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F T Crews

Publications and source records attributed to F T Crews.

At least 19 recordsLinked to original sources
PubMed1992

Concentrations of carbachol stimulating phosphoinositide hydrolysis cause a sustained decrease in membrane potential and firing rate: role of inositol and inositol polyphosphate second messengers.

We have investigated the relationship between muscarinic agonist-stimulated phosphoinositide (PI) hydrolysis and electrophysiological responses in rat hippocampal slice preparations. In a previous extracellular study, we found that muscarinic agonists at concentrations that stimulate PI hydrolysis result in a biphasic firing response; an initial increase in firing followed by loss of firing at higher concentrations. To test the hypothesis that variability in obtaining consistent loss of firing is related to depletion of intracellular inositol, we investigated the effects of adding exogenous inositol to the buffer. We now report that concentrations of inositol similar to those in cerebral spinal fluid (30-100 microM) augment carbamylcholine (carbachol, CCh) mediated loss of firing and [3H]inositol-1,3,4,5-tetrakisphosphate ([3H]Ins(1,3,4,5)P4) formation. Inhibition of firing produced by 30 microM CCh in the presence of inositol was associated with a sustained depolarization of 20-25 mV, an increased slope resistance in the depolarized range (-60 to -40 mV), and a parallel shift in the hyperpolarized (-100 to -70 mV) range of the voltage-current curve and increased frequency of spontaneous IPSPs. Under voltage-clamp, measurements of the M-current (IM) showed sustained inactivation by CCh with reversal after washout of CCh. Manual depolarization of cells by current injection to the same level of depolarization as attained with CCh did not usually lead to the same loss of firing. These findings suggest that IM, and possibly other voltage-independent currents or ion pumps, may cause loss of firing only in part through a depolarization blockade of firing and not through desensitization. Furthermore, CCh treatment without inositol did not depolarize neurons as much as CCh with inositol, and usually did not cause a delayed loss of firing. Brain slice preparations may thus require physiological concentrations of inositol to show consistent or maximum phosphoinositide-mediated electrophysiological responses.

Action Potentials↗
PubMed1992

Angiotensin II receptor subtypes play opposite roles in regulating phosphatidylinositol hydrolysis in rat skin slices.

Among the many functions of angiotensin II (Ang II) it now appears that Ang II is a growth factor. The concentration of Ang II in rat skin has been shown to increase during wound healing. To investigate the intracellular effect of Ang II in skin we determined the levels of total cytoplasmic inositol phosphates after incubation of skin slices with different doses of Ang II. 10(-6) M of Ang II increased significantly the phosphatidylinositol (PI) hydrolysis, and the effect was dose dependent up to 10(-4) M Ang II. The majority of inositol phosphates yielded after 1 hour incubation in the presence of lithium was InsP1, with lesser amount of InsP2. Losartan, the Ang II AT1 antagonist, at a dose of 10(-4) M blocked the effect of Ang II, while PD123319, the Ang II AT2 antagonist, had no antagonistic action; PD123319 at the higher dose of 10(-3) M, however, potentiated the effect of Ang II on PI hydrolysis. The results suggest that PI hydrolysis is a second messenger system for Ang II in rat skin. Also, the two subtypes of Ang II receptors mediate opposite effects on PI hydrolysis: Ang II binding to AT1 receptors increases inositol phosphate production, while Ang II binding to AT2 receptors decreases inositol phosphate production.

Angiotensin II↗
PubMed1992

Regulation of inositol transport by glucose and protein kinase C in mesangial cells.

