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Biomedical subjects

S Mackie

Publications and source records attributed to S Mackie.

13 recordsLinked to original sources
PubMed1997

Multiple modes of activation of the stress-responsive MAP kinase pathway in fission yeast.

The Schizosaccharomyces pombe wis1(+) gene is essential for cell survival under stress conditions. The MAPKK homologue Wis1 is required for activation of the MAPK homologue Spc1, and integrity of the Wis1-Spc1 pathway is required for survival in extreme conditions of heat, osmolarity, oxidation or limited nutrition. We show here that Wis4, a protein kinase of a new MAPKKK class, phosphorylates Wis1 in vitro and activates it in vivo. Win1 is also required for full activation of Wis1, and Win1 rather than Wis4 mediates the osmotic stress signal. Surprisingly, the pathway can still be activated by heat or oxidative stress independently of the phosphorylation of two conserved Wis1 residues. Evidence is presented that the Pyp1 protein tyrosine phosphatase, which dephosphorylates Spc1, is central to this alternative activation mechanism.

Amino Acid Sequence↗
PubMed1996

The wis1 signal transduction pathway is required for expression of cAMP-repressed genes in fission yeast.

The wis1 protein kinase of Schizosaccharomyces pombe is a member of the MAP kinase kinase family. Loss of wis1 function has previously been reported to lead to a delay in the G2-mitosis transition, loss of viability in stationary phase, and hypersensitivity to osmotic shock. It acts at least in part by activating the MAP kinase homologue sty1; loss-of-function sty1 mutants share many phenotypes with wis1 deletion mutants. We show here that, in addition, loss of wis1 function leads to defective conjugation, and to suppression of the hyperconjugation phenotype of the pat1-114 mutation. Consistent with this, the induction of the mei2 gene, which is normally induced by nitrogen starvation, is defective in wis1 mutants. In wild-type cells, nitrogen starvation leads to mei2 induction through a fall in intracellular cyclic AMP (cAMP) level and activity of the cAMP-dependent protein kinase. We show here that wis1 function is required for mei2 induction following nitrogen starvation. Expression of the fbp1 gene is negatively regulated by cAMP in response to glucose limitation: induction of fbp1 also requires wis1 and sty1 function. Loss of wis1 is epistatic over increased fbp1 expression brought about by loss of adenylate cyclase (git2/cyr1) or cAMP-dependent protein kinase (pka1) function. These observations can be explained by a model in which the pka1 pathway negatively regulates the wis1 pathway, or the two pathways might act independently on downstream targets. The latter explanation is supported, at least as regards regulation of cell division, by the observation that loss of function of the regulatory subunit of the cAMP-dependent protein kinase (cgs1) brings about a modest increase in cell length at division in both wis1+ and wis1 delta genetic backgrounds.

Cyclic AMP↗
PubMed1992

Clinical, pathologic, and biochemical features of a cholesterol lipidosis accompanied by hyperlipidemia and xanthomas.

We describe the unique clinical and histopathologic features of a child with biochemical and immunocytochemical features of Niemann-Pick disease type C (NPC). Clinically, she was found to have multiple xanthomas of the upper aerodigestive tract with dysphagia and expressive language delay, splenomegaly, bony infarcts, and type IIb hyperlipidemia. Neurologic examination was otherwise normal. Microscopy revealed foam cells in her bone marrow, liver, tongue, tonsils, glottis, and in normal-appearing peritonsillar mucosa. Lipid analysis of a liver biopsy specimen showed a small increase in phospholipids, a twofold increase in sphingomyelin, a fivefold increase in cholesterol, and a marked (25-fold) increase in bis(monoacylglycerol) phosphate. Lysosomal acid hydrolase activities in cultured skin fibroblasts were nondiagnostic. Biochemical and immunocytochemical studies of cultured fibroblasts demonstrated lysosomal accumulation of unesterified LDL-derived cholesterol as well as delayed induction of homeostatic responses to endogenous cholesterol consistent with a diagnosis of NPC. Based upon these observations, we speculate that this patient could have a new phenotypic expression of NPC or represents a new cholesterol lipidosis biochemically resembling NPC. The chance occurrence of two separate lipid disorders seems less likely.

