Spermidine synthase of Escherichia coli: localization of the speE gene.

We have obtained Escherichia coli mutants lacking spermidine synthase (putrescine aminopropyltransferase) and have found that the mutated gene (speE) is located immediately upstream from the gene coding for S-adenosylmethionine decarboxylase (speD); these genes are located at 2.7 minutes on the E. coli chromosome. Both genes are present in a 1795-base-pair fragment of E. coli DNA that was cloned into pBR322. Deletion of 105 bases upstream of speE caused a coordinate loss of both activities, indicating that speE and speD constitute a single operon. speE and speD have also been cloned separately in a high-expression vector; strains carrying these plasmids overproduce the respective enzymes.     

Effect of gradual rise in plasma calcium concentration on the impairment of atrioventricular nodal conduction due to verapamil

The possible reversal by calcium of the inhibitory action of verapamil on the atrioventricular (AV) node was investigated in anesthetized, atropinized dogs, with cardiac pacing. The His bundle potentials were recorded by endocavitory electrode and the AV node effective refractory period measured by the extrastimulus method. Calcium infusion was effective against the impairment of AV nodal conduction induced by verapamil, provided it remained moderate: the gradual rise in the plasma calcium concentration counteracted the effects of an infusion of verapamil on conduction time and effective refractory period in the AV node, as long as it did not exceed 5 mmol/L. However, beyond this level, calcium appeared less and less capable of reversing the effects of verapamil. Thus, the protective action of calcium had a bell-shaped dose-response curve, with the optimum at 5 mmol/L. This biphasic influence is consistent with the opposite opinions previously given concerning the antagonism between calcium and calcium blockers, depending on whether hypercalcemia brought into play was mild or major. In any case, the prominent role played by calcium in the slow inward current in the AV node accounts for the antagonism, observed in vivo, between calcium and verapamil. The pacemaker activity of the sinoatrial (SA) node was less influenced by both calcium blocker and calcium.     

Functional recognition of the neuronal tyrosine hydroxylase cAMP regulatory element in different cell types.

Transient transfection of pLB2CAT constructs bearing short synthetic oligonucleotides derived either from the tyrosine hydroxylase (TH) promoter or other sources was used to examine functional cAMP regulatory element (CRE) activity in a variety of cell lines. The region containing only the putative TH CRE was found to be as or more effective in conferring cAMP responsiveness onto pLB2CAT (which employs the TK promoter) than the immediate 272 bp region of the TH promoter. Increases in CAT activity of 10- to 20-fold were observed in JEG-3 cells with a single insert of the TH CRE region (-31 to -54) in pLB2CAT, and the presence of a second insert generated only a modest further increase. This construct also responded to cAMP in 4 other cell lines tested but the degree of increase was less dramatic. Inserts containing the consensus 8 bp CRE motif embedded in other natural or artificial contexts served generally as weak functional CREs in all cell lines tested. In vitro analysis revealed that a specific protein-DNA complex apparently containing a single protein with a MW of 45-50 kDa was formed equally well with JEG-3 cell nuclear extract and CRE-bearing-TH and other fragments which produced dramatically different cAMP effects in vivo. These results suggest specificity in the effects of cAMP on different CREs which are dictated by contextual differences.     

Calcium-activated proteolysis of intracellular domains in the cell adhesion molecules NCAM and N-cadherin.

One of the consequences of increased intracellular calcium in response to a variety of physiological stimuli is the calcium activation of cytosolic proteases. Unlike lysosomal proteases with broad specificity, these calcium-activated neutral proteases show limited proteolysis of a restricted set of substrate proteins suggesting they may play a regulatory role in cellular physiology. In this study we show that the neural cell adhesion molecules NCAM-180 and N-cadherin are substrates for such endogenous calcium-activated neutral proteases. In contrast, a third neural cell adhesion molecule G4/L1 was not susceptible to calcium-activated proteolysis. The threshold for activation of NCAM and N-cadherin proteolysis is in the micromolar range of calcium suggesting that NCAM and N-cadherin are substrates for a mu-type calpain (calpain I). The site recognized by this protease is within intracellular domains of NCAM-180 and N-cadherin which are important for their interaction with cytoskeletal components. These results suggest that calcium-activated proteolysis at these sites in vivo could disrupt the linkage between extracellular ligand binding to these adhesion molecules and the normal intracellular effectors of such extracellular binding events.     

Intracellular Ca2+ suppressed a transient potassium current in hippocampal neurons

The effects of intracellular Ca2+ (Ca2+i) on K+ currents in hippocampal cells were examined using acutely isolated cells obtained from adult guinea pigs. Whole-cell voltage-clamp recordings were carried out in a configuration that allowed a continuous perfusion of the intracellular medium. Recording media were made to block inward currents and allowed selective activation of K(+)-dependent outward currents. Voltage-dependent outward currents consisted of an initial rapidly decaying component followed by a sustained component. The time constant of decay of the transient current was about 25 msec, and previous studies (Numann et al., 1987) showed that the kinetic and pharmacological properties of this current closely resembled the A current recorded in invertebrate neurons (Connor and Stevens, 1971; Thompson, 1982). Intracellular perfusion of hippocampal cells with a solution containing elevated Ca2+ (about 4.5 x 10(-4) M) elicited outward currents at the holding potential (-45 to -55 mV) and produced changes in voltage-dependent K+ currents. The transient outward current (IA) activated by depolarization was suppressed with increases in Ca2+i. Delayed, sustained K+ currents were greatly potentiated. Data also showed that, among the 3 effects elicited by Ca2+i, suppression of IA was most sensitive to Ca2+i elevation. Previous results (Numann et al., 1987) showed that IA had a lower threshold (about -45 mV) than sustained currents (about -40 mV). By using low levels of depolarization (-40 mV), IA can be selectively activated, and the suppressive effect of Ca2+i on IA was confirmed on the kinetically isolated IA.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lithium-induced changes in the body mass index

A total of 117 manic-depressives who had been on lithium for a mean duration of 4.7 years were examined before lithium therapy and subsequently at intervals. Information relating to pre-lithium height and weight and current weight were determined and used to calculate the body mass index (BMI) for each individual. Other relevant variables such as age, sex, cumulative lithium dose, duration of therapy, thyroid profile and serum lithium levels were recorded. The results indicated that, although there was a nonsignificant increase in BMI for the whole population, lithium and sex were not significant predictors of any increase in BMI. In nearly 27% of patients BMI actually slightly decreased during lithium therapy. The overall conclusions from this study are that, in the population studied, lithium may not have exerted any pharmacological effects to increase BMI.     

Treatment of ulcerative colitis by traditional Chinese medicine and dynamic study of immune functions

The effect of the traditional Chinese medicinal herbs enema and enteric-coated capsules in the treatment of ulcerative colitis (UC) were compared in 260 cases. The immune complexes and the dynamic change of autoantibodies were monitored in 28 out of the 260 cases before and after treatment. The following results were observed. (1) There was no significant difference in the total effective rate between the enema group and the oral capsule group (93.3% and 87.5% respectively), but the recovery rates of purulent hemafecia, mucusfecia and erosion accompanying colitis, etc. in the former group were higher than those in the latter (P less than 0.01). (2) The circulating immune complexes were found 43 times above the normal range in 17 cases with positive rate 60.7%, and tended to decrease as the condition became better after treatment. Antinuclear antibodies were determined by the indirect fluorescent immune method and the indirect enzyme labelling method and the positive rates were 53.6% and 64.7% respectively, both being much higher than those in the controls (P less than 0.01).