Search PubMed⌕ Search

Biomedical subjects

R A Janis

Publications and source records attributed to R A Janis.

52 records · Page 3Linked to original sources
PubMed1977

Alterations in calcium transport and binding by the plasma membrane of mesenteric arteries from spontaneously hypertensive rats.

The effect of Sr++, Ba++ and Mn++ on calcium uptake by a plasma membrane-enriched fraction from mesenteric arteries of spontaneously hypertensive rats (SHR) was studied to determine what alterations in divalent cation interactions are associated with hypertension. 45Ca++ uptake in the presence of ATP by this fraction from SHR was significantly greater than that of normotensive rats (NWR). This 45Ca++ uptake by these fractions from both types of rat could be reduced by Ba++, Sr++ and nonradioactive Ca++, but not by Mn++; the ability of these cations to compete with 45Ca++ was in the following order Ca++ greater than Sr++ greater than Ba++. In contrast, 45Ca++ uptake in the absence of ATP by this subcellular fraction from SHR was significantly less than that of NWR, and this passive 45Ca++ binding could be displaced by Mn++ in addition to the other cations. Both qualitative and quantitative differences were found between SHR and NWR in this study of the effects of cations on calcium uptake by arterial plasma membrane. These results suggest that the plasma membrane of SHR arteries has calcium-binding and transport properties that are different from those of NWR. However, there is not a complete correlation between the reported effects of the cations on contraction of other arteries in hypertension and on calcium uptake by membranes of SHR and NWR.

Adenosine Triphosphate↗
PubMed1977

Relationship between blood pressure of spontaneously hypertensive rats and alterations in membrane properties of mesenteric arteries.

Spontaneously hypertensive rats (SHR) and two strains of normotensive rats were compared with respect to enzymatic activities and calcium accumulation of plasma membrane and endoplasmic reticulum enriched fractions from their mesenteric arteries. Increased specific activities of alkaline phosphatase, 5'-nucleotidase and Mg2+-ATPase, and increased ATP-dependent calcium accumulation were found in 5- to 6-month-old SHR as compared to both strains fo age-matched normotensive rats. Alkaline phosphatase was increased in 33-day-old "early hypertensive" and 3- to 4-month-old SHR, but 5'-nucleotidase, Mg2+-ATPase, and calcium accumulation were not. Hydralazine treatment of young SHR partially prevented the increase of both alkaline phosphatase activity and blood pressure that develops with age. The relationship between alkaline phosphatase activity and the alterations in vascular reactivity associated with hypertension remains to be determined.

Adenosine Triphosphatases↗
PubMed1976

The role of sarcolemma and mitochondria in regulating Ca2+ movements in human myometrium.

A subcellular fraction enriched in sarcolemma was isolated by differential and sucrose gradient centrifugation from human myometrium. The Ca2+ binding characteristics of this fraction were compared to that of mitochondria and microsomes that were isolated simultaneously. 1. Oxalate increased ATP-dependent Ca2+ uptake by the sarcolemmal but not the mitochondrial fraction, while azide inhibited mitochondrial but not sarcolemmanl Ca2+ transport. 2. The amount of Ca2+ bound in 10 min by these two fractions from a 0.3 muM free Ca2+ solution was similar, but the rate of Ca2+ uptake at 1 muM Ca2+ was greater for the mitochondrial than the sarcolemmal. fraction. The properties of Ca2+ binding by the microsomal fraction were intermediate between these two fractions. 3. The results suggest that mitochondria have a greater potential for lowering intracellular Ca2+ activity in human myometrium than do sarcolemma or sarcoplasmic reticulum.

Adult↗
PubMed1976

Isolation and characterization of plasma membrane from rat mesenteric arteries.

A method for isolating a plasma membrane-enriched fraction and other subcellular fractions from rat mesenteric arteries by the use of a discontinuous sucrose density gradient is decribed. Electron microscopy showed both plasma membrane and endoplasmic reticulum fractions to be composed of vesicles. 5'-Nucleotidase, alkaline phosphatase, ouabain-sensitive (Na+ + K+)-ATPase and K+-phosphatase, and phosphodiesterase I were concentrated in the plasma membrane fraction. The increase in ATP-dependent calcium uptake in the presence of oxalate was greater in the endoplasmic reticulum than in the plasma membrane fraction. The lack of inhibition of active calcium uptake by azide suggests that the plasma membrane-enriched fraction was relatively free of mitochondrial contamination. Calcium uptake by the plasma membrane or the endoplasmic reticulum fraction was not enhanced by high-energy compounds other than ATP, and was little affected by 100 mM KCl or NaCl in the Mg++-containing medium. Subcellular fractions isolated by this method will be useful for investigating the biochemistry of small blood vessels of the rat.

Acid Phosphatase↗
PubMed1976

Calcium accumulation and enzymatic activities of subcellular fractions from aortas and ventricles of genetically hypertensive rats.

Subcellular fractions were obtained from aortas and ventricles of 6-month-old spontaneously hypertensive and normotensive Wistar rats by the use of differential and sucrose density gradient centrifugation. These preparations were studied to determine what alterations in calcium accumulation and enzymatic activities might be associated with hypertension. The total amount of calcium accumulation (in the presence of ATP and 17 muM free calcium) by the plasma membrane-enriched fraction from hypertensive rat aortas significantly less than that from normotensive rats (11.3 +/- 0.4 vs 16.2 +/- 1.6 mumol of calcium/g of protein, n = 8). In contrast the specific activities of the plasma membrane marker enzymes, 5'-nucleotidase and phosphodiesterase I, were 80% and 40% greater, respectively, in the hypertensive than in the normotensive fractions. On the other hand, various fractions from ventricles of the two types of rats were generally similar in enzyme activities and calcium accumulation. The decreased rate of relaxation of aortas from spontaneously hypertensive rats may be caused by the decreased rate of calcium transport demonstrated in this study.

Animals↗
PubMedDate not supplied

BAY K 8644-induced enhancement of 45Ca uptake by rabbit aortic rings.

BAY K 8644, a Ca2+ channel activator, enhances uptake of 45Ca by rabbit aortic rings. This effect depends on the concentration of K+ in the medium: at 20 mM K+ the effect of BAY K 8644 was more pronounced than at 5 mM, whereas at 80 mM, no significant enhancement of 45Ca uptake by BAY K 8644 was found. In the medium containing 5 mM K+, BAY K 8644 was effective in experiments involving 10 or 30 (but not 3) min exposure of aortic rings to 45Ca. The dose-response curve for BAY K 8644 was established in 5 mM K+-containing medium and for 30 min exposure to 45Ca. BAY K 8644 was effective at 0.01 microM and higher concentrations. In the presence of norepinephrine (0.1 or 10 microM), BAY K 8644 had no greater effect on 45Ca uptake than in control 5 mM K+ medium. Our observation that the presence of norepinephrine in 5 mM K+ did not enhance BAY K 8644-induced 45Ca uptake suggests that activation of alpha-adrenergic receptor does not depolarize aortic membranes to the same extent as an increase in K+ concentration to 20 mM or that BAY K 8644 does not enhance Ca2+ entry through receptor-operated channels.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