Since inositol (Ins) depletion appears to be an important mechanism of cell injury in diabetic glomerulopathy, we studied Ins transport in cultured rat mesangial cells during hyperglycemia. High glucose stimulated [3H]-Ins uptake by 50 to 90% within 24 hours in a dose dependent manner. This effect was characterized by an increase in the Vmax of a Na(+)-dependent Ins transporter (10.3 +/- 0.2 vs. 16.4 +/- 0.4 pmol/mg/min, P less than 0.005). Since high glucose also induced activation of protein kinase C (PKC) in permeabilized mesangial cells, we examined the potential role of this enzyme in the stimulation of Ins transport by glucose. Both PKC inhibition with H7 and staurosporine, and down regulation of PKC by prolonged PMA (1.6 microM) treatment inhibited the stimulatory effect of glucose on Ins transport. In conclusion, high glucose stimulates Na(+)-dependent Ins transport in mesangial cells by a mechanism mediated by PKC. This process may represent an important adaptive response of mesangial cells to hyperglycemia.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1992

Insulin-like growth factor I receptor binding in brains of Alzheimer's and alcoholic patients.

Patients with chronic alcoholism and/or Alzheimer's disease show degenerative changes in the cerebral cortex and hippocampus. To investigate possible changes in insulin-like growth factor I receptor binding sites in brain tissue of patients with these pathological conditions, the number of 125I-insulin-like growth factor I binding sites was determined in tissues obtained from control patients and those with Alzheimer's and/or with a history of alcoholism. The four experimental groups examined consisted of patients from similar age groups. Postmortem histology and a clinical history were used for the diagnosis of Alzheimer's disease and alcoholism, respectively. Careful clinical records were kept concerning other variables such as immediate cause of death and medications administered before death. Specific binding of 125I-insulin-like growth factor I to homogenates prepared from cerebral cortex of Alzheimer's, alcoholic, alcoholic Alzheimer's, and age-matched control patients was similar, although Alzheimer's patients tended to have slightly higher binding values. No significant differences in insulin-like growth factor I binding in cerebral cortex were found with regard to age of patients, the interval between death and autopsy, and CNS-active medications. No statistical differences in 125I-insulin-like growth factor I binding were noted in hippocampal tissue from the four patient groups. Thus, human insulin-like growth factor I binding sites in cerebral cortex and hippocampus appear unaffected by several variables.

Alcoholism↗
PubMed1991

Binding of [125I]-insulin-like growth factor-1 (IGF-1) in brains of Alzheimer's and alcoholic patients.

Patients with chronic alcoholism and/or Alzheimer's disease suffer from degenerative changes in the cerebral cortex and hippocampus. To investigate possible changes in IGF-1 receptor binding sites in brain tissue of patients with these pathological conditions, the binding of [125I]-IGF-1 was determined in tissues obtained from control, Alzheimer's and/or patients with a history of alcoholism. The four experimental groups examined consisted of patients from similar age groups. Specific binding of [125I]-IGF-1 to cerebral cortical membranes from Alzheimer's patients had significantly more binding sites than age-matched controls, alcoholic patients and alcoholic patients with Alzheimer's disease. Regression analyses indicated that there were no significant differences in [125I]-IGF-1 binding in cerebral cortex with regard to age of patients (1.1% of total variance with a range of 52 to 92 years). Likewise, the time interval between death and autopsy contributed only 1.4% to the total variance in IGF-1 binding. No statistical differences in [125I]-IGF-1 binding were noted in hippocampal tissue from the various patient groups. Thus, human IGF-1 binding sites in cerebral cortex and hippocampus appear to be relatively stable for a number of variables. The increase in cerebral cortical [125I]-IGF-1 binding sites could be due to upregulation of IGF-1 receptors resulting from a decrease in IGF-1 levels in Alzheimer's patients.

Alcoholism↗
PubMed1991

Differences in imidazoline and phenylethylamine alpha-adrenergic agonists: comparison of binding affinity and phosphoinositide response.

