Role of cellular superoxide dismutase against reactive oxygen metabolite injury in cultured bovine aortic endothelial cells

We examined the protective effect of cellular superoxide dismutase against extracellular hydrogen peroxide in cultured bovine aortic endothelial cells. 51Cr-labeled cells were exposed to hydrogen peroxide generated by glucose oxidase/glucose. Glucose oxidase caused a dose-dependent increase of 51Cr release. Pretreatment with diethyldithiocarbamate enhanced injury induced by glucose oxidase, corresponding with the degree of inhibition of endogenous superoxide dismutase activity. Inhibition of cellular superoxide dismutase by diethyldithiocarbamate was not associated either with alteration of other antioxidant defenses or with potentiation of nonoxidant injury. Enhanced glucose oxidase damage by diethyldithiocarbamate was prevented by chelating cellular iron. Inhibition of cellular xanthine oxidase neither prevented lysis by hydrogen peroxide nor diminished enhanced susceptibility by diethyldithiocarbamate. These results suggest that, in cultured endothelial cells: 1) cellular superoxide is involved in mediating hydrogen peroxide-induced damage; 2) superoxide, which would be generated upon exposure to excess hydrogen peroxide independently of cellular xanthine oxidase, promotes the Haber-Weiss reaction by initiating reduction of stored iron (Fe3+) to Fe2+; 3) cellular iron catalyzes the production of a more toxic species from these two oxygen metabolites; 4) cellular superoxide dismutase plays a critical role in preventing hydrogen peroxide damage by scavenging superoxide and consequently by inhibiting the generation of the toxic species.

Second messenger signaling in the regulation of cytosolic pH and DNA synthesis by parathyroid hormone (PTH) and PTH-related peptide in osteoblastic osteosarcoma cells: role of Na+/H+ exchange

The present study was performed to investigate the regulation of cytosolic pH (pHi) and DNA synthesis by parathyroid hormone(PTH) and PTH-related peptide (PTHrP) in osteoblasts, using osteoblastic osteosarcoma cells, UMR-106 which possessed PTH-responsive dual signal transduction systems (cAMP-dependent protein kinase (PKA) and calcium/protein kinase C [Ca/PKC]) and amiloride-inhibitable Na+/H+ exchange system. Both human (h)PTH-(1-34) and hPTHrP-(1-34) caused a progressive decrease in pHi and the inhibition of [3H]thymidine incorporation (TdR) to the same degree in a dose-dependent manner with a minimal effective dose of 10(-10) M. Dibutyryl cAMP (10(-4) M and Sp-cAMPS (10(-4) M), a direct stimulator of PKA also caused a progressive decrease in pHi, and calcium ionophores (A23187 and ionomycin, 10(-6) M) caused a transient decrease in pHi. Pretreatment with amiloride (0.3 mM) mostly blocked dbcAMP- and Sp-cAMPS-induced decrease in pHi but did not affect calcium ionophore-induced decrease in pHi. In the presence of amiloride, PTH and PTHrP caused a transient decrease in pHi, which was similar to the pattern of calcium ionophore-induced change in pHi. Amiloride did not affect the inhibition of TdR by PTH or PTHrP as well as that by cAMP analogues or calcium ionophores. The present study indicated that PTH and PTHrP caused cytosolic acidification through PKA-inhibited Na+/H+ exchange and increased cytosolic calcium-induced pathway and that the regulation of DNA synthesis by PTH and PTHrP was not via Na+/H+ exchange system.

[A case of acute renal failure in a patient with idiopathic hypouricemia]

This report is a 17-year-old man with an acute renal failure who complained of nausea, vomiting, bilateral loin pain and abdominal pain after scuffle. Renal biopsy specimen obtained from the left kidney revealed acute tubular necrosis. After recovering renal function he showed extreme hypouricemia (serum uric acid, 0.6 mg/dl) and elevated uric acid clearance (62-78 ml/min). The fractional excretion of uric acid (CUA/Ccr) could not be influenced by either oral pyrazinamide or probenecid. As no other renal tubular or metabolic abnormalities were detected, it is suggested that presecretory reabsorption defect or subtotal defect in uric acid transportation was responsible for the hypouricemia in this patient.

