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Biomedical subjects

A L Steiner

Publications and source records attributed to A L Steiner.

At least 19 recordsLinked to original sources
PubMed1979

Characterization of rat testicular guanylate cyclase during development.

The biochemical characteristics of rat testicular guanylate cyclase were investigated and the activity and subcellular distribution of the enzyme was determined during testicular development. Examination of the effects of metal ions, nucleotides, detergents and other in vitro activators on the activity of guanylate cyclase revealed that the testicular enzyme is similar in most respects to guanylate cyclase isolated from other mammalian tissues. Changes in the total activity of guanylate cyclase during testicular development paralleled changes in the tissue concentration of cyclic GMP; i.e. guanylate cyclase activity and tissue cyclic GMP were highest during the early stages of development. Subcellular fractionation revealed that the activity of the soluble form of guanylate cyclase was best correlated with tissue cyclic GMP. Biochemical analysis of the soluble enzyme prepared from testes of neonatal and adult rats did not reveal any significant differences in the characteristics of the enzyme during ontogeny with the exception of a 2.5 fold increase in V noted in the neonatal testis. The results of this study are consistent with a molecular mechanism that allows independent regulation of the different forms of guanylate cyclase.

Adenosine Triphosphate↗
PubMed1979

Particulate guanylate cyclase of skeletal muscle: effects of Ca2+ and other divalent cations on enzyme activity.

The properties of particulate guanylate cyclase (GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2) from purified rabbit skeletal muscle membrane fragments were studied. Four membrane fractions were prepared by sucrose gradient centrifugation and the fractions characterized by analysis of marker enzymes. Guanylate cyclase activity was highest in the fraction possessing enzymatic properties typical of sarcolemma, while fractions enriched with sarcoplasmic reticulum had lower activities. In the presence of suboptimal Mn2+ concentrations, Mg2+ stimulated particulate guanylate cyclase activity both before and after solubilization in 1% Triton X-100. Guanylate cyclase activity was biphasic in the presence of Ca2+. Increasing the Ca2+ concentration from 10(-8) to 10(-5) M decreased the specific activity. As the Ca2+ concentration was further increased to 5 . 10(-4) M enzyme activity again increased. After solubilization of the membranes in 1% Triton X-100, Ca2+ suppressed enzyme activity. Studies utilizing ionophore X537A indicated that the altered effect of Ca2+ upon the solubilized membranes was independent of asymmetric distribution of Ca2+ and Mg2+.

Animals↗
PubMed1978

Association of cyclic GMP with gene expression of polytene chromosomes of Drosophila melanogaster.

The distribution of cyclic nucleotides on polytene chromosomes isolated from Drosophilia melanogaster salivary glands was examined by using an indirect immunofluorescent technique. With a fixative that minimized the loss of chromosomal proteins, cyclic GMP, but not cyclic AMP, was observed distributed along the chromosomes. The subchromosomal distribution of cyclic GMP correlated with genetically active sites on the chromosomes. After heat-shock treatments, the intensity of cyclic GMP fluorescence was markedly enhanced at specific loci on the chromosomes, with locus 93D as the most intensely fluorescent. Autoradiographic analysis with [3H]uridine revealed that 93D was the most transcriptionally active locus within a particular nucleus. These observations suggest that cyclic GMP may participate in processes associated with transcription on polytene chromosomes. The involvement of cyclic GMP in nuclear events associated with gene expression is discussed.

Animals↗
PubMed1978

Tissue guanosine-3',5'-cyclic monophosphate levels and soluble guanylate cyclase activity: a positive correlation during unilateral cryptorchidism in the rat testis.