The imidazoline class of compounds, reported to be partial agonists at alpha 1 adrenoceptors, were compared with phenylethylamines for their ability to displace the binding of [3H]prazosin and to stimulate hydrolysis of phosphoinositides in the cerebral cortex of the rat. Both classes of alpha adrenoceptor compounds exhibited two sites of interaction with binding sites for [3H]prazosin in 30 mM Tris buffer. In a Na+ containing ionic buffer, the competition by phenylethylamines for [3H]prazosin sites shifted to a one-site best-fit, while imidazolines retained their two-site best-fit. Phenylethylamines stimulated hydrolysis of phosphoinositides in a dose-dependent manner, with ED50 values that correlated with Kd values from competition curves. In contrast, imidazolines were not potent or efficacious at stimulating hydrolysis of phosphoinositides and the binding affinities did not correlate with the ED50 values. The alpha 1 adrenoceptor antagonist, prazosin potently inhibited phenylethylamine, but not imidazoline-stimulated hydrolysis of phosphoinositides. Dose-response curves to the imidazoline, oxymetazoline, in the presence and absence of maximally stimulating concentrations of norepinephrine, indicated that oxymetazoline caused a dose-dependent inhibition of norepinephrine-stimulated hydrolysis of phosphoinositide. The inhibition of norepinephrine-stimulated hydrolysis of phosphoinositides was evident up to 100 microM, at which point oxymetazoline elicited hydrolysis of phosphoinositides through a non-alpha 1 adrenoceptor-mediated mechanism. These data indicate that imidazolines act primarily as antagonists at the alpha 1 adrenoceptor, coupled to hydrolysis of phosphoinositide and stimulate the hydrolysis of phosphoinositide through a non-alpha 1 adrenoceptor mechanism.

Animals↗
PubMed1991

Effects of ethanol on inositol 1,3,4,5-tetrakisphosphate metabolism by rat brain homogenates.

The hydrolysis of membrane phosphoinositides is widely recognized as an important signal transduction pathway in brain. One of the products of phosphoinositide hydrolysis, Ins(1,4,5)P3, is thought to participate in signal transduction by mobilizing intracellular calcium and it is now clear that Ins(1,4,5)P3 metabolism is a complicated process that may be highly regulated. In addition to being dephosphorylated by the action of a 5-phosphatase, Ins(1,4,5)P3 can be phosphorylated by a 3-kinase to Ins(1,3,4,5)P4. Although the physiological significance of the higher inositol polyphosphates is not clear, recent evidence suggests that Ins(1,3,4,5)P4 may also have important second messenger function. Since ethanol is known to have potent effects on synaptic transmission, we investigated the in vitro effects of ethanol on [3H]Ins(1,3,4,5)P4 metabolism by rat whole brain homogenates. Ins(1,3,4,5)P4 was rapidly hydrolyzed to Ins(1,3,4)P3, inositol bisphosphates [Ins(3,4)P2 and Ins(1,3)P2], inositol monophosphates [Ins(1)P/Ins(3)P and Ins(4)P], and to inositol by sequential dephosphorylation. No [3H]Ins(1,4,5)P3 was detected. Ethanol (500 mM), significantly accelerated the dephosphorylation of Ins(1,4,5)P3, resulting in a more rapid formation of inositol bisphosphates, monophosphates and inositol. However, intoxicating and sedative-hypnotic concentrations of ethanol (30-100 mM) had no effect upon Ins(1,3,4)P3 dephosphorylation, suggesting that pharmacologically relevant concentrations of ethanol do not directly effect the enzymes involved in the dephosphorylation of Ins(1,3,4,5)P4 to free inositol in brain.

Animals↗
PubMed1991

Effects of glucose on receptor-mediated phosphoinositide hydrolysis and second messenger generation in rat glomerular mesangial cells.

