Dynamics of DNA supercoils.

DNA in cells exhibits a supercoiled state in which the double helix is additionally twisted to form extended intertwined loops called plectonemes. Although supercoiling is vital to many cellular processes, its dynamics remain elusive. In this work, we directly visualize the dynamics of individual plectonemes. We observe that multiple plectonemes can be present and that their number depends on applied stretching force and ionic strength. Plectonemes moved along DNA by diffusion or, unexpectedly, by a fast hopping process that facilitated very rapid (<20 milliseconds) long-range plectoneme displacement by nucleating a new plectoneme at a distant position. These observations directly reveal the dynamics of plectonemes and identify a mode of movement that allows long-distance reorganization of the conformation of the genome on a millisecond time scale.

Effect of corticotropin releasing factor on atrial natriuretic peptide release from the isolated perfused rat heart.

The effect of corticotropin releasing factor (CRF) on atrial natriuretic peptide (ANP) release and its possible modulation by indomethacin, norepinephrine, propranolol and nitro-L-arginine (an inhibitor of the endothelium-derived relaxing factor (EDRF) release) was investigated, using an isolated perfused rat heart preparation. Bolus injection of 5 micrograms CRF, dissolved in 100 microliters perfusion buffer, provoked a significant (p < 0.01 vs. control) short-time increase of ANP release. Indomethacin (3 x 10(-5) mol/l) inhibited the CRF-stimulated increase of ANP release and decreased the basal ANP secretion (p < 0.01 vs. CRF group). Norepinephrine (10(-9) mol/l) slightly, but not significantly, decreased the CRF-stimulated ANP release and did not change the basal ANP output. Propranolol (3 x 10(-6) mol/l) did not alter ANP release. Nitro-L-arginine (3 x 10(-5) mol/l) increased the basal ANP release (p < 0.01 vs. CRF group) and prolonged the CRF-induced rise of the ANP secretion. The present data suggest that prostaglandins are important mediators of basal and CRF-stimulated ANP release and that EDRF might be a physiological inhibitor of ANP release.

Effects of corticotropin-releasing factor on isolated rat heart activity.

We investigated effects of bolus administration of corticotropin-releasing factor (CRF) on parameters of cardiac activity in isolated working rat hearts. Effects at a dose of 5 micrograms of CRF were compared in hearts perfused with Krebs-Henseleit solution, norepinephrine (NE, 10(-9) M), propranolol (3 x 10(-6) M), NG-nitro-L-arginine (L-NNA, 3 x 10(-5) M), or indomethacin (3 x 10(-5) M). CRF increased coronary flow for > 30 min (P < 0.01) with maximum increases of 31.7%, suggesting a prolonged vasodilatory action of the peptide. CRF, in addition, induced transient (lasting < 10 min) increases in maximum aortic pressure and oxygen consumption (P < 0.01), suggesting an inotropic action of the peptide. Perfusions of NE and propranolol did not change the cardiac response to CRF. L-NNA, inhibiting release of endothelium-derived relaxant factor (EDRF), and indomethacin diminished the vasodilatory response to CRF, as indicated by significantly shortened increases in coronary flow after CRF (P < 0.05). Indomethacin also enhanced peak increases in maximum aortic pressure after CRF (P < 0.01). The data confirm direct effects of CRF on cardiac activity. They also suggest that the mediation of coronary vasodilation by CRF involves the endothelial release of prostacyclin and EDRF.

Dilatory and inotropic effects of corticotropin-releasing factor (CRF) on the isolated heart. Effects on atrial natriuretic peptide (ANP) release.

The effects of CRF administration on cardiac performance, coronary flow and ANP release were investigated in the rat heart. Isolated hearts were perfused at a constant filling pressure according to working heart model with a Krebs-Henseleit solution containing glucose and insulin, saturated with a gas mixture containing 95% O2 and 5% CO2. Administration of CRF via a cannula into the left atrium elicited a prolonged increase in the coronary flow rate and a transient increase in the aortic pressure resulting in an overall increase in the pressure-volume work. The oxygen consumption, after the administration of CRF, increased in accordance with the cardiac effort. No changes were observed in the spontaneous heart rate. Furthermore, administration of CRF induced a short-term increase of ANP release into the coronary perfusate. Our experiments suggest that administration of CRF produces a prolonged dilatory effect on the coronary arteries while producing a transient positive inotropic effect and a transient increase of ANP release on the isolated rat heart.

Calcium antagonism and protection of tissues from calcium damage.

Calcium antagonism of nifedipine, nitrendipine or nisoldipine prevented salt-induced hypertension, renovascular damage and mortality in Dahl salt-sensitive (S) rats. The calcium agonist BAY K 8644 accelerated the development of salt-induced hypertension in S rats. In some S rats on a low-salt diet BAY K 8644 induced renovascular damage without sustained hypertension. In stroke-prone spontaneously hypertensive rats (SHRSP) on a normal diet the natural appearance of stroke was correlated with an increased calcium content in brain and kidney tissue. Nimodipine prevented stroke and the increase in brain calcium content without affecting the high blood pressure. A similar protective effect without substantial influence on high blood pressure was achieved by bilateral parathyroidectomy. Hypertension-associated vascular damage does not necessarily depend on the systemic intravascular pressure. In malignant hypertension the deleterious calcium overload in tissues may be activated or inhibited independently of the regulation of arterial blood pressure.