[Measurement of renal plasma flow and glomerular filtration rates in diabetic subjects]

To clarify the problem in the measurement of renal plasma flow and glomerular filtration rates in diabetes, the effect of glucose on the determination of para-aminohippuric acid (PAH) and inulin was examined. The concentration of urinary PAH in glucosuric diabetic subjects decreased after the storage of urine samples because of the glycation of PAH. Therefore, glucose must be removed by the acid treatment before the determination of the concentrations of urinary PAH. Since glucose can interfere with the assay of inulin, the sample must be treated with NaOH prior to the determination of the inulin concentration. GFR of the subjects with type 2 diabetes was next examined. GFR in the subjects with a duration of diabetes less than 10 years was significantly higher than that in the subjects with a duration of diabetes more than 10 years. Thus, the subjects with short-term type 2 diabetes may present with hyperfiltration similar to the subjects with short-term type 1 diabetes.

[Surgical treatment of active infective endocarditis and prosthetic valve endocarditis]

Fifteen patients with active native valve endocarditis (NVE) and 5 with prosthetic valve endocarditis (PVE) were subjected to this study. Among the patients with NVE, one of 10 with simple destruction of leaflets and 2 of 5 with annular infection died postoperatively of cerebral bleeding and persistent infection. Five patients with annular infection, whose microorganisms were Streptococcus faecalis, Staphylococcus epidermidis and gram-negative coccus, had a shorter duration from onset to operation (mean 38 days) compared with the others (mean 85 days). A patient with NVE requires an urgent operation, especially when these microorganisms are identified. Among those with PVE, 3 underwent operation at the active phase and one at the chronic phase. Two patients with mechanical valve endocarditis by Staphylococcus and Candida died, but the other 2 with bioprosthetic valve endocarditis by alpha-Streptococcus survived, because infection was localized in the leaflets. Another patient with mechanical valve endocarditis by alpha-Streptococcus survived with conservative management. While a patient with bioprosthetic valve endocarditis requires an early operation as well as NVE, a patient with mechanical valve endocarditis requires selected management considering the microorganism and general condition.

Noninvasive assessment of cardiomyopathy development with simultaneous measurement of topical 1H- and 31P-magnetic resonance spectroscopy

Background. It might be possible to estimate the metabolic derangement of cardiac muscle by topical nuclear magnetic resonance spectroscopy (MRS) in vivo without killing the animal. Methods and Results. By use of topical 1H- and 31P-MRS focused on the heart of Syrian hamsters with or without cardiomyopathy (CM; BIO 14.6 strain), the chemical constituents were measured in vivo nondestructively and repetitively at several stages of development of CM. A phantom experiment and two-dimensional plot of chain methylenes (CH2) of lipid/water ratio by 1H-MRS versus creatine phosphate (CP)/[beta-P]ATP ratio by 31P-MRS indicated that signal cross talk from the adjacent organs was negligible. Even before the onset of clinical or pathological manifestation of CM (7 weeks after birth), CH2/water ratio by 1H-MRS was lower in the CM group (7.3 +/- 0.7%) than in control (11.8 +/- 2.0%, p less than 0.05), and it decreased further at the hypertrophic stage (17 weeks, 4.1 +/- 0.7%, p less than 0.05) and the congestive stage (27 weeks, 4.3 +/- 0.9%, p less than 0.05). In contrast, the CP/[beta-P]ATP ratio by 31P-MRS started to decrease at the hypertrophic stage (1.90 +/- 0.18 versus 2.52 +/- 0.24, p less than 0.05) and decreased further at the congestive stage to 1.53 +/- 0.18 (p less than 0.01). These in vivo MRS data were confirmed by both biochemical assay and in vitro MRS analysis in heavy water after the animals were killed. Conclusions. A combination of topical 1H-MRS and 31P-MRS in vivo is promising for the noninvasive and sensitive assessment of cardiac muscle metabolism. Comparison of these MRS studies and biochemical analysis suggested not only the modification of water, lipid, CP, or ATP contents but also the reduction of flexibility or fluidity of lipids in cardiomyopathic heart.

