Micrococcus luteus -- survival in amber.

A growing body of evidence now supports the isolation of microorganisms from ancient materials. However, questions about the stringency of extraction methods and the genetic relatedness of isolated organisms to their closest living relatives continue to challenge the authenticity of these ancient life forms. Previous studies have successfully isolated a number of spore-forming bacteria from organic and inorganic deposits of considerable age whose survival is explained by their ability to enter suspended animation for extended periods of time. However, despite a number of putative reports, the isolation of non-spore-forming bacteria and an explanation for their survival have remained enigmatic. Here we describe the isolation of non-spore-forming cocci from a 120-million-year-old block of amber, which by genetic, morphological, and biochemical analyses are identified as belonging to the bacterial species Micrococcus luteus. Although comparison of 16S rRNA sequences from the ancient isolates with their modern counterparts is unable to confirm the precise age of these bacteria, we demonstrate, using complementary molecular and cell biological techniques, evidence supporting the view that these (and related modern members of the genus) have numerous adaptations for survival in extreme, nutrient-poor environments, traits that will assist in this bacteria's persistence and dispersal in the environment. The bacteria's ability to utilize succinic acid and process terpine-related compounds, both major components of natural amber, support its survival in this oligotrophic environment.

Thrombin stimulates atrial natriuretic peptide secretion from rat cardiac atrium.

Atrial natriuretic peptide (ANP) is a hormone secreted predominantly by atrial myocytes. Although atrial distension is the primary stimulus of ANP secretion, several hormones have also been implicated in the regulation of ANP secretion. alpha-Thrombin, a serine protease participating in the blood coagulation system, has additional hormone-like effects in several cell types, apparently via interaction with specific cell surface receptors. Here we report that alpha-thrombin enhanced ANP secretion from isolated rat atrium within 10 min, in a concentration-dependent manner. The protease also significantly increased ANP release from cultured atrial myocytes, in a concentration-dependent manner. The alpha-thrombin-induced release of ANP from cultured atrial myocytes was completely abolished by hirudin, a specific alpha-thrombin protease inhibitor. Furthermore, synthetic peptides, identical in their amino acid sequence to the N-terminal segment of the proteolytically cleaved thrombin receptor, enhanced ANP release from adult rat cultured atrial myocytes. Our data suggest that thrombin may regulate ANP release from the cardiac atrium. This action involves activation of thrombin receptors in atrial myocytes.

Erythropoietin stimulates atrial natriuretic peptide secretion from adult rat cardiac atrium.

Hypoxia is a powerful stimulus for erythropoietin (EPO) secretion from the kidney and for atrial natriuretic peptide (ANP) secretion from atrial myocytes. EPO is involved in the long term defense mechanism against hypoxia via stimulation of erythropoiesis. ANP is involved in the short-term defense mechanism against hypoxia via improved pulmonary and heart functions. We investigated a possible interaction between these two hormones. We tested the hypothesis that EPO may stimulate ANP secretion from the cardiac atrium. This hypothesis was tested in two in vitro models; isolated rate atrium and cultured adult atria rat myocytes. Recombinant human EPO (5-10 units/ml) enhanced ANP secretion from the isolated atrium (by approximately 2-fold) within 10 min in a concentration-dependent manner. To define whether the action of EPO on ANP secretion is direct, we examined the effect of EPO on ANP release from adult rat cultured atrial myocytes. EPO failed to stimulate ANP secretion from cultured atrial myocytes, suggesting that EPO-induced ANP secretion is an indirect effect. Cyclooxygenase products (e.g.,prostaglandins) and endothelin 1 were shown to be potent secretagogues of ANP from cardiac atrium. To test whether EPO-induced ANP secretion from isolated perfused atrium is mediated by cyclooxygenase products and/or endothelin, we used inhibitors of the enzyme cyclooxygenase (indomethacin or aspirin) and the endothelin receptor ETA subtype antagonist BQ123. EPO-stimulated ANP secretion was not affected by indomethacin (10(-4) M) or aspirin (10(-4) M), whereas BQ123 (10(-6) M) completely abolished EPO-stimulated ANP secretion from cardiac atrium. Our results expand our knowledge on the interaction between EPO and ANP hormonal systems and the possible role in the acute defense mechanism against hypoxia.

Effects of ANP receptor antagonists on ANP secretion from adult rat cultured atrial myocytes.

Atrial natriuretic peptide (ANP) is a hormone-secreted predominantly by atrial myocytes. ANP exerts many of its actions via activation of the particulate guanylyl cyclase receptor ANPR-A and the formation of guanosine 3',5'-cyclic monophosphate (cGMP), which serves as a second messenger in the target cells. Using membrane-permeable cGMP analogues (8-bromo-cGMP and dibutyryl- cGMP), we first tested the hypothesis that ANP secretion by adult rat cultured atrial myocytes can be modulated through the second messenger cGMP. Second, we examined the effects of two competitive ANPR-A receptor antagonists, namely HS-142-1 and anantin, on cGMP formation and ANP secretion from cultured atrial myocytes. Cultured atrial myocytes secreted large quantities of immunoreactive (ir) ANP under basal conditions. We found that cGMP analogues inhibited basal irANP secretion from cultured atrial myocytes, whereas HS-142-1 and anantin had stimulating effects. HS-142-1 and anantin reduced cGMP formation in cultured atrial myocytes at basal conditions. These results suggest an autoregulatory mechanism of ANP secretion by atrial myocytes in an autocrine/paracrine fashion.