The relationship between the subcellular distribution of guanylate cyclase and tissue guanosine-3',5'-cyclic monophosphate (cGMP) levels was investigated in rat testes after surgically induced unilateral cryptorchidism. Placement of one of a testis pair in the abdominal cavity results in loss of testicular weight and function in the abdominal testis whereas the remaining scrotal testis appears to be functionally normal. Within 5 days after surgery, tissue cGMP levels were increased by twofold in the abdominal testis. A fourfold elevation was noted from 10 to 30 days after surgery. Whereas the homogenate guanylate cyclase activity was only slightly elevated 10 and 20 days postoperatively, a 200% increase in the soluble guanylate cyclase activity was seen at 5 days. Between 10 and 30 days, the rise in activity was >250% (P < 0.01). An increase in soluble guanylate cyclase activity was noted when the data were expressed as per milligram protein, per milligram DNA or per whole testis. Conversely, particulate guanylate cyclase activity was reduced by 40% in the cryptorchid testis. Kinetic analysis of the soluble enzyme prepared from abdominal and scrotal testes yielded linear Line-weaver-Burke plots for both enzyme preparations with an identical K(m) for guanosine triphosphate, but a three-fold higher maximal velocity for the abdominal enzyme. When the soluble guanylate cyclases from both testes were mixed and assayed together, the activities were additive rather than exhibiting synergism or inhibition. These experiments indicate that the altered V(max) is not due to a transferable activator or inhibitor.An immunocytochemical technique was used to assess the cell type in which the alterations in cGMP metabolism occurred. Comparison of the scrotal and abdominal testes revealed that the abdominal testis exhibited enhanced cGMP immunofluorescence within the cells lining the inner aspect of the seminiferous tubule as well as tubular elements and interstitial cells. Thus, it is inferred that the correlated changes in soluble guanylate cyclase activity and cGMP levels occur in several of the cell types that remain viable within the cryptorchid testis.

Animals↗
PubMed1977

Lymphocyte surface modulation and cyclic nucleotides I. Topographic correlation of cyclic adenosine 3':5'-monophosphate and immunoglobulin immunofluorescence during lymphocyte capping.

The cross-linking of human peripheral lymphocyte surface Ig results in an early association of cyclic adenosine 3':5'-monophosphate (cAMP) and the cell surface Ig patches. Examination of the subsequent stages of cap formation reveals the continued relationship of cAMP and the clustered surface Ig. In addition, the generalized influx of calcium produced by the ionophore A-23187 disrupts human lymphocyte caps. During the process of cap dissolution cAMP is still associated with surface Ig. Therefore, it is hypothesized that the localized concentration of cyclic nucleotide and calcium ion regulates the movement of cell surface constituents by coordinating the function of the cell's contractile and structural elements.

Calcimycin↗
PubMed1977

Localization of cyclic GMP and cyclic AMP in cardiac and skeletal muscle: immunocytochemical demonstration.

When rat cardiac and skeletal muscle are explored by immunocytochemical procedures designed to show sites of localization of adenosine 3',5'-monophosphate (cyclic AMP) and guanosine 3',5'-monophosphate (cyclic GMP), distinct staining patterns for the two nucleotides are seen. Antibody to cyclic AMP is found in the area of the sarcoplasmic reticulum, while antibody to cyclic GMP is found with a periodic distribution corresponding to that of the A band. This suggests a role for cyclic GMP in the regulation of myosin.

Animals↗
PubMed1977

Regulation of hepatic nuclear guanylate cyclase.

In immunohistochemical studies of rat liver tissue slices and purified nuclei, adenosine 3':5'-cyclic monophosphate (cAMP) and guanosine 3':5'-cyclic monophosphate (cGMP) immunofluorescence on the nuclear membrane are sequentially increased after glucagon administration. An explanation for the increased cGMP immunofluorescence was sought in experiments in which guanylate cyclase [GTP pyrophosphate-lyase (cyclizing), EC 4.6.1.2]activity of hepatic subcellular fractions was determined. The results showed that a nuclear guanylate cyclase exists which can be distinguished from the soluble and crude particulate guanylate cyclases. The activity of the nuclear enzyme was increased by 35% in nuclei isolated from rats 30 min after glucagon injection, the time at which maximal nuclear membrane cGMP immunofluorescence is observed. Because glucagon altered both cAMP location and levels prior to the observed changes in nuclear cGMP metabolism, the hypothesis that cAMP acted as the second messenger was tested. In vitro incubation of nuclei isolated from control rats with 10(-5) M cAMP produced a 25% increase in nuclear guanylate cyclase activity. With nuclei isolated from glucagon-treated rats, no significant increase in enzyme activity was observed; this indicates that maximal stimulation of nuclear guanylate cyclase by cAMP occurred at levels that are obtained in vivo after glucagon administration. These findings suggest that hepatic nuclear cGMP content may be regulated by a specific organelle guanylate cyclase and that cAMP may be one of the determinants of this enzyme's activity.

