Mechanism and properties of inhibition of purified rat brain adenylate cyclase by G protein beta gamma-subunits

The mode of the inhibition of purified rat brain adenylate cyclase by the beta gamma-subunits of G protein (beta gamma) was studied. These subunits inhibited the catalytic activity of the cyclase with the maximal inhibition of 85% and the half-maximal inhibition at about 0.7 nM beta gamma. The complex of beta gamma and adenylate cyclase isolated by density gradient centrifugation contained 1.8-2.0 mol beta gamma per mol of the cyclase when beta gamma was assayed by immunoblotting and by its inhibitory activity on adenylate cyclase. However, the beta gamma concentration-inhibition curves suggest that one of the two beta gamma molecules bound may be essential for the inhibition. The role for the second beta gamma molecule is unknown. As a tentative estimate, 70% of the adenylate cyclase activity remained inhibited by beta gamma when the complex was isolated. The inhibition was not dependent on G alpha s or calmodulin. Although purified adenylate cyclase contained a protein (0.06-0.08 mol/mol of adenylate cyclase) that reacted with anti-G alpha s antibody, this protein was not liberated from the cyclase when it formed a complex with beta gamma. In addition, guanine nucleotide analogs little affected the cyclase activity or the inhibition by beta gamma. The inhibition by beta gamma was reversed by the dilution of the complex, and the following re-addition of beta gamma suppressed the enzyme activity to about 15% of the initial activity again. These findings provide strong evidence that beta gamma inhibits adenylate cyclase directly and reversibly through the formation of the complex.

G protein beta gamma-subunits inhibit purified adenylate cyclase independent of the activation by Ca2+ and calmodulin

Adenylate cyclase purified by affinity chromatography was activated about 2.5-fold in a Ca(2+)- and calmodulin-dependent fashion. G protein beta gamma-subunits, an inhibitor in the receptor-mediated inhibition of adenylate cyclase, inhibited the purified cyclase by more than 80%. The extent of beta gamma-induced inhibition was not affected by the activation with Ca2+ and calmodulin. Moreover, the prior addition of the beta gamma-subunits to the cyclase did not prevent the subsequent activation of the enzyme by Ca2+ and calmodulin. We conclude that the beta gamma-subunits inhibit adenylate cyclase activity in a calmodulin-independent mode.

Continuous assessment of hemodynamic control by complex demodulation of cardiovascular variability

Usefulness of complex demodulation (CDM) in assessing the frequency components of cardiovascular variability was assessed and, subsequently, this technique was utilized to determine the time-dependent responses of the low-frequency (LF) and high-frequency (HF) amplitudes of heart rate and blood pressure variabilities during postural tilt. CDM provides the time-dependent changes in amplitude of a particular frequency component on a continuous basis. Analysis of simulated data showed that CDM has sufficient frequency resolution to separately measure LF and HF amplitudes with a time resolution < 15 s and that CDM is robust to alterations in the frequency of the components. Analysis of actual data during postural tilt test in 23 young healthy subjects demonstrated that the HF amplitude of heart rate, an index of cardiac parasympathetic tone, rapidly decayed with head-up tilt (P < 0.01) and increased quickly showing an overshoot with tilt back to the supine position (P < 0.01). The LF amplitude of blood pressure, an index of vasomotor sympathetic activity, showed marked rhythmic fluctuation at an interval of 48-100 s during head-up tilt (P < 0.01), synchronizing with similar fluctuation in the LF amplitude of heart rate (P < 0.01). These results suggest that CDM can be used to provide a continuous assessment of cardiovascular variability components and that the dynamic responses of autonomic circulatory control to upright posture result in a phasic modulation of LF amplitude.