[Surgical treatment of native valve endocarditis]

Twenty eight patients with native valve endocarditis (NVE) were subjected to this study. Thirteen patients underwent an operation at the chronic phase, and 15 patients at the active phase. One of the 13 patients at the chronic phase died of cardiac rupture due to myocardial infarction which had occurred preoperatively, and one of 10 patients at active phase without annular infection died of rupture of mycotic cerebral aneurysm early postoperatively. Among 5 patients at the active phase with annular infection, prosthetic valve endocarditis occurred in one patient 1.5 months after supraannular aortic valve replacement, and the second operation with a translocation technique was needed. This patient was lost from low output syndrome. Another patient in this group, who underwent a translocation technique because of mycotic annular abscess, died of intestinal infarction late postoperatively. The other 24 patients went a good postoperative course. Five patients with annular infection at the active phase had a shorter duration from the infectious onset to operation (20 days to 2 months, average 38 days), and the causative microorganisms were streptococcus faecalis, staphylococcus epidermidis and gram-negative coccus. One patient, who died of mycotic cerebral aneurysmal rupture, had candida albicans as a causative microorganism. For patients with NVE, an early aggressive operation is essential before infection extends to the annulus or to other vital organs, especially when these microorganisms are identified.

Severe hypoxia due to ventilation-perfusion mismatch caused by aortic arch aneurysm

We report a very rare case of hugh aortic arch aneurysm associated with aortic restenosis, which caused severe hypoxia due to ventilation-perfusion mismatch by compression of the left main bronchus and the right pulmonary artery. Aortic arch replacement was performed under circulatory arrest and deep hypothermia in addition to aortic valve replacement as a redo operation, and consequently such hypoxia was relieved.

[Coronary artery bypass grafting in patients with poor left ventricular function using retrograde continuous cold blood cardioplegia]

Patients with poor left ventricular function or those requiring urgent surgery may have more extensive ischemic myocardial injury if myocardial preservation is incomplete. We have performed coronary artery bypass grafting (CABG) aimed at complete revascularization in such cases using RC-CBCP, which is considered more effective on myocardial preservation during aortic cross-clamping in particular to protect ischemic area distal to severe coronary artery stenosis or obstruction. In the present study, in 25 patients with poor left ventricular function (left ventricular ejection fraction; LVEF less than or equal to 0.3) including 10 patients who required urgent surgery, the operative results were evaluated. All the distal and proximal anastomoses of grafts (average 2.5 grafts) were completed during one aortic cross-clamping using RC-CBCP, therefore graft flow was obtained immediately after release of the aortic clamping. Though this method required 142 minutes of a mean aortic cross-clamping time, myocardial protection was considered to be preferable judging from postoperative isoenzymatic evaluation and improved ventricular function. Fifteen patients with elective CABG were all alive and restored to NYHA class I to II. Among 10 patients requiring urgent CABG, 4 patients with acute myocardial infarction died but others were restored to NYHA class I to II. We conclude that it is important to aim at complete coronary revascularization in patients with poor left ventricular function and RC-CBCP achieves more effective myocardial protection during CABG in the patients.

Role of endogenous ANP in sodium excretion in rats with experimental pulmonary hypertension

To explore the roles of endogenous atrial natriuretic peptide (ANP) in the volume regulation, we examined effects of antiserum for ANP or a neutral endopeptidase inhibitor, thiorphan, in rats with monocrotaline (MCT)-induced pulmonary hypertension. ANP concentrations in the plasma and right ventricle and ANP mRNA in the right ventricle of MCT-treated rats were higher than in vehicle-treated rats. The administration of the ANP antiserum into the MCT-treated rats did not affect the right atrial pressure or blood pressure but significantly decreased urinary excretion of Na by 60%. No decrease occurred in the control rats. Thiorphan dose dependently increased the urinary excretion of Na by 140% without influencing the right atrial pressure or blood pressure. This natriuresis was associated with 50 and 450% increases in ANP concentrations in the plasma and urine, respectively. The degrees of increases in urinary Na excretion, ANP, and guanosine 3',5'-cyclic monophosphate were significantly greater in the MCT-treated rats than in the control rats. Thus an increased secretion of ANP in pulmonary hypertension actually contributes to Na excretion. The augmentation of endogenous ANP activity may further potentiate the compensatory role of this peptide in the regulation of body fluid volume.

