Distinct Physiological States Research Articles

Microelectrode studies on Malpighian tubule cells of Locusta migratoria: Effects of external ions and inhibitors

Basal and apical membrane potentials were recorded from Malpighian tubules of Locusta using intracellular microelectrodes. Ion substitution experiments, involving Na +, K + and Cl − in the bathing media, indicated that the basal membrane was more permeable to K + than Na + or Cl −. Two different electrical responses to high [K +] salines were noted and these probably reflect distinct physiological states of basal membrane permeability. Experiments with ouabain and orthovanadate suggested that whilst (Na + + K +)-ATPase activity was not significantly electrogenic, asymmetric ionic distribution across the basal membrane was partly maintained by this enzyme. The actions of furosemide and bumetanide indicated that chloride might cross the basal membrane by a cation co-transport mechanism. In addition, data from ion substitution experiments suggest that Cl − entry across the basal membrane is K +-dependent. The responses to Na +-free and Cl −-free salines bring into question the role of Na + in the entry of chloride across the basal membrane by co-transport.

Influence of cerebroventricular injection of dopamine on plasma prolactin and LH levels of postlaying and broody turkey hens

Dopamine (DA), a well-known inhibitor of prolactin secretion in mammals, was injected into the third cerebroventricle of turkey hens in two distinct physiological states. Non-broody postlaying turkeys had preinjection plasma prolactin (Prl) levels of about 68 ng/ml. Prolactin levels were significantly elevated 20 and 40 min after intraventricular injection of 10 μg of dopamine and then returned to basal levels. Incubating turkey hens, in contrast, showed the typical hyperprolactinemia characteristic of this physiological state. Mean preinjection Prl levels ranged from about 1290 to 1860 ng/ml. Injection of 10 or 30 μg of dopamine neither increased nor decreased plasma Prl levels over the 120-min time course of this experiment. Plasma luteinizing hormone (LH) levels were increased in nonbroody postlaying hens within 40 min after intraventricular injection of 10 μg of DA and then declined. Levels in vehicle-injected hens did not change significantly up to 120 min after injection. Dopamine injection had no effect on LH levels of broody turkey hens. These data clearly show that DA is not an inhibitor of Prl secretion in nonlaying turkeys with moderate Prl levels and in fact it appears to stimulate its release.

Imaging X-ray spectrometer : Patrick A Grant, John W Jackson, George Alcorn, Francis Marshall assigned to The United States of America as represented by the Administrator of the National Aeronautics and Space Administration

Protein switches are ubiquitous in biological signal transduction systems, enabling cells to sense and respond to a variety of molecular queues in a rapid, specific, and integrated fashion. Analogously, tailor-engineered protein switches with custom input and output functions have become invaluable research tools for reporting on distinct physiological states and actuating molecular functions in real time and in situ. Here, we analyze recent progress in constructing protein-based switches while assessing their potential in the assembly of defined signaling motifs. We anticipate such systems will ultimately pave the way towards a new generation of molecular diagnostics and facilitate the construction of artificial signaling systems that operate in parallel to the signaling machinery of a host cell for applications in synthetic biology.

Recent 31 P n.m.r. studies of myocardium

Earlier work from this laboratory has concerned the possible use of phosphorus n.m.r. as a method to monitor, in a non-invasive manner, the biochemical state of the perfused heart as a function of its mechanical performance. We showed that a simulated coronary infarction could be detected by 31 P n.m.r. (Hollis et al 1978 a and that hypothermia and KC1 arrest could preserve the pH and the ATP levels at more nearly normal values than in a non-arrested heart during long periods (40 min) of ischaemia (Hollis et al . 1978 b ).More recently it was shown that multiple doses of KC1, given at intervals, were more effective in this respect than was a single dose (Flaherty et al . 1979). These studies essentially followed the kinetics of transitions of the heart between two or more distinct physiological states (i.e. normoxic and ischaemic, with or without KC1 arrest) by observation of the 31 P n.m.r. spectra at various time intervals over periods of up to 1 h. As described in detail and demonstrated in Dr Truman Brown’s contribution to these discussions, the rates of chemical exchange reactions occurring in a steady state can be measured by the techniques of saturation transfer in various biological systems, including perfused hearts.