[Structure of adenylate cyclase and the coupling with the receptor-G protein system]

Adenylate cyclase is a key enzyme that couples with both the stimulatory and inhibitory G proteins (Gs and Gi). The cyclase has been purified and shown to be a glycoprotein of molecular weight 115,000-180,000. Cloning of cDNAs for adenylate cyclase showed that the cyclase is a member of a large family consisting of a variety of subtypes of the enzyme. These subtypes show different responses to calmodulin and G protein beta gamma subunits, and their distributions in tissues and organs are also different. This suggests that each subtype is involved in a particular physiological function. The general structure of adenylate cyclase is composed of two cytoplasmic domains and two membrane-spanning domains, each of which contains 6 transmembrane spans (12 spans in a molecule). The amino acid sequence of each cytoplasmic domain, which is thought to contain a nucleotide (ATP) binding site, is well-conserved among the various subtypes. This review also focuses on the regulation of adenylate cyclase activity by G protein subunits, particularly on several models for adenylate cyclase inhibition by Gi. As one of these mechanisms, direct inhibition of adenylate cyclase by the beta gamma subunits recently demonstrated by us will be discussed.

Single administration of captopril and combined use with beta-blocker and/or thiazide diuretic in the treatment of essential hypertension

Thirty-four patients with essential hypertension at WHO stage I or II were divided into three groups. Group I consisted of 22 cases who displayed normal renin activity (NR) or low renin activity (LR) and who received a single administration of captopril. Group II consisted of 6 cases given beta-blockers after administration of captopril. Group III consisted of 6 cases in whom beta-blocker was replaced with thiazide diuretics after administration of captopril alone. Blood pressure decreased significantly by captopril treatment alone in group I of the NR and LR subgroups (except for the diastolic blood pressure [DBP] of the NR subgroup) and fell below the target blood pressure (SBP of 165 mmHg and DBP of 95 mmHg) in 86% of the NR subgroup and 73% of the LR subgroup. Combined treatment with captopril and beta-blocker in Group II did not decrease blood pressure any lower than with captopril alone treatment and achieved the target blood pressure in only 50% of the patients. In group III, combined treatment with captopril and thiazide achieved the target blood pressure in 100% of the patients. Plasma renin activity (PRA) was increased by captopril but reduced by captopril in combination with beta-blocker. However, when beta-blocker was replaced with thiazide, PRA increased. The serum sodium concentration was significantly reduced in the LR subgroup after a single administration of captopril, but there was no other variation.

ADP-ribosylation of myelin basic protein by cholera toxin

Cholera toxin ADP-ribosylates four types of myelin basic proteins (MBPs) of Mr 14,000, 17,500, 19,000 and 22,000 in rat brain myelin. On an analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, MBP underwent mono- and multi-(ADP-ribosyl)ation by cholera toxin and thus modified MBP migrated on the gel as several discrete protein bands, the molecular masses of which were apparently larger by 500-2000 daltons than that of the corresponding untreated MBP. On average, 1.1 mol of ADP-ribosyl residue was incorporated into 1 mol of MBP. Four types of purified MBPs were also ADP-ribosylated by cholera toxin dependent on GTP and the protein factor for the ADP-ribosylation. The results show evidence that MBP is one of major and specific substrates of cholera toxin in brain membranes.

Two isoforms of regulatory light chain of abalone smooth muscle myosin

Abalone myosin contains two kinds of light chain, regulatory light chain (LC2) and essential light chain (LC1) according to SDS-PAGE. Three distinct light chain bands were observed on polyacrylamide gel electrophoresis of purified abalone myosin in the presence of urea (urea-PAGE). The slower two components showed had mobility on SDS-PAGE and they also showed regulatory activity as the regulatory light chain. They were termed LC2-a and LC2-b in order of increasing mobility on urea-PAGE and isolated by DE-32 ion exchange column chromatography in the presence 8 M urea. The ratio of LC2-a and LC2-b in the central portion of adductor muscle of abalone (LC2-a: LC2-b = 7:3) was different from that (1:1) in the peripheral portion. These results suggest that the two light chains are isoforms of the regulatory light chain. The amino acid compositions of LC2-a and LC2-b were very similar to each other except for the Cys content. The UV absorption spectra were also quite similar, as were the UV difference absorption spectra induced by Ca2+. Phosphorylation was not detectable with the myosin light chain kinase of chicken gizzard. The Ca2+ concentration dependencies of Mg-ATPase activity of LC2-a or LC2-b hybridized abalone myosin (a-myosin, b-myosin) were similar to each other in the absence of rabbit F-actin, but differed in the presence of actin. The b-myosin had a higher maximum value of actomyosin ATPase activity and a lower apparent binding constant of actin and myosin than a-myosin.(ABSTRACT TRUNCATED AT 250 WORDS)

Is extensive lymphadenectomy necessary for surgical treatment of intramucosal carcinoma of the stomach?