Biopsy↗
PubMed1991

Hemoglobin aggregation and pseudosickling in vitro of hemoglobin Setif-containing erythrocytes.

Erythrocytes from individuals heterozygous for hemoglobin Setif (alpha 94 Asp----Tyr) sickle in vitro without deoxygenation when incubated in chloride buffer due to hemoglobin aggregation. We now report quantitative studies of hemoglobin polymerization and deformability in these cells. Hemoglobin polymer gradually increased in intact cells during a 24 h incubation period at 24 degrees C. After 24 hr, about 80% of the cells in 290 mOsm sodium chloride buffer contained polymer which appeared as short rods compared to greater than 99% containing polymer at 450 mOsm. Similar proportions of cells were morphologically sickled. Deformability of erythrocytes with 40% hemoglobin Setif incubated in 290 mOsm buffer at 37 degrees C decreased to 80% of normal by 210 min but in 450 mOsm decreased to 50% after only 30 min as measured by the ektacytometer. However, at 4 degrees C deformability remained normal even in 450 mOsm buffer. The solubility of gelled hemolysate containing 40% hemoglobin Setif was 24 g/dl and 21 g/dl at 290 and 459 mOsm buffer respectively. The gel persisted at 4 degrees C with a solubility of 26 g/dl, but melted when dialyzed into sodium phosphate or potassium phosphate buffer. These data suggest that hemoglobin polymerization, reduced deformability, and sickling of hemoglobin Setif-containing erythrocytes are related to reduced hemoglobin solubility. The rate and extent of intracellular polymerization in vitro are considerably reduced (as in the case of sickle trait) compared with erythrocytes from individuals with sickle cell anemia. Hence, the slower kinetics of hemoglobin aggregation in hemoglobin Setif-containing cells provide an alternate system for studying hemoglobin polymerization and abnormal rheology.

Anemia, Sickle Cell↗
PubMed1989

The role of cyclin synthesis, modification and destruction in the control of cell division.

This paper reviews our current knowledge of the cyclins based on observations of the oocytes and eggs of sea urchins, clams and frogs. Cyclins are proteins found in all eukaryotes whose special property is rapid destruction at specific stages in the cell cycle. The cyclins fall into three families. A-type cyclins have been found in clams, flies and frogs. B-type cyclins have been found in clams, flies, frogs, sea urchins and fission yeast. A more distantly related family of three genes is found in Saccharomyces cerevisiae. B-type cyclins appear to be required for cells to enter mitosis, and their destruction is thought to be necessary for exit from mitosis. We describe evidence in support of these ideas, and describe various conditions under which cyclin destruction is delayed or deranged. We conclude with a discussion of the relationship between the cyclins and maturation- (or M phase-) promoting factor and some ideas on how the cyclins may work.

Animals↗
PubMed1984

Renal tubular acidosis induced by dietary chloride.

Previous studies have demonstrated that dietary intake of anions with high renal reabsorbability (Cl- greater than SO4=) can result in either exacerbation of chronic metabolic acidosis or correction of chronic metabolic alkalosis. These results, however, fail to predict the renal acid-base response to Cl- administration when systemic acid-base composition is initially normal, but accompanied by an extracellular fluid (ECF) volume-mediated renal avidity for Cl- reabsorption; that is, the renal options include HCl retention, KCl retention, and phosphaturia. Accordingly, the present metabolic balance studies evaluated the response to substitution of dietary Cl- (2.5 mEq/kg/day) for Pi in five dogs previously ECF-depleted with diuretics and maintained on a dietary K+ supplement, 5.0 mEq/kg daily as neutral Pi (electrolyte-free diet) during a steady-state control period. Dietary Cl- resulted in a decrease in arterial plasma [HCO3-] from 21.2 +/- 0.7 to 17.8 +/- 0.8 mEq/liter, (P less than 0.01) and increase in [H+] from 38.5 +/- 0.7 to 43.3 +/- 0.8 nEq/liter (P less than 0.001). Urine pH increased (P less than 0.01), the cumulative change in net acid excretion decreased (-79 mEq, P less than 0.05), and Cl- retention (39 mEq, P less than 0.05) occurred. No change in Na+, K+, or Pi excretion occurred. The renal acidosis was fully corrected when SO4= was substituted for dietary Cl- and redeveloped when Cl- was resubstituted . Superimposition of a large oral buffer load (creatinine) did not ameliorate Cl- -induced renal acidosis. The results indicate that dietary reabsorbable anions can result in renal acidosis when Cl- reabsorption is stimulated and suggest that anion reabsorbability characteristics and not anion buffer properties are responsible.