Effects of the Fab fragment of digoxin antibody on the natriuresis and increase in blood pressure induced by intracerebroventricular infusion of hypertonic saline solution in rats

1. The effects of intravenous injection of Fab fragments of anti-digoxin IgG (Digibind) on the changes in blood pressure, urine volume and urinary sodium excretion after intracerebroventricular infusion of artificial cerebrospinal fluid with normal or high sodium concentration were examined in anaesthetized rats. 2. The biological efficacy of Digibind was confirmed by experiments in vitro and in vivo, which showed that pretreatment with Digibind completely abolished or significantly attenuated the aortic contractile response or pressor response to digoxin in guinea-pigs. 3. Infusion of high-sodium cerebrospinal fluid, but not normal-sodium cerebrospinal fluid, into the lateral brain ventricle of rats caused marked increases in blood pressure, urine volume and urinary sodium excretion. 4. Digibind did not significantly affect the increases in blood pressure, urine volume and urinary sodium excretion caused by intracerebroventricular infusion of high-sodium cerebrospinal fluid. 5. Digoxin-like immunoreactive factor may play a minor role, if any, in central nervous system-induced natriuresis in rats.

Acute acalculous cholecystitis complicating Mycoplasma pneumoniae infection

Mycoplasma pneumoniae infection has been associated with extrarespiratory manifestations. Gastrointestinal manifestations, gastroenteritis, hepatitis, and pancreatitis have also been reported.1,2 There have been no previous reports of acute cholecystitis complicating Mycoplasma pneumoniae infection. Acute acalculous cholecystitis is uncommon in childhood. We report on a child with acute cholecystitis during the course of Mycoplasma pneumoniae infection.

The effects of acid secretagogues on protective agents of gastric cells from adult rabbits in vitro

Endogenous prostaglandin and mucus have been recognized as important protective factors in the gastric mucosa. However, the regulatory mechanisms of these agents have not been well studied. The aim of the present study was to investigate the effects of acid secretagogues on cyclic adenosine monophosphate (cAMP) formation, prostaglandin E2 (PGE2) production, and mucus secretion by isolated parietal cells and culture mucous cells from adult rabbits. Rabbit parietal cells were enriched by nonlinear Percoll gradients after the isolation of rabbit gastric mucosal cells with collagenase and ethylenediaminetetraacetic acid (EDTA). Rabbit gastric mucous cells were cultured in 10% fetal bovine serum added to Ham's F12 medium. As gastric acid secretagogues, histamine, carbachol, gastrin, and 2-chloroadenosine were tested. To evaluate the effects of the second messengers of cellular signal transduction on protective agents, A23187, which is a calcium ionophore, and cAMP were used. PGE2 and cAMP were measured by radioimmunoassay. The release of [3H]glucosamine from prelabeled cells was used as an indicator of mucus secretion. Histamine, carbachol, gastrin, and 2-chloroadenosine did not modulate PGE2 production by parietal cells. Exogenously administered cAMP did not affect PGE2 production by parietal cells, whereas it was significantly increased by A23187. 2-Chloroadenosine but not histamine or carbachol significantly increased cAMP formation by mucous cells. Histamine, carbachol, and gastrin did not have significant effects on PGE2 production by mucous cells. 2-Chloroadenosine, which increased cAMP, also did not modulate PGE2 production. A23187 but not cAMP increased PGE2 production by mucous cells. None of the acid secretagogues used in the present study modulated mucus secretion. A23187 but not cAMP significantly increased mucus secretion by cultured mucus cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Interferon gamma attenuates hypertensive renal injury in salt-sensitive Dahl rats

