY at 8-20 weeks of age. This finding differed from other observations where the relaxation in SHRSP was impaired only at higher concentrations of acetylcholine. Indomethacin pretreatment of aortae from 20 week old SHRSP restored acetylcholine-induced EDR to a level comparable with that in age-matched WKY.(ABSTRACT TRUNCATED AT 250 WORDS)

[A case of Fusobacterium necroforum sepsis]

A 26-year-old man was admitted to our hospital with a 10-day history of sore throat, high fever, and right knee joint pain. On physical examination, the pharynx was considerably inflamed, and the right knee joint was swollen and extremely tender. Chest radiography showed multiple, bilateral nodules and masses with pleural effusions. Fusobacterium necorforum grew from samples of blood, pleural effusion, and pus taken from the knee joint. The patient was treated with intravenous clindamycin, ventilatory support, and continuous chest and knee joint drainage. His condition progressively improved and he was discharged on the 66th hospital day. A disease caused by an oropharyngeal infection with secondary suppurative thrombophlebitis of the internal jugular vein, and complicated by multiple metastatic infections is called postanginal septicemia, or Lemierre syndrome. Before the discovery of antibiotics, this disease usually was fatal. The widespread use of antibiotics for treat oropharyngeal infections may have caused a number of reported cases. Lemierre syndrome is an uncommon complication of oropharyngeal infection, and it may be fatal if diagnosis is delayed. Careful attention must be directed to patients with oropharyngeal infection who have signs and symptoms that suggest metastatic infection.

Inhibition of EDRF release by native low-density lipoprotein from cultured porcine endothelial cells through intracellular mechanisms

Cyclic GMP accumulation in endothelial cells-smooth muscle cells (EC-SMC) coculture induced by both receptor-dependent (thrombin, bradykinin, BK) and receptor-independent (Ca(2+)-ionophore A23187) stimulation, was inhibited by preincubation with low-density lipoprotein (LDL) in time- and concentration-dependent manner. At least 5 min was necessary for the complete blockade with LDL (protein 1 mg/ml). LDL did not affect cyclic GMP-increase by sodium nitroprusside (SNP), a direct stimulator of SMC, but oxidized (ox)LDL (50-250 micrograms/ml) markedly reduced it. An increase of cyclic GMP accumulation in SMC by eluate from stimulated EC columns was completely blocked by 10-min pre-incubation of the column with LDL with or without superoxide dismutase (SOD). In contrast, preincubation of the SMC dish with LDL did not affect cyclic GMP accumulation by the eluate from the stimulated EC column, but preincubation with oxLDL (protein 50-100 micrograms/ml) greatly reduced it. Exposure time of released EDRF to LDL in both coculture and column experiments was < 40-45 s. These results suggest that a brief exposure of EC to pathophysiologic concentration of LDL exclusively affects EC functions, attenuating endothelium-derived relaxing factor (EDRF) release through intracellular mechanisms, and consumption of released EDRF by LDL does not appear to be involved in this LDL inhibitory effect. Possible inhibitory mechanisms of LDL are discussed.

Effects of intracellular pH on calcium currents and intracellular calcium ions in the smooth muscle of rabbit portal vein

In smooth muscle cells freshly dispersed from the rabbit portal vein, effects of intracellular pH (pHi) on Ca2+ channel currents were studied with the whole-cell clamp method using nystatin in the pipette. pHi was modified with ammonium chloride (NH4Cl) and propionate. Changes in intracellular Ca2+ concentration ([Ca2+]i) and pHi were also measured with the fluorescent indicator fura-2 and a pH-sensitive dye, respectively, together with the mechanical response in intact tissues. Intracellular alkalinization caused by an application of NH4Cl (20 mM) markedly potentiated and acidification caused by propionate (20 mM) inhibited inward Ca2+ channel currents, without much change in the kinetics. Tension development induced by 60 mM K- was inhibited by NH4Cl (20 mM) and potentiated by propionate (20 mM), whereas the peak [Ca2+]i level reached during K+ contracture was reduced in the presence of NH4Cl and increased in the presence of propionate. It was concluded that the modification of Ca2+ channel currents caused by pHi is not directly related to the effects of pHi on the mechanical response to excess K+. The direct effects of pHi on [Ca2+]i and on contractile machinery are considered to be mainly responsible for the mechanical effect of pHi.