Acid-Base Equilibrium↗
PubMed1984

Effect of extracellular fluid volume depletion on renal regulation of acid-base and potassium equilibrium during prolonged mineral acid administration.

Previous studies of the renal and systemic acid-base response to prolonged administration of mineral acids in dogs have suggested that during the steady state of acidosis, the level at which plasma bicarbonate concentration is regulated by the kidney is dependent on the degree of augmentation of "distal delivery" of sodium imposed by the increased filtered load of administered mineral acid anion with filtered sodium, and on the degree of augmentation of "distal avidity" for sodium reabsorption imposed by ECF volume ( ECFV ) contraction secondary to renal sodium losses accompanying the administered mineral acid anion. This formulation, however, fails to predict the level at which plasma bicarbonate concentration would be regulated under conditions of preexisting ECFV depletion, which would simultaneously limit distal delivery of sodium salts and yet increase distal avidity for sodium reabsorption. Our studies assessed the renal and systemic acid-base responses to prolonged daily administration of 5.0 mEq/kg of H+ as HCl (groups 1 and 2) or H2SO4 (groups 3 and 4) in dogs with normal ECFV (groups 1 and 3) vs. preexisting ECFV depletion (groups 2 and 4) induced by administration of ethacrynic acid. In response to HCl administration, dogs with depleted ECFV developed more severe acidosis than ECFV -replete dogs (delta[HCO-3,]p, -5.0 +/- 0.6 mEq/L, group 2 vs. -2.7 +/- 0.5 mEq/L, group 1, p less than 0.02). The exacerbated metabolic acidosis in group 2 persisted in the steady state, even though the steady-state net systemic acid load was not greater than in group 1. No exacerbation of acidosis was observed in H2SO4-fed dogs with depleted ECFV . In response to either HCl or H2SO4, persistent hypokalemia caused by increased renal potassium clearance occurred in ECFV -replete dogs but not in ECFV -depleted dogs. Our results indicate that preexisting ECFV depletion results in impaired renal hydrogen ion secretion during prolonged HCl feeding, but not during H2SO4 feeding. These results suggest that during prolonged HCl loading under conditions of preexisting ECFV depletion, hypovolemia-mediated restriction of the normal augmentation of distal delivery of sodium salts overrides the effects of enhanced distal cation secretory capacity that attends hypovolemia-mediated augmentation of distal avidity for sodium reabsorption.

Acid-Base Equilibrium↗
PubMed1984

Thyroid replacement in thyroparathyroidectomized dogs.

