Modulation of rhodopsin gene expression and signaling mechanisms evoked by endothelins in goldfish and murine pigment cell lines

Endothelins (ETs) and sarafotoxins (SRTXs) belong to a family of vasoconstrictor peptides, which regulate pigment migration and/or production in vertebrate pigment cells. The teleost Carassius auratus erythrophoroma cell line, GEM-81, and Mus musculus B16 melanocytes express rhodopsin, as well as the ET receptors, ETB and ETA, respectively. Both cell lines are photoresponsive, and respond to light with a decreased proliferation rate. For B16, the doubling time of cells kept in 14-h light (14L):10-h darkness (10D) was higher compared to 10L:14D, or to DD. The doubling time of cells kept in 10L:14D was also higher compared to DD. Using real-time PCR, we demonstrated that SRTX S6c (12-h treatment, 100 pM and 1 nM; 24-h treatment, 1 nM) and ET-1 (12-h treatment, 10 and 100 pM; 24- and 48-h treatments, 100 pM) increased rhodopsin mRNA levels in GEM-81 and B16 cells, respectively. This modulation involves protein kinase C (PKC) and the mitogen-activated protein kinase cascade in GEM-81 cells, and phospholipase C, Ca2+, calmodulin, a Ca2+/calmodulin-dependent kinase, and PKC in B16 cells. Cells were kept under constant darkness throughout the gene expression experiments. These results show that rhodopsin mRNA levels can be modulated by SRTXs/ETs in vertebrate pigment cells. It is possible that SRTX S6c binding to the ETB receptors in GEM-81 cells, and ET-1 binding to ETA receptors in B16 melanocytes, although activating diverse intracellular signaling mechanisms, mobilize transcription factors such as c-Fos, c-Jun, c-Myc, and neural retina leucine zipper protein. These activated transcription factors may be involved in the positive regulation of rhodopsin mRNA levels in these cell lines.

Papel de los mediadores vasoactivos en la fisiopatología de la hipertensión portal / Role of vasoactive mediators in the physiopathology of portal hypertension

Se evalúa el papel de los mediadores vasoactivos en la fisiopatología de la hipertensión portal, ya sea promoviendo un aumento de la resistencia vascular en la circulación intrahepática y/o portocolateral, o estimulando una vasodilatación esplácnica con un paralelo incremento del flujo sanguíneo portocolateral. En la actualidad se conoce que el factor inicial de la hipertensión portal es el aumento de la resistencia vascular intrahepática, ocasionada por los cambios morfológicos del hígado asociados a la cirrosis. Sin embargo, existen en la actualidad múltiples evidencias sobre la participación de un componente activo, células con propiedades contráctiles, que puede ser modulado por mediadores vasoactivos como la endotelina y el óxido nítrico. Por otra parte, se conoce actualmente que el aumento del flujo sanguíneo portal mantiene y agrava el síndrome de hipertensión portal. Este aumento del flujo portal es el resultado de una vasodilatación esplácnica ocasionada tanto por el aumento de sustancias vasodilatadoras como por una hiporreactividad a vasoconstrictores endógenos. En este sentido, estudios clínicos y experimentales han demostrado que sustancias como el glucagon, la prostaciclina y más recientemente el óxido nítrico, pueden jugar un papel importante en ambos mecanismos de vasodilatación esplácnica

The effect of lovastatin on proliferation of cultured rat mesangial and aortic smooth muscle cells

In order to investigate the anti-proliferative effect of 3-hydroxy-3-methylglutaryl coenzyme. A reductase inhibitor, we evaluated the effects of lovastatin on DNA replication and the proliferation of rat mesangial and aortic smooth muscle cells, both of which were mesenchymal origin cells. Proliferations were determined by measuring [3H]thymidine uptake, and counting the number of cells. Growth-arrested mesangial and aortic smooth muscle cells were exposed to platelet-derived growth factor (PDGF), endothelin (ET) and angiotensin II (Ang II) to stimulate mitogenesis. All agents exhibited dose-dependent stimulation of [3H] thymidine uptake. PDGF was more potent than the others. Ang II increased [3H] thymidine uptake without demonstrable mitogenic activity. Lovastatin inhibited PDGF (10 ng/ml in mesangial cell, 25 ng/ml in smooth muscle cell)-, ET (10(-7)M)- and Ang II (10(-7)M)-induced [3H] thymidine uptake significantly in a dose-dependent manner in both cells. The increase of cell number in response to PDGF and ET treatment were also inhibited at 10 microM of lovastatin. The inhibitory effect of lovastatin was largely overcome in the presence of exogenous mevalonate at 200 microM, with 75.5% restoration from lovastatin-induced inhibition on PDGF-induced [3H] thymidine uptake in mesangial cells (77.8% in aortic smooth muscle cells). However, the addition of cholesterol did not prevent inhibition by lovastatin. In conclusion, lovastatin had an inhibitory effect on mesangial and aortic smooth muscle cell proliferation, and mevalonate was essential for DNA replication in both types of cells. Lovastatin may reduce glomerular and atherosclerotic injury through an anti-proliferative effect on mesangial and vascular smooth muscle cells, in addition to lowering circulating lipids.

Endothelin-1 and carbachol: differences in contractile effects and myosin phosphorylation in lamb tracheal smooth muscle.

Endothelin-1 is a new potent vasoconstrictor peptide produced by the endothelial cells. The contractile effects of endothelin-1 (ET-1) were compared with those of cabachol in lamb tracheal smooth muscle. Equimolar concentrations (10(-6)M) of endothelin 1 and carbachol elicit rapidly rising isometric tension which is maintained indefinitely in a steady state when fibres are stimulated with carbachol. Fibre strips exposed to ET-1 cannot maintain peak isometric force beyond 15-20 min and instead these exhibit a decline in tension towards near relaxed state. In addition to an early transient relaxation, ET-1 stimulation results in a 20,000 Da myosin light chain phosphorylation pattern different from that of carbachol stimulation.

Endothelin-1 and okadaic acid induced contractions in tracheal smooth muscle of lamb.

Stimulation of lamb tracheal smooth muscle fibre strips with endothelin-1 and okadaic acid results in the development of isometric tensions which are long lasting. However, endothelin-1 is more potent constrictor than okadaic acid. An analysis of 20,000 Da regulatory myosin light chain by two-dimensional gel electrophoresis shows an identical phosphorylation pattern.

Reversal of endothelin-1-induced contractions by isoproterenol without myosin dephosphorylation in tracheal smooth muscle.

Effects of isoproterenol on isometric force, and 20,000 Da myosin light chain (LC20) phosphorylation were examined in smooth muscle fibre strips from lamb trachea stimulated with endothelin-1 (ET-1). ET-1 induced a rapidly rising isometric tension which was coupled with a multiple site phosphorylation of LC20. Isoproterenol addition at the time of peak isometric force resulted in a brisk relaxation of the fibre strips. Myosin light chain phosphorylation, however, remained unaffected.