Evidence has been provided that the immunological mechanism is involved in the genesis or maintenance of hypertension. In the present study, we investigated the effects of interferon gamma, a potent immunomodulator derived from lymphocytes, on hypertension and organ damage in Dahl salt-sensitive rats and in spontaneously hypertensive rats. Subcutaneous injection of interferon gamma (5 x 10(4) units/kg body wt once a week for 10 weeks) reduced blood pressure in Dahl salt-sensitive rats fed a 4% high salt diet (174 versus 194 mm Hg, p less than 0.025). This blood pressure reduction was associated with an improvement of renal functions, an increase in glomerular filtration rate (690 versus 569 ml/day/100 g body wt, p less than 0.05), and decreases in urinary protein excretion (48 versus 78 mg/day/100 g body wt, p less than 0.025) and urinary N-acetyl-beta-D-glucosaminidase excretion (143 versus 183 milliunits/day/100 g body wt, p less than 0.05). Morphological investigation showed a marked resolution of the vascular injuries seen in untreated Dahl salt-sensitive rats, e.g., intimal and medial hyperplasia, with infiltration of inflammatory cells, and significant amelioration of the glomerular sclerotic changes. In contrast, interferon gamma affected neither blood pressure nor renal functions in spontaneously hypertensive rats. These data indicate that interferon gamma ameliorates the development of hypertension and vascular and renal injuries in Dahl salt-sensitive rats. The resolution of vascular and renal injuries contributes, in part, to the antihypertensive action of interferon gamma.

Abnormal response of urinary eicosanoid system to norepinephrine infusion in patients with essential hypertension

To define the role of the renal eicosanoid system in sustaining renal homeostasis in hypertension, we investigated the alterations in urinary excretions of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), a stable metabolite of vasodepressor prostacyclin, and thromboxane B2 (TXB2), a stable metabolite of vasoconstrictor TXA2, when norepinephrine was continuously infused for 90 min in hypertensive (n = 13) and normotensive subjects (n = 14). There was no difference in plasma norepinephrine concentration after the infusion between the hypertensive and the normotensive subjects. Moreover, the percent changes in renal vascular resistance elicited by norepinephrine in the hypertensives were equal to those of the normotensive subjects. In the normotensive subjects, the norepinephrine infusion significantly increased urinary 6-keto-PGF1 alpha excretion and decreased urinary excretion of TX, both of which are beneficial for sustaining renal function. In fact, the greater the production of renal 6-keto-PGF1 alpha was, the less the reduction of renal blood flow and urinary sodium excretion was. In the hypertensive subjects, however, these normal responses of the renal eicosanoid system, seen in the normotensives, were abolished; urinary 6-keto-PGF1 alpha was unaltered and thromboxane generation was rather increased. Thus, the renal eicosanoid system dysfunctions in hypertensive subjects when the renal circulation is challenged by norepinephrine. These abnormal responses are likely to cause sodium retention and could contribute, in part, to the hypertensive mechanism in patients with essential hypertension.

On the mechanism of G protein beta gamma subunit activation of the muscarinic K+ channel in guinea pig atrial cell membrane. Comparison with the ATP-sensitive K+ channel

The mechanism of G protein beta gamma subunit (G beta gamma)-induced activation of the muscarinic K+ channel (KACh) in the guinea pig atrial cell membrane was examined using the inside-out patch clamp technique. G beta gamma and GTP-gamma S-bound alpha subunits (G alpha *'s) of pertussis toxin (PT)-sensitive G proteins were purified from bovine brain. Either in the presence or absence of Mg2+, G beta gamma activated the KACh channel in a concentration-dependent fashion. 10 nM G beta gamma almost fully activated the channel in 132 of 134 patches (98.5%). The G beta gamma-induced maximal channel activity was equivalent to or sometimes larger than the GTP-gamma S-induced one. Half-maximal activation occurred at approximately 6 nM G beta gamma. Detergent (CHAPS) and boiled G beta gamma preparation could not activate the KACh channel. G beta gamma suspended by Lubrol PX instead of CHAPS also activated the channel. Even when G beta gamma was pretreated in Mg(2+)-free EDTA internal solution containing GDP analogues (24-48 h) to inactivate possibly contaminating G i alpha *'s, the G beta gamma activated the channel. Furthermore, G beta gamma preincubated with excessive GDP-bound G o alpha did not activate the channel. These results indicate that G beta gamma itself, but neither the detergent CHAPS nor contaminating G i alpha *, activates the KACh channel. Three different kinds of G i alpha * at 10 pM-10 nM could weakly activate the KACh channel. However, they were effective only in 40 of 124 patches (32.2%) and their maximal channel activation was approximately 20% of that induced by GTP-gamma S or G beta gamma. Thus, G i alpha * activation of the KACh channel may not be significant. On the other hand, G i alpha *'s effectively activated the ATP-sensitive K+ channel (KATP) in the ventricular cell membrane when the KATP channel was maintained phosphorylated by the internal solution containing 100 microM Mg.ATP. G beta gamma inhibited adenosine or mACh receptor-mediated, intracellular GTP-induced activation of the KATP channel. G i alpha *'s also activated the phosphorylated KATP channel in the atrial cell membrane, but did not affect the background KACh channel. G beta gamma subsequently applied to the same patch caused prominent KACh channel activation. The above results may indicate two distinct regulatory systems of cardiac K+ channels by PT-sensitive G proteins: G i alpha activation of the KATP channel and G beta gamma activation of the KACh channel.

