Down-regulation of Na(+)/K(+)-ATPase alpha(2) isoform in denervated rat vas deferens

The role of Na+/K+-ATPase during chick skeletal myogenesis

The formation of a vertebrate skeletal muscle fiber involves a series of sequential and interdependent events that occurs during embryogenesis. One of these events is myoblast fusion which has been widely studied, yet not completely understood. It was previously shown that during myoblast fusion there is an increase in the expression of Na⁺/K⁺-ATPase. This fact prompted us to search for a role of the enzyme during chick in vitro skeletal myogenesis. Chick myogenic cells were treated with the Na⁺/K⁺-ATPase inhibitor ouabain in four different concentrations (0.01-10 μM) and analyzed. Our results show that 0.01, 0.1 and 1 μM ouabain did not induce changes in cell viability, whereas 10 μM induced a 45% decrease. We also observed a reduction in the number and thickness of multinucleated myotubes and a decrease in the number of myoblasts after 10 μM ouabain treatment. We tested the involvement of MEK-ERK and p38 signaling pathways in the ouabain-induced effects during myogenesis, since both pathways have been associated with Na⁺/K⁺-ATPase. The MEK-ERK inhibitor U0126 alone did not alter cell viability and did not change ouabain effect. The p38 inhibitor SB202190 alone or together with 10 μM ouabain did not alter cell viability. Our results show that the 10 μM ouabain effects in myofiber formation do not involve the MEK-ERK or the p38 signaling pathways, and therefore are probably related to the pump activity function of the Na⁺/K⁺-ATPase.

Functionomics: the analysis of a postgenomic concept on the basis of pregenomic pharmacological studies in smooth muscle

The term functionomics (Amin 2003, Neumann et al. 2004) refers to a postgenomic integrated Systems Biology (Attur et al. 2002) using a multidimensional approach for cells, tissues and organs. It considers current or future involvement among genomics, proteomics or metabolomics, including the main factors that cause biological responses and modulation under different conditions. Our objective in the present review is to summarize the contemporary understanding of functionomics of smooth muscle pharmacology, based on the results obtained on the pregenomic era during several years in our laboratory. The present approach is based on the knowledge of the dynamics of the receptor system, which comprises a cascade of phenomena, leading from the drug administration to the final biological response. We will describe several conditions in which the final effect is modified, based on perturbations induced on drug absorption, distribution, metabolism, interaction with receptors and mobilization of second messengers, as well as by interactions with a second receptor system. We will also discuss the gaps that need to be fulfilled in order to obtain a clear and better understanding of the receptor system in smooth muscle, and to narrow the bridge between ourknowledge of the function of biological systems, genomics, and other recently introduced areas.

Mechanisms of adaptive supersensitivity in vas deferens

Adaptive supersensitivity is a phenomenon characteristic of excitable tissues and discloses as a compensatory adjustment of tissue's response to unrelated stimulatory endogenous and exogenous substances after chronic interruption of excitatory neurotransmission. The mechanisms underlying such higher postjunctional sensitivity have been postulated for a variety of cell types. In smooth muscles, especially the vas deferens with its rich sympathetic innervation, the mechanisms responsible for supersensitivity are partly understood and appear to be different from one species to another. The present review provides a general understanding of adaptive supersensitivity and emphasizes early and recent information about the putative mechanisms involved in this phenomenon in rodent vas deferens.

Adaptive expression pattern of different proteins involved in cellular calcium homeostasis in denervated rat vas deferens

The activity and protein expression of plasma membrane and sarco(endo)plasmic reticulum (Ca2+-Mg2+)ATPases and ryanodine receptors were investigated in surgically denervated rat vas deferens. The function of thapsigargin-sensitive but not thapsigargin-resistant (Ca2+-Mg2+)ATPase (from sarco(endo)plasmic reticulum and plasma membrane, respectively), evidenced by enzyme activity and Ca2+ uptake experiments, was significantly depressed by 30-50% when compared to innervated vas. Western blots showed that such reduction in sarco(endo)plasmic reticulum (Ca2+-Mg2+)ATPase performance was accompanied by a decrement of similar magnitude in sarco(endo)plasmic reticulum (Ca2+-Mg2+)ATPase type 2 protein expression, without any significant change in plasma membrane (Ca2+-Mg2+)ATPase expression. Finally, [3H]ryanodine binding revealed that the density of ryanodine binding sites was reduced by 45% after denervation without modification in affinity. The present findings demonstrate that sarco(endo)plasmic reticulum proteins involved in intracellular calcium homeostasis are clearly down-regulated and brings further evidence of a modified calcium translocation in denervated rat vas deferens.

Role of noradrenaline on the expression of the Na+/K+-ATPase alpha2 isoform and the contractility of cultured rat vas deferens

Rat vasa deferentia were cultured for 3 days in Dulbecco's modified Eagle's medium in the absence or presence of 1 microM noradrenaline (NA) to investigate if the lack of NA release is the key factor to explain the selective reduction of the Na(+)/K(+)-ATPase alpha(2) isoform previously observed after in vivo denervation of this organ (Quintas et al., Biochem Pharmacol 2000;60:741-7). The lack of effects of the indirect sympathomimetic tyramine and the neuronal amine uptake blocker cocaine on NA curves indicated that cultured organs were denervated completely. Organ culture induced supersensitivity, expressed as a 6.3-fold increase of pD(2) and a 42% elevation of maximal contraction for NA but not for Ba(2+). Western blotting indicated that the level of the alpha(1) isoform of Na(+)/K(+)-ATPase was unchanged after organ culture, but the alpha(2) isoform was down-regulated drastically to levels that were barely detectable. The addition of NA to the culture medium did not prevent the reduction of alpha(2) expression although it did impede NA supersensitivity (in fact a 4-fold decrease of pD(2) and a 32% reduction of maximal response were observed after incubation in the presence of NA). A striking reduction of L-type Ca(2+) channel expression also was observed, indicated by an 85% decrease of [3H]isradipine binding sites. These data suggest that NA is a trophic factor relevant to the control of muscle contraction, mediated by alpha(1)-adrenoceptors, but not to the expression of either Na(+)/K(+)-ATPase or the L-type Ca(2+) channel.