Potassium depletion selectively inhibits sustained diacylglycerol formation from phosphatidylinositol in angiotensin II-stimulated, cultured vascular smooth muscle cells

Potassium depletion decreases blood pressure in vivo and blunts the pressor response to angiotensin II (ang II) without down-regulating the receptor. In cultured rat aortic smooth muscle cells, the ang II-induced signaling sequence is biphasic with rapid hydrolysis of the polyphosphoinositides producing an early (15 s) diacylglycerol (DG) peak and a transient rise in inositol trisphosphate (IP3) and more delayed phosphatidylinositol (PI) hydrolysis resulting in sustained DG formation (peak at 5 min). Exposure of intact vascular smooth muscle cells to low potassium growth medium for 24 h or acutely potassium-depleting cells with nigericin causes selective, marked inhibition of late DG formation (5-min peak inhibited by 60 +/- 8% and 84 +/- 7%, respectively). The early cell response, namely polyphosphoinositide hydrolysis, inositol bis- and trisphosphate production and the 15-s DG peak, is not affected. Analysis of 125I-ang II-binding data reveals no significant differences in either receptor number or binding affinity (Kd) in potassium-depleted cells. Together with its marked inhibitory effect on sustained ang II-induced DG formation, acute potassium depletion effectively blocks internalization of 125I-ang II: there is no significant internalization of the ligand after 5 min at 37 degrees C versus 64 +/- 7% internalization in control cells. Thus, potassium depletion does not alter ang II binding or initial membrane signaling in rat aortic smooth muscle but blocks ligand internalization and selectively and markedly inhibits the development of direct PI hydrolysis and sustained diacylglycerol formation. These findings suggest a role for ligand-receptor processing in generating the sustained cell response and potentially explain the lower blood pressure and decreased pressor response to ang II seen in hypokalemic states in vivo. Furthermore, the ability of K+ depletion to alter secondary signal generation may provide insight into the mechanisms underlying the K+ dependence of a variety of cell functions.     

Comparative study of the effect of L-lysine-L-oxidase from Trichoderma harzianum Rifai and Trichoderma viride on nucleic acid synthesis in human tumor cells in vitro

L-lysine-alpha-oxidase, a new fungal enzyme catalyzing oxidative deamination of L-lysine, exerts an inhibitory effect on DNA, RNA and protein synthesis in human cells of carcinoma ovarius (CaOv) in vitro.     

Modification of testicular and thyroid function by chronic exposure to short photoperiod: a comparison in four rodent species

Exposure of male Syrian hamsters (Mesocricetus auratus) for 10 weeks to short photoperiod (SP) providing 10 hr light: 14 hr darkness (10:14 LD) produced a significant reduction in the weights of the reproductive organs, plasma thyroxine (T4) levels and free T4 index (FT4I) compared to the values of animals exposed to long photoperiod (LP, 14:10 LD). C57bl male house mice (Mus musculus) kept in SP (10:14 LD) had reproductive organ weights equivalent to those of mice kept in long days (14:10 LD) and lower T3 uptake (T3U) values. Male gerbils (Meriones unguiculatus) exposed to 13 weeks of SP (10:14 LD) had lower body weights, testes and seminal vesicle weights and higher T3U values compared to LP (14:10 LD) controls. However, no effect was seen on plasma T4 and triiodothyronine (T3) values nor the FT4I and free T3 index (FT3I). White-footed male mice (Peromyscus leucopus) exposed to SP (8:16 LD) had significantly lower testes and seminal vesicle weights while plasma T4 and T3 levels were unaffected. Snell strain house mice (Mus musculus) exposed to SP (8:16 LD) had normal reproductive organ weights compared to the values of LP-exposed (16:8 LD) control animals. However, there was a significant depression in T3 and in the FT3I in the SP animals.     

Effect of benzodiazepines on 5'-nucleotidase activity in rat brain

Experiments on 330 rats were made to study the influence of benzodiazepines (diazepam, dormicum and phenazepam) on 5'-nucleotidase activity in brain homogenates. It was discovered that diazepam and dormicum in doses of 3 and 4 mg, phenazepam in doses of 3.75 and 5 mg per 200 g bw provoked a 16-20% reduction in 5'-nucleotidase activity. The maximal effect of diazepam (3 and 4 mg doses) was attained 1 h after intraperitoneal injection, that of dormicum (3 mg) 30 min and of phenazepam (5 mg) 1 h after intraperitoneal injection. It is assumed that benzodiazepines are involved in AMP metabolism.     

Alterations in cerebrospinal fluid uridine,hypoxanthine, and xanthine in head-injured patients

1. Examination of the cerebrospinal fluid (CSF) of head-injured patients reveals that the concentration of intraventricular xanthine is elevated and that of uridine is decreased relative to those of adult lumbar CSF. 2. No correlations were observed between CSF lactate and CSF hypoxanthine, xanthine, or uridine, suggesting that changes in purine metabolites and the pyrimidine nucleoside do not index similar cellular events as does lactic acid production. 3. Ventricular CSF from hydrocephalic infants had uridine and hypoxanthine concentrations not significantly different from those of normal adult lumbar CSF, but xanthine was significantly elevated. 4. Since uridine has anticonvulsant properties and is a crucial substrate for cerebral metabolism, it may be useful to evaluate this pyrimidine for use in the management of patients with head injury.     

Spontaneous fibrinolysis in whole human plasma. Identification of tissue activator-related protein as the major plasminogen activator causing spontaneous activity in vitro

Spontaneous fibrinolysis of plasma clots was studied by following the lysis of the clots formed in 125I-fibrinogen-supplemented citrated plasma. Lysis of the clots invariably follows sigmoidal kinetics with S50 (the time required for 50% clot lysis) ranging from 3.5 to 4.7 days in 8 samples of pooled blood bank plasma and in the majority of apparently healthy donor plasmas. The spontaneous lysis of factor XII-deficient and prekallikrein-deficient plasmas was found to be similar to that of normal plasma. Addition of ellagic acid or antibodies against kallikrein or urokinase to normal pooled plasma did not alter significantly its rate of spontaneous lysis. On the other hand the addition of antibody against tissue activator (t-PA) inhibited over 80% of the spontaneous fibrinolysis in a 7-day incubation period at 37 degrees C, and the clot visually persisted for more than a month. Therefore, the factor XII-dependent components and prourokinase/urokinase system do not contribute significantly in whole plasma fibrinolysis in vitro, while the t-PA-related protein appears to be the major plasminogen activator responsible for initiating spontaneous fibrinolysis in whole plasma. Exogenous addition of increasing amounts of purified HeLa cell t-PA to normal pooled plasma in the ng/ml range cause progressively faster clot lysis. By extrapolation, normal pooled plasma is found to contain endogenous tissue activator in an amount functionally equivalent to 2 ng/ml of purified 60-kDa t-PA. The molecular nature of the t-PA-related proteins in plasma was studied by zymographic and immunological methods. The major t-PA-related protein in plasma was found to have a molecular mass of 100 kDa as determined by zymography. By incubating purified HeLa 60-kDa t-PA with a t-PA-depleted plasma, the 100-kDa component can be generated in plasma, suggesting that the latter is formed as a result of the binding of 60-kDa t-PA to a binding protein in plasma.