The phosphoinositide system plays a critical role in mesangial cell contraction. myo-Inositol depletion occurs in glomeruli from diabetic animals and may result in mesangial cell dysfunction. The hypothesis that mesangial cell exposure to high concentrations of glucose could lead to abnormalities in phosphoinositide metabolism and receptor-mediated inositol phosphate release was tested. When compared with controls (5 mM glucose), inositol phosphate release in mesangial cells exposed to 28 mM glucose was decreased by 27% after maximal stimulation with angiotensin II, by 41% after arginine vasopressin, and by 63% after the thromboxane A2 analog, U46619. Increasing the concentration of glucose to 50 mM caused a further reduction (from 27 to 54%) in maximal angiotensin II stimulation of inositol phosphate release. High glucose decreased incorporation of myo-inositol into phospholipids but did not change phosphoinositide mass. High glucose also resulted in increased de novo synthesis of diacylglycerol which was associated with membrane translocation of protein kinase C. myo-inositol supplementation prevented the reduction in phosphoinositide hydrolysis whereas sorbinil did not. It was concluded that high concentrations of glucose cause abnormalities in myo-inositol metabolism in mesangial cells which lead to reduced receptor-mediated phosphoinositide hydrolysis. These abnormalities appear to be related to desensitization of receptor-mediated phosphoinositide responses due to negative feedback by protein kinase C which becomes activated as a result of enhanced de novo diacylglycerol formation from glucose. These changes are unrelated to the polyol pathway and can be prevented by myo-inositol supplementation.

Animals↗
PubMed1990

Alpha 1-adrenergic receptors in the brain: characterization in astrocytic glial cultures and comparison with neuronal cultures.

Binding of [125I]HEAT to membranes prepared from primary cultures of astrocytic glial cells was time-dependent and 70-85% specific. Various adrenergic agonists and antagonists competed for [125I]HEAT binding according to the potencies of prazosin greater than, yohimbine greater than or equal to, clonidine, norepinephrine (NE), and propranolol. Scatchard analysis showed the Bmax of 209 fmol/mg protein and a Kd of 184 pM for [125I]HEAT binding by astrocytic glial membranes. Pretreatment of astrocytes with NE resulted in a dose-dependent downregulation of [125I]HEAT binding sites with a maximal response observed after 8 h at 100 microM NE. Removal of NE from cultures after pretreatment resulted in a time- and protein synthesis-dependent recovery of binding sites to control levels within 120 h. Incubation of astrocytic glial cultures with NE stimulated phosphoinositide (PI) hydrolysis in a time- and dose-dependent manner with a maximal stimulation of 2-fold observed in 60 min by 100 microM NE. Clonidine expressed differential effects on alpha 1-adrenergic receptors of the neuronal and astrocytic glial cultures. Pretreatment with 10 microM clonidine caused a 40% decrease in the Bmax of [125I]HEAT binding without influencing the Kd value in neuronal cultures. This downregulatory effect of clonidine was associated with a reduction in the ability of NE to stimulate PI hydrolysis in clonidine pretreated cells. In contrast to neuronal cultures, clonidine neither downregulated [125I]HEAT binding sites nor stimulated PI hydrolysis in glial cultures.

Adrenergic alpha-Agonists↗
PubMed1990

Receptors, phosphoinositol hydrolysis and plasticity of nerve cells.

Excitatory amino acid neurotransmission has been shown to be necessary but may not be sufficient, for the production of LTP and other prolonged changes in synaptic transmission. Excitatory neurotransmission may produce depolarization-induced increases in intracellular calcium that cause PI hydrolysis and synergistically potentiate receptor-G protein induced PI hydrolysis. This synergistic potentiation of phosphoinositide hydrolysis, and increased [Ca]i due to positive cross stimulation, may lead to depolarization block, a persistent increase in protein kinase activation, altered morphology, oncogene activity and other plasticity changes important in memory.

Animals↗
PubMed1990

Reduced alpha 1-adrenergic receptor-mediated inositide hydrolysis in cardiac atria of senescent rats.