This study was undertaken to elucidate those histological and gross features associated with gastric carcinoma that can be adequately treated by gastrectomy with less aggressive lymphadenectomy. The frequency of metastasis to the lymph nodes was analyzed in 514 cases of resected, solitary, gastric carcinomas. The frequency of metastasis to the lymph nodes increased in proportion to the increase in the extent of penetration by the cancer into the gastric wall. Lymph nodes were not involved in cases of intramucosal carcinoma of the intestinal type, by Laurén's histological classification. By contrast, metastasis to the lymph nodes was observed in cases of intramucosal carcinoma of the diffuse type, by Laurén's classification. We conclude that extensive lymphadenectomy is not mandatory for patients with intramucosal carcinoma of the stomach of the protruded type, since the lymph nodes do not become involved in this type of gastric carcinoma.

Preparation of subfragment-1 from abalone smooth muscle myosin

Myosin subfragment-1 (S1), which has one heavy chain (HC) (93 kDa) and two light chains (LC1 and LC2), was prepared by papain digestion of myosin from abalone-smooth muscle in the presence of Ca2+. The Ca-sensitivity of abalone S1 itself was not lost completely (about 30%). The tryptic digestion of S1 showed that in the presence of EDTA, S1 HC was split into 68, 55, and 23 kDa fragments, as in the presence of Ca2+, but 23 kDa was further degraded into 19 kDa. In contrast to the result in the presence of Ca2+, LCs disappeared in the early stage of reaction and Ca-ATPase activity decreased rapidly to about 70% of that of intact S1. This rapid decrease of Ca-ATPase activity seemed to be accompanied with the digestion of LCs. Therefore, LCs contribute to the protection of 23 kDa fragment from further digestion, to the maintenance of Ca-ATPase activity by stabilizing the structure of S1 to some extent in the presence of Ca2+. Since F-actin suppressed the cleavage of S1 HC to 68 and 23 kDa during tryptic digestion, it might be that 23 and 68 kDa corresponded to 20 kDa (C-terminal fragment) and to 50 + 25 kDa (N-terminal fragment) of skeletal myosin S1, respectively.

The chromosomal normality of in vitro-fertilized rabbit oocytes

The chromosomal normality of rabbit oocytes fertilized in vitro was examined. Ovum donors were superovulated with pregnant mare's serum gonadotropin and human chorionic gonadotropin (hCG). Follicular oocytes were collected laparoscopically 9-10 h after hCG treatment and incubated in vitro with spermatozoa capacitated in vivo. Of 267 aspirated oocytes, 191 (71.4%) were fertilized in vitro and developed to the 2- to 8-cell stage 24-48 h after insemination. In the chromosomal studies, 121 (63.4%) were examined. Of these, 94 (77.7%) had a normal diploid complement of chromosomes (2n = 44) and 6 (5%) showed aneuploidy. Of the remaining 21, 20 were triploid and one was tetraploid. The incidence of triploid oocytes after in vitro fertilization was higher than the rate in vivo (16.5% vs. 9.0%, respectively). These triploid oocytes were suspected to be the result of polyspermic fertilization in vitro. In addition, at the Metaphase II stage, 62 (89.9%) of 69 induced, preovulatory oocytes had a normal number of chromosomes.

[Basic and clinical studies on ceftriaxone in perinatal infections]

Basic and clinical investigations were conducted on ceftriaxone (CTRX), a cephem antibiotic with a wide antibacterial spectrum and with especially high activity against Gram-negative bacteria. The results obtained are summarized as follows: 1. CTRX, following intravenous drip infusion of 1 g, had a serum half-life of 5.8 hours, which is longer than that of any other existing cephem antibiotics. 2. The level of CTRX in the umbilical cord serum 6 hours after intravenous drip infusion of 1 g was at a satisfactory level, 15 micrograms/ml. 3. The CTRX was remarkably effective or effective in 9 cases, and the activity was high even in cases where penicillin or other third-generation cephems were ineffective. These results seem to indicate that CTRX may be effective in perinatal and intrauterine fetal infections.