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D L Gill

Publications and source records attributed to D L Gill.

72 records · Page 4Linked to original sources
PubMed1982

Sodium channel, sodium pump, and sodium-calcium exchange activities in synaptosomal plasma membrane vesicles.

Two mechanisms of Na+ influx have been observed using synaptosomal plasma membrane vesicles purified by density gradient centrifugation from a synaptosomal hypotonic lysate. First, a 5-fold increase in uptake over basal Na+ entry occurs with 50 microM veratridine. The veratridine-dependent Na+ uptake is partially inhibited by 2 microM tetrodotoxin with an apparent time dependency of action (half-maximal inhibition in approximately 20 min). Second, a larger Na+ accumulation (approximately 15-fold above basal) was observed with 2.5 mM ATP, this effect being dependent on internal K+ loading of vesicles although inhibited by high external K+. The two uptake processes are believed to represent operation of the plasma membrane voltage-sensitive Na+ channel, and the Na+-pumping (Na+ + K+)-ATPase, respectively. Both Na+ flux mechanisms appear to operate in a single population of vesicles since opening of the Na+ channel with veratridine diminishes the ATP-dependent accumulation of Na+ by over 75%. An inverted orientation of the plasma membrane vesicles is likely to account for the functioning of the ATP-dependent Na+ pump and may also account for the low sensitivity and time dependency of the inhibitory action of tetrodotoxin on Na+ channel-opening. Na+ accumulated by the Na+ pump was rapidly effluxed by 10 mM external Ca2+ via the Na+-Ca2+ exchange mechanism which (together with an ATP-dependent Ca2+-accumulating mechanism) was recently characterized in the vesicles (Gill, D. L., Grollman, E. F., and Kohn L. D. (1981) J. Biol. Chem. 256, 184-192). This result, together with the observed inhibition of Ca2+ influx via (Na+-Ca2+)-exchange due to veratridine-mediated Na+ flux, strongly suggests that the Na+ pump, Na+ channel, and both Ca2+ transport mechanisms function in a single population of inverted plasma membrane vesicles.

Animals↗
PubMed1982

Opiate receptor-mediated inhibition of adenylate cyclase in rat striatal plasma membranes.

Plasma membranes from rat striatum contain adenylate cyclase activity that is subject to dual regulation by GTP. Low concentrations (up to 30 nM) of the nucleotide increase activity whereas higher concentrations evoke a steady decline in activity; such behavior characterizes dually regulated adenylate cyclase systems. The opiates, morphine sulfate and D-Ala-Met-enkephalin, produce naloxone-reversible inhibition of the enzyme that is dependent on "inhibitory concentrations" of GTP (above 50 nM). In the absence of GTP no inhibition is observed. Sodium ions decrease the inhibition of activity promoted by GTP alone, but amplify the degree of inhibition seen in the presence of the opiates and GTP. The potencies of the opiates in mediating these effects mirror their affinities for delta opiate receptors in striatum. It is suggested that this action of the opiates may represent their primary action in striatum.

Adenylyl Cyclase Inhibitors↗
PubMed1981

Calcium transport mechanisms in membrane vesicles from guinea pig brain synaptosomes.

Ca2+ transport mechanisms were investigated using membrane vesicles prepared from guinea pig brain synaptosomes by hypotonic lysis. Two major mechanisms of Ca2+ transport exist, Na+-Ca2+ exchange and ATP-dependent Ca2+ uptake. A third although minor component of Ca2+ uptake occurs under hyperpolarizing conditions (determined by increased uptake of [3H]tetraphenylphosphonium+). Na+-Ca2+ exchange results in a rapid increase of [Ca2+]i (up to 100-fold above [Ca2+]O), has a Km for Ca2+ of 40 microM, is fully reversed by added external Na+, is inhibited by agents dissipating Na+ gradients (monensin or veratridine), and is uninfluenced by mitochondrial inhibitors. ATP-dependent Ca2+ uptake has a higher affinity for CA2+ (Km = 12 microM), is dependent on Mg2+ or Mn2+, and is inhibited by beta, gamma-imidoadenosine 5'-triphosphate and VO43-, although only slightly (20%) inhibited by high concentrations of mitochondrial inhibitors. Both mechanisms are temperature-dependent, fully reversed by A23187, and higher in the presence of external K+. Ca2+ loaded in vesicles via ATP-dependent Ca2+ uptake is rapidly effluxed upon addition of external Na+ (as for Na+-Ca2+ exchange). Therefore a single population of vesicles exists containing both Ca2+ transport mechanisms. The two mechanisms are independent since they accumulate Ca2+ additively, are selectively inhibited by monensin and VO43-, and show distinct specificity toward other divalent cations and La3+. Although independent, Na+ (100 mM) inhibits ATP-dependent Ca2+ uptake (Km for ATP increased from 40 to 300 microM) in the absence of any net Na+ movement. Since Na+-Ca2+ exchange functions in the synaptosomal plasma membrane, the results suggest that both Ca2+ transport mechanisms originate from this membrane and function in the present experiments in inverted plasma membrane vesicles.