We investigated the effect of age on epinephrine stimulation of phosphoinositide hydrolysis in atrial slices prepared from F-344 female rats. Three age groups were chosen for study: young adults (aged 6 months), mature adults (aged 15 months), and senescent animals (aged 25 months). Tissue slices were labeled with [3H]myoinositol and epinephrine-stimulated hydrolysis measured in the presence of LiCl. Epinephrine caused a dose-dependent increase in phosphoinositide hydrolysis in each age group. This increase was blocked by prazosin, suggesting that alpha 1-adrenergic receptors are involved. In animals aged 6 months, epinephrine caused a maximal increase in hydrolysis of 2.8-fold over basal. The maximal response was reduced at 15 months (2.52-fold increase, p less than 0.05) and at 25 months (2.02-fold increase, p less than 0.01). The potency for epinephrine stimulation of phosphoinositide hydrolysis was unchanged with age. The data indicate that alpha 1-mediated phosphoinositide hydrolysis in atria is reduced with age.

Aging↗
PubMed1990

Calcium- versus G protein-mediated phosphoinositide. Hydrolysis in rat cerebral cortical synaptoneurosomes.

The role of calcium and sodium in stimulating phosphoinositide hydrolysis in brain was investigated in rat cerebral cortical synaptoneurosomes. In buffer containing 136 mM sodium and various concentrations of added calcium (0-1.0 mM), basal, potassium-stimulated, and norepinephrine-stimulated formation of 3H-inositol phosphates decreased with decreasing extracellular calcium. Potassium- and norepinephrine-stimulated formation of 3H-inositol phosphates was reduced to basal levels by addition of EGTA. Isosmotically replacing sodium with choline chloride or N-methyl-D-glucamine to disrupt Na+/Ca2+ exchange resulted in a large increase in the formation of 3H-inositol phosphates. Measurement of cytosolic calcium with fura-2 revealed that the cytosolic calcium concentration was sensitive to changes in the extracellular calcium concentration and increased on resuspension of synaptoneurosomes in sodium-free rather than sodium-containing medium. In the absence of sodium, potassium-stimulated formation of 3H-inositol phosphates was reduced or eliminated, depending on the extracellular calcium concentration. Subtraction of basal formation of 3H-inositol phosphates from that in the presence of 1 mM carbachol or 100 microM norepinephrine revealed that the carbachol-stimulated component was the same in the presence and absence of sodium, whereas the norepinephrine-stimulated component was reduced in the absence of sodium. Addition of the protein kinase C activator 12-O-tetradecanoylphorbol 13-acetate inhibited norepinephrine- and, to a lesser extent, carbachol but not basal or aluminum fluoride-stimulated formation of 3H-inositol phosphates in sodium-free medium. These results suggest that an increase in intracellular calcium, via disruption of Na+/Ca2+ exchange or depolarization-induced calcium influx, may explain previous demonstrations that agents that stimulate Na+ influx can also stimulate phosphoinositide hydrolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Adenosine and its analogs stimulate phosphoinositide hydrolysis in the kidney.

Renal blood flow, glomerular filtration rate and sodium excretion are known to be affected by adenosine. The present studies were undertaken to investigate the actions of adenosine and its analogs (both agonists and antagonists) on phosphoinositide (PI) hydrolysis in the outer medullary slices. Adenosine was found to cause a dose-dependent stimulation of PI hydrolysis (ED50, 2.8 microM) in renal slices from outer medulla. The adenosine analogs 5'-(N-cyclopropyl)-carboxamidoadenosine (NCCA) and 5'-N-ethylcarboxamidoadenosine (NECA) also stimulated PI hydrolysis in renal medulla. Stimulation of PI hydrolysis was blocked by the adenosine antagonists: aminophylline, 1,3-dipropyl-7-methylxanthine (DMX) and 8-(p-sulfophenyl)-theophylline (8-SPT). Caffeine not only antagonized adenosine-stimulated PI hydrolysis but also increased PI hydrolysis independently. These results indicate that adenosine stimulates PI hydrolysis in renal medulla through a receptor-mediated mechanism.

Adenosine↗
PubMed1990

Desensitization of muscarinic stimulated hippocampal cell firing is related to phosphoinositide hydrolysis and inhibited by lithium.

