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C W Davis

Publications and source records attributed to C W Davis.

At least 55 records · Page 3Linked to original sources
PubMed1985

Effects of mucosal sodium removal on cell volume in Necturus gallbladder epithelium.

Necturus gallbladder epithelium transports sodium and chloride by a process that first involves the cellular entry of each ion across the apical membrane in an electrically silent process. In this paper we present results from cell volume and fluid flux measurements in the presence of different inhibitors and at normal and reduced sodium concentrations, which bear on the process by which ionic entry is effected. We find that reduction of mucosal sodium to a concentration of 10 mM has no effect on either cell volume or on the rate of transepithelial fluid transport, whereas the complete removal of sodium causes a significant decrease in cell volume in addition to its known inhibitory effect on fluid transport. Amiloride had no effect on cell volume at normal sodium concentrations but markedly reduced it when the sodium concentration was reduced to 10 mM. Amiloride, bumetanide, and dipyridamole markedly and reversibly inhibited fluid transport. Finally, the addition of ouabain to the serosal medium induced cell swelling, which was prevented by the removal of potassium from the mucosal medium. These results indicate that the process of sodium entry at the apical membrane is complicated and likely includes both cotransport (NaCl or Na-K-2Cl) and parallel exchange (Na-H and Cl-HCO3) transport mechanisms, and that the proportion of NaCl transported by the different mechanisms varies with the conditions.

Amiloride↗
PubMed1985

Cell volume regulation in frog urinary bladder.

We have studied the problem of cell volume homeostasis in toad and frog urinary bladder by using electrophysiological measurements and an optical measure of cell volume. After osmotically induced swelling, urinary bladder cells spontaneously regulate their volume through a net loss of potassium, chloride, and water. During inhibition of sodium transport by amiloride the cells swell to the same extent as controls, but the volume-regulatory process is blocked. Electrophysiological results under isosmotic conditions indicate that basolateral membrane resistance increases simultaneously with the amiloride-induced rise in apical membrane resistance during transport inhibition. These independent observations indicate that inhibition of apical membrane sodium entry results in a secondary decrease in basolateral membrane potassium permeability. When cells are exposed to calcium-free, hyposmotic Ringer's solution, cell volume regulation is blocked; subsequent addition of the calcium ionophore A23187 is ineffective in restoring the regulatory process. The ionophore does induce volume regulation, however, in amiloride-inhibited, osmotically swollen cells in the presence of external calcium. Calcium thus seems to control basolateral membrane potassium permeability and may be the intracellular mediator of apical and basolateral membrane interactions.

Amiloride↗
PubMed1984

1-(4-Aminophenyl)isoquinoline derivatives. Potent inhibitors of calcium-independent and calcium-dependent phosphodiesterases from rat cerebral cortex.

The effects of a series of 1-(4-aminophenyl)isoquinoline derivatives on the activity of calcium-independent and calcium-dependent phosphodiesterases purified from rat cerebral cortex were examined. Agents were approximately equipotent (IC50 values, 0.2 to 25 microM) in inhibiting the calcium-dependent hydrolysis of either cyclic AMP or cyclic GMP, while they were 6-35 times more effective as inhibitors of cyclic AMP hydrolysis when compared to cyclic GMP hydrolysis using the calcium-independent enzyme. The diastereomers of 3-(carbomethoxy)propenamido demonstrated a marked difference in specificity. The cis-isomer was very potent in inhibiting cyclic AMP or cyclic GMP hydrolysis by either enzyme (IC50 values, 0.2 to 8 microM) while the trans-isomer was only effective in inhibiting calcium-independent cyclic AMP hydrolysis (IC50 values, 2.5 microM). Kinetic analyses of the type of inhibition of the calcium-dependent enzyme revealed that the various agents were competitive inhibitors of cyclic GMP hydrolysis and noncompetitive inhibitors of cyclic AMP hydrolysis. A reverse pattern of inhibition by the isoquinoline derivatives was found using the calcium-independent phosphodiesterase, i.e. noncompetitive inhibition of cyclic GMP while competitive inhibition of cyclic AMP. Inhibition of phosphodiesterases by these agents was also manifest using intact brain slices prepared from rat cerebral cortex. Thus, the agents were found to potentiate forskolin-elicited accumulations of cyclic AMP by 100-700% and increased the half-time for the decline in cyclic AMP following forskolin stimulation from 3 to 6 min.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1984

Assessment of selective inhibition of rat cerebral cortical calcium-independent and calcium-dependent phosphodiesterases in crude extracts using deoxycyclic AMP and potassium ions.