Animals↗
PubMed1977

Immunohistochemical localization of 3':5'-cyclic AMP and 3':5'-cyclic GMP in rat renal cortex: effect of parathyroid hormone.

Adenosine 3':5'-cyclic monophosphate (cAMP) and guanosine 3':5'-cyclic monophosphate (cGMP) were localized in cells of rat kidney cortex by an immunocytochemical technique before and after perfusion with parathyroid hormone (PTH). In control tissues the cAMP antiserum detected approximately the same intensity of fluorescence in cytoplasmic epithelial cell elements of cortical tubules and glomeruli (cells of Bowman's capsule and podocytes). PTH increased fluorescence in these glomerular cells and increased cAMP fluorescence in cytoplasmic granules in proximal tubular cells. These granules, whose structure has not been identified, were located predominantly on the luminal side of the tubular cells. In control rats, the renal cortical fluorescence detected with the cGMP antiserum was more pronounced in glomeruli (predominantly in the mesangial areas) and lesser amounts of fluorescence were observed in tubules. After PTH treatment, cGMP fluorescence increased in glomeruli and in renal tubular cells. A bright linear pattern of fluorescence was found in the area of the tubular luminal membrane. Perfusion with PTH caused relatively small increases in total tissue cAMP and no consistent increases in total tissue cGMP. Our observations suggest that both cAMP and cGMP are involved in the glomerular and tubular responses to PTH and point out the added dimension that this immunocytochemical technique brings to studies of cyclic nucleotide dynamics in heterogeneous tissues.

Animals↗
PubMed1976

Effect of angiotensin II on cyclic guanosine monophosphate and cyclic adenosine monophosphate in human plasma.

Infusion of alpha-adrenergic catecholamines increases plasma cyclic guanosine monophosphate (pcGMP), raising the possibility that the pressor effect of these agents may be mediated by cyclic GMP. We infused pressor doses of angiotensin II in 10 studies in 8 normal subject and measured pcGMP and plasma cyclic adenosine monophosphate (pcAMP) by radioimmunoassay. After 120 minutes of infusion, mean pcGMP was 128 +/- 31% (SE) higher than baseline values (P less than 0.01) while pcAMP was increased 30 +/- 10% (P less than 0.05).

Angiotensin II↗
PubMed1976

Cyclic nucleotides in pancreatic islets. Tolbutamide- and arginine-induced insulin release.

With the use of isolated rat islet perfusion, levels of the islet cyclic adenosine 3' ,5' -monophosphate (cAMP) were compared with dynamic insulin secretion induced by tolbutamide and arginine. Tolbutamide elevated islet cAMP rapidly and augmented both glucose-induced islet cAMP levels and insulin secretion; arginine, however, did not elevate islet cAMP but did enhance glucose-induced insulin secretion. Since the latter result could have been modulated by cyclic guanosine 3' ,5' -monophosphate, this cyclic nucleotide was also measured and found to remain unchanged during stimulation of insulin secretion by arginine and a combination or arginine and glucose. Thus, the action of tolbutamide appears to be modulated in part by cAMP, whereas arginine appears to augment insulin secretion independently of cyclic nucleotides.

Animals↗
PubMed1975

Neurotransmitters increase cyclic nucleotides in postganglionic neurons: immunocytochemical demonstration.

Dopamine increases adenosine 3',5'-monophosphate (cyclic AMP) but not guanosine 3',5'-monophosphate (cyclic GMP) in slices of bovine sympathetic ganglion; this increase is localized to the postganglionic neurons. Conversely, acetylcholine increases cyclic GMP but not cycle AMP in the ganglion; this increase also occurs within postganglionic neurons. Thus, different neurotransmitters can selectively alter cyclic nucleotide levels within the same neuronal population.

Acetylcholine↗