Biologic activities of parathyroid hormone (1-34) and parathyroid hormone-related peptide (1-34) in isolated perfused rat femur

Parathyroid hormone-related peptide (PTHrP) has substantial homology with both human and rat parathyroid hormone (66% and 73%, respectively) in the first 15 amino acids. PTHrP (1-34) stimulates cyclic adenosine monophosphate (cAMP) release in bone and kidney, and these effects are felt to occur through interaction with the parathyroid hormone (PTH) receptor. Differences in the biologic potency between rat PTH(1-34) and human PTH(1-34)--and between PTHrP and PTH--have been described in a variety of experimental systems. In this study, we compared the bioactivity of these three amino-terminal synthetic fragments on the stimulation of cAMP formation in an isolated perfused rat femur preparation. Dose-response experiments demonstrated that PTHrP(1-34) was more potent in stimulating cAMP release than human PTH(1-34), whereas PTHrP(1-34) and rat PTH(1-34) were equipotent. Despite the fact that the extraction of immunoreactive rat PTH(1-34) and human PTH(1-34) was the same, rat PTH(1-34) was more potent in stimulating adenylate cyclase activity than human PTH(1-34). These data show that the isolated perfused rat femur preparation is an effective method for evaluation of the effects of PTH and PTHrP. Despite significant structural differences in the binding domain between rat PTH(1-34) and PTHrP(1-34), the effects of rat PTH(1-34) and PTHrP(1-34) are similar. Because the structure of rat PTHrP(1-34) and human PTHrP(1-34) are identical, and because it is desirable to utilize homologous systems to study the potency and effects of test peptides, it would appear that rat PTH(1-34) is the most appropriate peptide for comparison with PTHrP in rat-based experimental systems.

Abnormal metabolism of carnitine and valproate in a case of acute encephalopathy during chronic valproate therapy

We analyzed the urinary metabolic profiles of valproate (VPA) and carnitine metabolism in an epileptic patient who died of acute encephalopathy during VPA therapy. On admission, the serum free carnitine level was greatly decreased and gas chromatographic mass spectrometric analysis of organic acids in urine showed a complete lack of beta-oxidation metabolites of VPA, while omega-oxidation was markedly increased. After administration of L-carnitine, the levels of acylcarnitine in both serum and urine, and of serum free carnitine increased, and the metabolites of beta-oxidation appeared in urine, while there was no improvement in the liver and renal functions. This is not a typical case of VPA-induced hepatotoxicity and the main cause of the disease is not clear. But the results show that the mitochondrial beta-oxidation of VPA was greatly disturbed in this patient, which may be related to the carnitine deficiency induced by the chronic VPA-therapy.