The effects of various inhibitors on the activity of calcium-independent and calcium-dependent phosphodiesterases from rat cerebral cortex were examined. While the agents varied greatly in their relative potency, each was found to be approximately equipotent in inhibiting the calcium-dependent hydrolysis of either cyclic AMP or cyclic GMP. In contrast, the inhibitors displayed a marked substrate specificity for the calcium-independent enzyme with ratios of IC50 values for inhibition of cyclic GMP hydrolysis when compared to cyclic AMP hydrolysis in decreasing order being: ZK 62711 (much greater than 100) greater than Ro 20-1724 (much greater than 25) papaverine (13) greater than 7-benzyl IBMX (4) greater than quercetin and kaempferol (2). The differential selectivity of the inhibitors for the two enzymes was most pronounced for ZK 62711 and Ro 20-1724 which were at least 25-100-times more potent in inhibiting the calcium-independent hydrolysis of cyclic AMP when compared to the calcium-dependent hydrolysis of cyclic AMP. In contrast, 7-benzyl IBMX, kaempferol and quercetin were 8-100-times more effective as inhibitors of cyclic GMP hydrolysis by the calcium-dependent phosphodiesterase while 7-benzyl IBMX and trimazosin displayed a similar enzyme selectivity using cyclic AMP as substrate. With the exception of papaverine, all agents were competitive inhibitors of the calcium-dependent phosphodiesterase. The type of inhibition observed with the calcium-independent enzyme was dependent on the substrate employed. The specificity of potassium ions in inhibiting the activity of the calcium-dependent phosphodiesterase and deoxycyclic AMP in inhibiting the calcium-independent enzyme was found to provide a convenient means to assess the effects of agents on these activities in crude extracts of cerebral cortex.

Animals↗
PubMed1983

1-(4-Aminobenzyl)-and 1-(4-aminophenyl)isoquinoline derivatives: synthesis and evaluation as potential irreversible cyclic nucleotide phosphodiesterase inhibitors.

In an effort to increase the specificity of the potent phosphodiesterase inhibitor papaverine, we synthesized two series of novel 1-(4-aminobenzyl)- and 1-(4-aminophenyl)isoquinoline derivatives, incorporating alkylating moieties on the amine substituents. These compounds were evaluated for their inhibitory action on phosphodiesterase preparations from bovine heart and rat cerebral cortex. Studies were also conducted to determine whether these compounds were reacting with the enzymes in an irreversible manner. The compounds were potent inhibitors of the phosphodiesterases; however, no evidence was found for an irreversible inhibition.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1982

Selective alteration of Ca2+-dependent and Ca2+-independent cyclic nucleotide phosphodiesterase activity in rat cerebral cortex by cyclic nucleotides and their analogs.

The effects of various cyclic nucleotides and cyclic nucleotide analogs on the activity of Ca2+-independent and Ca2+-dependent phosphodiesterases purified from rat cerebral cortex were examined. The order of potency for inhibition of the Ca2+-dependent enzyme by the various agents was the same using either cAMP or cGMP as substrate with 2'-O-monobutyryl cGMP, cIMP and 2-deoxy cGMP being the most potent. The inhibition of deoxy cGMP using cAMP or cGMP as substrate was competitive, with Ki values of 11 and 13 microM, respectively. In marked contrast, hydrolysis of cAMP or cGMp by the Ca2+-independent enzyme was stimulated 50-75% by cIMP, deoxy cGMP and N2-monobutyryl cGMP with EC50 values of 7, 20 and 30 microM, respectively. cGMP (EC50, 1.5 microM) produced quantitatively the same degree of stimulation of cAMP hydrolysis by the Ca2+-independent phosphodiesterase and the activation was not additive with that of deoxy cGMP. Of the other derivatives examined, 2'-O-monobutyryl cAMP and 2'-deoxy cAMP were the most potent inhibitors of cAMP hydrolysis by the Ca2+-independent enzyme and were 30-60 times more effective in inhibiting cAMP hydrolysis as compared to cGMP hydrolysis. The specificity of K+ in inhibiting the activity of the Ca2+-dependent phosphodiesterase and deoxy cAMP in inhibiting the Ca2+-independent enzyme may provide convenient means to examine specifically these activities in crude extracts from rat cerebral cortex.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1982

Sodium transport effects on the basolateral membrane in toad urinary bladder.

In toad urinary bladder epithelium, inhibition of Na transport with amiloride causes a decrease in the apical (Vmc) and basolateral (Vcs) membrane potentials. In addition to increasing apical membrane resistance (Ra), amiloride also causes an increase in basolateral membrane resistance (Rb), with a time course such that Ra/Rb does not change for 1-2 min. At longer times after amiloride (3-4 min), Ra/Rb rises from its control values to its amiloride steady state values through a secondary decrease in Rb. Analysis of an equivalent electrical circuit of the epithelium shows that the depolarization of Vcs is due to a decrease in basolateral electromotive force (Vb). To see of the changes in Vcs and Rb are correlated with a decrease in Na transport, external current (Ie) was used to clamp Vmc to zero, and the effects of amiloride on the portion of Ie that takes the transcellular pathway were determined. In these studies, Vcs also depolarized, which suggests that the decrease in Vb was due to a decrease in the current output of a rheogenic Na pump. Thus, the basolateral membrane does not behave like an ohmic resistor. In contrast, when transport is inhibited during basolateral membrane voltage clamping, the apical membrane voltage changes are those predicted for a simple, passive (i.e., ohmic) element.