Animals↗
PubMed1980

Effects of immunoglobulins upon the interaction of thyrotropin with receptor in human fat tissue.

TSH bound to human fat membranes is shown to be unusually sensitive to the addition of immunoglobulin G (IgG). Significant displacement was observed with 10 microgram/ml, and 50% displacement was obtained with 50-100 microgram/ml IgG prepared from control sera pooled from euthyroid subjects. It was not possible to demonstrate increased TSH displacement by IgG preparations from sera of thyrotoxic compared to that of euthyroid subjects using human fat membranes, as was demonstrable with human thyroid membranes. The increased sensitivity of fat membranes to IgG was not due to nonspecific protein interactions and is suggested to derive from interactions with Fc receptors associated with fat membranes.

Adipose Tissue↗
PubMed1979

The prediction of group motor performance from individual member abilities.

Two experiments were conducted to investigate the prediction of group performance on the motor-maze task from individual member abilities. In both experiments subjects performed 20 individual trials on the maze task in an initial session prior to the actual experiment. On the basis of these individual performance scores, two-person groups were formed so that the groups represented a range of average ability levels and a range of discrepancies in abilities between partners. In Experiment 1, all groups performed a cooperative and a noncooperative group task in separate sessions both involving competition with another group. Only the cooperative group task was used in Experiment 2, but all groups performed under both competitive and noncompetitive conditions. Multiple regression analyses yielded a moderate, positive relationship between member abilities and group performance in both experiments; group performance on the highly cooperative task was dominated by the lower-ability partner.

Journal Article↗
PubMed1978

Characterization of thyrotropin binding to specific receptors in human fat tissue.

Specific receptors for thyrotropin were found to exist in membranes from whole human subcutaneous fat tissue. The characteristics of the interaction of 125I-labelled thyrotropin with such receptors were determined and compared with the stable, high-affinity thyrotropin receptor shown previously to exist in guinea pig fat membranes. Specific binding was readily detectable using low concentrations of membranes (up to 80 microgram/ml), though specific binding was reduced at higher membrane concentrations. Increasing concentrations of unlabelled thyrotropin reduced fractional binding, revealing saturation of a population of mixed affinity sites (highest Ka of the order of 0.3 X 10(9) M-1). Little cross-reactivity was observed with other lipolytic or structurally related hormones, though some cross-reactivity was observed in the presence of human chorionic gonadotropin. Association was temperature-dependent and rapid at 37 degrees C, though prolonged incubation revealed some instability of binding at this temperature. Binding was reversible with a high dissociation rate constant, and was particularly sensitive to the presence of low concentrations of sodium or calcium ions. Using membranes prepared from isolated human fat cells, binding of thyrotropin was equally sensitive to the addition of cations.

Adipose Tissue↗
PubMed1976

Competitive trait anxiety, success-failure and sex as determinants of motor performance.

Two experiments determined the effects of competitive trait anxiety, success-failure, and sex on the performance of 10- to 12 yr.-old children competing on a complex motor maze. Competitive trait anxiety was assessed by the Sport Competition Anxiety Test and success-failure was induced by giving bogus win-loss feedback. High and low competitive trait-anxiety children were randomly assigned to one of three conditions: winning 80%, 50% or 20% of 20 contests. The average completion time and the variability of times within each of two blocks of 10 contests were the two performance measures. State-anxiety was assessed with Spielberger's State Anxiety Inventory for Children as an indicant of arousal prior to and during competition. The findings of Exp. 1 yielded no significant performance differences. In Exp. 2 a significant interaction of competitive trait anxiety X success-failure X sex for performance time and variability was obtained. This interaction was largely attributed to sex differences.

Achievement↗
PubMedDate not supplied

Ca2+ release from endoplasmic reticulum is mediated by a guanine nucleotide regulatory mechanism.

Ca2+ accumulation and release from intracellular organelles is important for Ca2+-signalling events within cells. In a variety of cell types, the active Ca2+-pumping properties of endoplasmic reticulum (ER) have been directly studied using chemically permeabilized cells. The same preparations have been extensively used to study Ca2+ release from ER, in particular, release mediated by the intracellular messenger inositol 1,4,5-trisphosphate (InsP3). So far, these studies and others using microsomal membrane fractions have revealed few mechanistic details of Ca2+ release from ER, although a recent report indicated that InsP3-mediated Ca2+ release from liver microsomes may be dependent on GTP. In contrast to the latter report, we describe here the direct activation of a specific and sensitive guanine nucleotide regulatory mechanism mediating a substantial release of Ca2+ from the ER of cells of the neuronal cell line N1E-115. These data indicate the operation of a major new Ca2+ gating mechanism in ER which is specifically activated by GTP, deactivated by GDP, and which appears to involve a GTP hydrolytic cycle.

Animals↗