The thyroparathyroidectomized dog is an important experimental model of hypoparathyroidism and has been widely utilized for acute and chronic studies of the physiologic role of parathyroid hormone on systemic and renal acid-base, electrolyte and vitamin D physiology. Despite widespread use of this model, the appropriate thyroid hormone replacement dose necessary for achievement of postoperative euthyroidism has not been established for this species. Accordingly, serum thyroxine (T4) concentration was measured prior to and following chronic thyroparathyroidectomy in dogs given thyroid hormone replacement at different doses and routes of administration: sodium levothyroxine, 2.4 micrograms/kg daily in one or two divided subcutaneous doses (group I, n = 9), 20 micrograms/kg daily in two divided oral doses (group II, n = 8), and a wide range of intravenous doses (group III, n = 3). Group I dosage was based on the reported T4 production rate in dogs and is slightly greater than the reported production rate in man. Group II dosage was based on published clinically derived estimates of required replacement amounts. With subcutaneous replacement (group I) serum T4 concentration decreased from a preoperative value of 1.80 +/- 0.20 to 0.60 +/- 0.10 microgram/100 ml (p less than 0.001) following thyroparathyroidectomy. With oral replacement (group II), serum T4 concentration after thyroparathyroidectomy was not significantly changed from control (1.88 +/- 0.22 vs. 1.66 +/- 0.43 microgram/100 ml). Group III studies revealed that both total and free serum T4 concentration could be normalized after thyroparathyroidectomy with an intravenous dose of 10 micrograms/kg daily. As found with subcutaneous administration, intravenous replacement with lesser amounts of T4 than 10 micrograms/kg daily (i.e. 2.5 micrograms/kg) resulted in significant decreases in serum T4 concentration from control.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1983

Controlled trial of propranolol for the prevention of recurrent variceal hemorrhage in patients with cirrhosis.

We conducted a prospective randomized trial of propranolol for the prevention of recurrent variceal bleeding in 48 patients with cirrhosis of the liver. During a follow-up period of up to 21 months, 12 of 26 patients in the propranolol group and 11 of 22 in the control group had rebleeding from esophageal varices. There was no significant difference in rebleeding between the two groups. This contrasts with a previous report of the efficacy of propranolol in preventing recurrent gastrointestinal bleeding in alcoholic cirrhosis. The difference in results may be due to the inclusion in our study of patients with other causes of cirrhosis and more severe liver disease. Propranolol may not be indicated for the prophylaxis of variceal rebleeding in such patients, and we advocate that its use be limited at present to controlled clinical trials.

Adult↗
PubMed1983

The effect of ranitidine on the plasma clearance and hepatic extraction of indocyanine green in patients with chronic liver disease.

Since hepatic clearance of ICG is reduced by H2-receptor antagonists in normal subjects, it has been suggested that they reduce liver blood flow. We have studied the effect of intravenous ranitidine on ICG clearance in twelve patients with chronic liver disease. Wedged and free hepatic venous pressure were measured before and after intravenous ranitidine in nine of the patients, and the hepatic extraction of ICG was determined in six patients. ICG clearance fell by 22 +/- 11% (s.e. mean) 60 min after ranitidine. In patients in whom ICG clearance fell after intravenous ranitidine the hepatic extraction of ICG was also reduced. There was no significant change in the gradient between wedged and free hepatic venous pressure after ranitidine. It is therefore unlikely that ranitidine lowers liver blood flow.

Adolescent↗
PubMed1982

Effect of low potassium-diet on Na-K-ATPase in rat nephron segments.

Na-K-ATPase activity was determined in 10 segments of the rat nephron using a fluorometric microassay method [4]. The enzyme activity showed three peaks (greater than 200 pmol ADP min-1 mm-1) along the nephron of normal rats. These peaks were in the S1 portion of the proximal tubule, the medullary thick ascending limb from the inner stripe and the distal convoluted tubule. Feeding the rats a low potassium diet for 8 weeks produced a significant decrease in Na-K-ATPase activity in the cortical collecting duct, but no significant change in this enzyme in any other segment. The low potassium diet did not produce a significant change in Mg-ATPase in any nephron segments. We conclude that Na-K-ATPase activity along the rat nephron shows a pattern that is qualitatively similar to that seen in the rabbit nephron [4]. However, quantitatively the Na-K-ATPase activity in the rat nephron is greater than in the corresponding segments of the rabbit nephron. The results are consistent with the greater rate of glomerular filtration and Na+ reabsorption per rat nephron. Furthermore, our results suggest that the decrease in potassium excretion during potassium deficiency is modulated, at least in part, by the level of Na-K-ATPase activity in the cortical collecting duct.

Absorption↗