Exponential Release Research Articles

9. Queues, storage and inventories : Some storage models in continuous time with random inputs and random outputs together with exponential release

9. Queues, storage and inventories : Some storage models in continuous time with random inputs and random outputs together with exponential release

Heavy meromyosin Mg-ATPase: presteady-state and steady-state Hplus release.

The presteady state and steady state release of protons during hydrolysis of ATP by myosin has been studied by using a proteolytic subfragment of myosin, heavy meromyosin, isolated from rabbit skeletal muscle. Under the conditions of 0.5 M KCl, 9 mM MgCl(2), pH 8, and 25 degrees , the rate of the H(+) initial burst is proportional to the concentration of ATP added, and shows no plateau even when the concentration of ATP added is increased up to 750 muM. The apparent second order rate constant is approximately 7 x 10(5) M(-1) sec(-1). When the concentration of ATP added is equal to or less than the concentration of heavy meromyosin catalytic sites, the H(+) initial burst is followed by a slow exponential release of H(+) with a rate constant of 0.017 sec(-1). This rate constant is equal to the steady state rate constant calculated for each heavy meromyosin catalytic site, suggesting that both sites split ATP independently. The magnitude of the H(+) released per ATP bound is always 0.4 in the initial burst, and 0.6 in the slow exponential phase, which equals to a total of 1 H(+) released per ATP hydrolyzed. On the basis of these observations, it is concluded that the H(+) initial burst may well represent a fast ionization of H(+) due to a conformational change as a result of nucleotide binding.

A finite dam with exponential release

This paper considers a finite dam with independently and identically distributed (i.i.d.) inputs occurring in a Poisson process; the special cases where the inputs are (i) deterministic and (ii) negative exponentially distributed are considered in detail. The instantaneous release trate is proportional to the content, i.e., there is an exponential fall in conten except when inputs occur. This model may arise in several other situations such as a geiger counter or integrated shot noise. The distribution of the number of inputs, and of the time, to first overflowing is obtained in terms of generating functions; in Case (i) the solution is obtained through recurrence relations involving iterated integrals which can be evaluated numerically, and in Case (ii) using a series solution of a second order differential equation. Numerical results, in particular for the first two moments, are obtained for various values of the parameters of the model, and compared with a large number of simulations. Some remarks are also made about the infinite dam.

A finite dam with exponential release

This paper considers a finite dam with independently and identically distributed (i.i.d.) inputs occurring in a Poisson process; the special cases where the inputs are (i) deterministic and (ii) negative exponentially distributed are considered in detail. The instantaneous release trate is proportional to the content, i.e., there is an exponential fall in conten except when inputs occur. This model may arise in several other situations such as a geiger counter or integrated shot noise. The distribution of the number of inputs, and of the time, to first overflowing is obtained in terms of generating functions; in Case (i) the solution is obtained through recurrence relations involving iterated integrals which can be evaluated numerically, and in Case (ii) using a series solution of a second order differential equation. Numerical results, in particular for the first two moments, are obtained for various values of the parameters of the model, and compared with a large number of simulations. Some remarks are also made about the infinite dam.

Purified ovine growth hormone releasing factor: effects on growth hormone secretion and pituitary cyclic nucleotide accumulation.

Growth hormone releasing factor (GRF) was purified from ovine hypothalami on a Sephadex G-25 column. Three fractions from one of the major protein peaks induced the release of radioimmunoassayable growth hormone (GH) from rat pituitaries incubated <i>in vitro</i>, but did not induce any appreciable release of other anterior pituitary hormones. The kinetics of GH release from rat pituitaries included an initial phase with an exponential release of hormones, a subsequent phase with a constant rate of release, and a terminal declining rate of release seen with high GRF doses. The minimally effective dose of this GRF preparation which stimulated GH secretion <i>in vitro</i> contained 1.5 <i>µ</i>g of protein. No change in pituitary cyclic AMP was observed following the exposure of the explants to 3 or 6 <i>µg </i>of GRF for 10 min, but proportional increases in pituitary cyclic GMP were observed at this time period. Although the synthetic decapeptide, Val-His-Leu-Ser-Ala-Glu-Glu-Lys-Glu-Ala, has been shown to deplete bioassayable pituitary GH, it did not stimulate the release of radioimmunoassayable GH nor did it substantially elevate the pituitary cyclic AMP content at the dose levels and time intervals tested. The synthetic decapeptide did not alter pituitary cyclic GMP content after 10 or 60 min of incubation. These observations further substantiate that GRF capable of releasing radioimmunoassayable GH can be isolated from hypothalamic tissue. Preliminary studies of the mechanism of action of GRF indicate that cyclic GMP rather than cyclic AMP plays a central role in mediating the neurohormonal control of GH release.

Osmotic factors determining the release of catecholamines from isolated chromaffin cell granules.

AbstractLishajko, F. Osmotic factors determining the releme of catecholamines from isolated chromaffin cell granules. Acta physiol. scand. 1970. 79. 64–75.On incubation of bovine adrenal medullary granules in isotonic sucrose, KCl, NaCl or K‐phosphate, noradrenaline (NA) is initially released at a rapid rate followed by a slow exponential release. Adrenaline (A) release in the same media does not show the rapid initial phase. In hypotonic media both NA and A show a rapid initial release while in hyper‐tonic solutions both NA and A are released at a constant slow rate (t/2 = 115–185 min at 37°). Partial replacement of sucrose or dextrose media by NaCI, KCl or K‐phosphate decreases the release rate of Na and A. Addition of 6 mM Mg2+ or Ca2+ prevents the initial rapid fall of NA and of A in hypotonic solution. ATP‐Mg2+ inhibits the release rate of catecholamines in chloride free media more than ATP or Mg2+ alone. The granules were shown to shrink in the presence of divalent ions, as well as on addition of ATP or ATP‐Mg2+. During partial lysis or “osmotic shock” the granules lose slightly more A than NA. The results suggest that the NA containing granules from chromaffin cells initially possess a higher osmotic pressure than that of the A granules, possibly depending on the rate of splitting of an amine‐ATP‐complex. The release may depend partly on the ensuing osmotic equilibration process.

Paths of phosphate transfer in normal chick embryo cells and in cells infected with vesicular stomatitis virus.

SUMMARY: The paths of phosphate transfer were compared in normal and vesicular stomatitis virus-infected chick embryo cell monolayers during one-step virus growth. Phosphate entered the normal cell via an inorganic pool in reversible equilibrium with external phosphate, and passed to large-molecule phosphate from this pool or from organic acid-soluble phosphate. During the latent and exponential release periods of virus infection there was no detectable slowing or stimulation of the rate of gain of 32P by acid-soluble inorganic and organic phosphates (AI and AO), lipid phosphate (LP), ribonucleic acid (RNA) and other phosphate fractions until uptake ceased in nearly all fractions about half-way through exponential release. Negligible P or 32P entered or left deoxyribonucleic acid (DNA) in normal or infected cells in this system. Before and during exponential release there was no detectable lysis of nuclei, mitochondria or microsomes (examined after isolation), and no detectable loss of 32P from AI, AO, LP, RNA or DNA, except for a late 30-50 % decrease in the 32P of the sucrose-soluble RNA of disrupted cells. This could be a secondary effect (i.e. onset of cell death) rather than an essential stage of virus growth. Gross lysis was evident in all fractions 20 hr. after infection, with the exception of the acid-soluble inorganic fraction not in reversible equilibrium with the medium.