Cardiac adaptation and its limitation in an experimental model of congestive heart failure

To elucidate mechanisms of adaptation and maladaptation in heart failure, abnormalities of left ventricular function and their relationships to myocardial contractile protein were studied in the Syrian hamster Bio 14.6. Left ventricular and heart weights were both increased in 20-week-old cardiomyopathic hamsters, indicating cardiac hypertrophy as a compensatory mechanism to the disease process of cardiomyopathy. However further increase in the left ventricular weight was not observed in older (40-week-old) cardiomyopathic hamsters. On the other hand left ventricular volume and volume/mass ratio were increased progressively. Correspondingly, V3 type myosin was increased and myosin sliding velocity was decreased. Left ventricular function of cardiomyopathic hamsters evaluated using an isovolumically beating perfused heart preparation was depressed, and this functional impairment was also progressive. Chronic administration of metoprolol, a beta-blocking agent, induced further increase in left ventricular volume and mass without changing left ventricular function and myosin isozyme pattern. Thus in cardiomyopathic hamsters, left ventricular function progressively deteriorates in spite of a variety of adaptive mechanisms, and remodeling occurs.

Active movement of cardiac myosin on Characeae actin cables

The active sliding of cardiac myosin on actin cables was studied using an in vitro movement assay. Cardiac myosin prepared from either adult rabbit or rat hearts was mixed with small latex beads to coat them. Actin cables were obtained from the internodal cells of green algae, Characeae. When the myosin-coated beads suspended in physiological buffer were introduced into the internodal cells, the myosin started to interact with the actin causing the beads to move. The sliding movement of the beads was observed under microscopy and the sliding velocity measured. The observed movement was smooth and the velocity was constant over a long distance. The movement was physiological in nature: a) it was ATP-dependent, but above a certain level of ATP, the velocity was constant; b) the velocity was maximum at pH 7.0, and decreased in both acidic and alkaline conditions. The average sliding velocity of cardiac myosin obtained from rabbit ventricles (0.31 +/- 0.11 micron/s) was slower than that from rat ventricles (1.04 +/- 0.26 micron/s) reflecting the lower ATPase activity of rabbit cardiac myosin. This assay system is considered to be a useful tool linking biochemistry and physiology at the molecular level.

Effects of anions on the G protein-mediated activation of the muscarinic K+ channel in the cardiac atrial cell membrane. Intracellular chloride inhibition of the GTPase activity of GK

The effects of various intracellular anions on the G protein (GK)-mediated activation of the muscarinic K+ (KACh) channel were examined in single atrial myocytes isolated from guinea pig hearts. The patch clamp technique was used in the inside-out patch configuration. With acetylcholine (ACh, 0.5 microM) in the pipette, 1 microM GTP caused different magnitudes of KACh channel activation in internal solutions containing different anions. The order of potency of anions to induce the KACh channel activity at 0.5 microM ACh and 1 microM GTP was Cl- greater than or equal to Br- greater than 1-. In the SO4(2-) or aspartic acid internal solution, no channel openings were induced by 1 microM GTP with 0.5 microM ACh. In both the Cl- and SO4(2-) internal solutions (with 0.5 microM ACh) the relationship between the concentration of GTP and the channel activity was fit by the Hill equation with a Hill coefficient of approximately 3-4. However, the concentration of GTP at the half-maximal activation (Kd) was 0.2 microM in the Cl- and 10 microM in the SO4(2-) solution. On the other hand, the quasi-steady-state relationship between the concentration of guanosine-5'-o-(3-thiotriphosphate) and the channel activity did not differ significantly between the Cl- and SO4(2-) solutions; i.e., the Hill coefficient was approximately 3-4 and the Kd was approximately 0.06-0.08 microM in both solutions. The decay of channel activity after washout of GTP in the Cl- solution was much slower than that in the SO4(2-) solution. These results suggest that intracellular Cl- does not affect the turn-on reaction but slows the turn-off reaction of GK, resulting in higher sensitivity of the KACh channel for GTP. In the Cl- solution, even in the absence of agonists, GTP (greater than 1 microM) or ATP (greater than 1 mM) alone caused activation of the KACh channel, while neither occurred in the SO4(2-) solution. These observations suggest that the activation of the KACh channel by the basal turn-on reaction of GK or by phosphate transfer to GK by nucleoside diphosphate-kinase may depend at least partly on the intracellular concentration of Cl-.