Amiloride↗
PubMed1982

Neuroendocrine control of Na+ balance in the fiddler crab Uca pugilator.

The hemolymph ionic composition and unidirectional Na+ fluxes were analyzed in fiddler crabs (Uca) acclimated to 500 mosmol seawater. Eyestalkless crabs had lower hemolymph osmotic, Na+, and Cl- concentrations. The Na+ efflux was increased from 13.6 +/- 0.6 in control crabs to 19.6 +/- 1.3 mueq.g-1.h-1 in eyestalkless crabs; this increase was shown to be due to a higher Na+ permeability in eyestalkless crabs. Hemolymph Na+ in eyestalkless crabs was increased by an injection of eyestalk extract. The Na+ influx was increased from 11.1 in intact to 15.8 mueq.g-1.h-1 in eyestalkless animals. A kinetic study showed that 1) the influx was higher at all external Na+ concentrations in eyestalkless and intact-Na+-depleted crabs than in intact controls, and 2) the influx mechanism exhibited allosterism. The elevated Na+ influx in eyestalkless crabs was decreased by an injected eyestalk extract. An injected brain extract caused in increase in the Na+ influx in intact animals. It is concluded that the Na+ uptake mechanism is activated by decreasing the hemolymph Na+ concentration and that a brain hormone mediates the effect.

Animals↗
PubMed1979

A simple direct assay of 3',5'-cyclic nucleotide phosphodiesterase activity based on the use of polyacrylamide-bononate affinity gel chromatography.

A rapid, simple, and direct assay for 3',5'-cyclic nucleotide phospho-diesterase activity is based on the effective separation of cyclic AMP, cyclic GMP or cyclic CMP from their corresponding 5'-nucleotides and nucleosides by chromatography on a polyacrylamide-boronate gel. The affinity of the boronate residue for cis-diols results in the retention of 5'nucleotides and nucleosides while 3',5'-cyclic nucleotides are not retained. The coelution of all 5'-nucleotides and nucleosides allows for the accurate assessment of phosphodiesterase activity in preparations contaminated by other purine metabolizing enzymes such as 5'-nucleotidases and nucleotide and nucleoside deaminases. Phosphodiesterase activity assayed by this means yields linear reaction kinetics with respect to time and amount of enzyme protein. Low blank values obtained allow for detection of as little as 2-3% conversion of substrate to product.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1978

Calcium-dependent 3':5'-cyclic nucleotide phosphodiesterase. Inhibition of basal activity at physiological levels of potassium ions.

A calcium-dependent cyclic nucleotide phosphodiesterase from rat cerebrum was, in the absence of activator protein, inhibited by various monovalent cations. The inhibition was rapid, readily reversible, and concentration-dependent, with 100 mM cesium, rubidium, or potassium ion inhibiting essentially all basal enzyme activity, while 100 mM sodium or lithium ions produced only moderate inhibition. The potency of the cations in inhibiting the enzyme was Cs greater than or equal to Rb greater than K greater than Na greater than or equal to Li. Potassium ions increased the apparent Km for cyclic GMP and cyclic AMP by 3- and 5-fold, respectively. At 100 mM, the monovalent cations inhibited enzyme activated by the calcium-dependent activator by only 15 to 30%, while at 55 mM no inhibition pertained. Potassium and sodium ions at 55 mM had no effect on the calcium-independent phosphodiesterase from rat cerebrum. The results indicate that at normal intracellular concentrations of potassium ions the activity of the calcium-dependent phosphodiesterase is virtually completely dependent on the presence of calcium plus activator protein.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1977

Modified cyclic nucleotide systems in Morris hepatoma 3924A favoring expression of cyclic GMP effect.

Modifications in the cyclic nucleotide systems favoring the expression of cyclic GMP effects were found to occur in the transplanted fast-growing Morris hepatoma 3924A. These included: (a) a decreased level of cyclic GMP phosphodiesterase and an increased level of cyclic AMP phosphodiesterase; (b) a disproportionately increased level of cylic GMP-dependent protein kinase relative to that of cyclic AMP-dependent protein kinase; (c) a disproportionately increased level of stimulatory modulator of cyclic AMP-dependent protein kinase relative to that of inhibitory modulator of cyclic AMP-dependent protein kinase; and (d) an increased level of phosphoprotein phosphatase.

3',5'-Cyclic-AMP Phosphodiesterases↗