The potency and efficacy of a series of muscarinic agonists for stimulation of neuronal firing rate was compared with stimulation of phosphoinositide (PPI) hydrolysis in similar hippocampal slice preparations. Carbachol, muscarine, pilocarpine, arecoline, bethanechol and oxotremorine varied in potency, but stimulated neuronal firing to a similar extent. At higher concentrations, all of the drugs except oxotremorine caused a decrease in firing rate (desensitization). A comparison of the concentration-response curves for PPI hydrolysis and neuronal firing rates showed that desensitization occurred at a threshold level of PPI hydrolysis. Although the concentration of drug that caused the decrease in firing rate was different for each agonist, the level of PPI hydrolysis at the desensitizing concentration was similar, with the exception of oxotremorine. Oxotremorine, the weakest agonist for stimulation of PPI hydrolysis, did not reach this PPI hydrolysis threshold and did not exhibit desensitization. Oxotremorine was also capable of both blocking and reversing the desensitization caused by carbachol. Low concentrations of pirenzepine, an M1 selective muscarinic antagonist, reversed carbachol desensitization. Concentrations of lithium that disrupt the phosphoinositide cycle by preventing recycling of free inositol (Allison, J. H., et al.: Biochem. Biophys. Res. Commun. 71: 664-670, 1976; Hallcher, L. M. and Sherman, W. R.: J. Biol. Chem. 225: 10896-10901, 1980) slowly reversed desensitization. Furthermore, inositol added to the buffer could re-establish desensitization in lithium-treated preparations. These studies suggest that muscarinic desensitization of hippocampal cell firing is related to large increases in phosphoinositide hydrolysis. Muscarinic receptor-stimulated increases in cell firing may be mediated by a subtype or state of muscarinic receptor different from that mediating phosphoinositide hydrolysis and desensitization.

Action Potentials↗
PubMed1989

Cholinergic receptors in renal medullary collecting duct cells.

Intrarenal administration of cholinergic agents produces diuresis. However, neither cholinergic innervation or specific cholinergic receptors have been shown to be present in the kidney. Recently, we have demonstrated that carbachol, a cholinergic agent, stimulates phosphoinositide hydrolysis in the inner medullary collecting duct (IMCD) cells. The effect was blocked by atropine (a cholinergic antagonist), suggesting that phosphoinositide hydrolysis occurs through the interaction of carbachol with specific cholinergic receptors in these cells. Therefore, we examined the cholinergic receptors in IMCD cells by measurement of radioligand binding of a cholinergic receptor antagonist, I-quinuclidinyl (phenyl-4-3H)benzilate([3H]QNB). The IMCD cells were prepared from rabbit kidneys by incubating the inner medullary slices with collagenase and treating the isolated cells with hypotonic solution to lyse cells other than IMCD cells. Binding of [3H]QNB to IMCD cells was measured at 37 degrees C for 60 min in the absence (total binding) and the presence (nonspecific binding) of 100 microM atropine (a muscarinic receptor antagonist). The specific binding (the difference between total and nonspecific binding) of [3H]QNB to IMCD cells was saturable with a Bmax (maximum binding sites) of 27.5 fmol/mg of protein and Kd (dissociation constant) of 0.27 nM. Atropine, but not hexamethonium (a nicotinic antagonist), was able to displace [3H]QNB from IMCD cells with a Ki of 0.1 microM. It is, therefore, concluded that specific high affinity muscarinic receptors are present in IMCD cells. These receptors may play a role in producing the pharmacologic actions of cholinergic agents on the kidney.

Animals↗
PubMed1988

Increased expression of alpha 1-adrenergic receptors in the hypothalamus of spontaneously hypertensive rats.

The specificity and molecular weights of alpha 1-adrenergic receptors in various tissues of spontaneously hypertensive (SH) rat were compared with normotensive controls (Wistar-Kyoto; WKY) with the use of [125I]HEAT and [125I]azidoprazosin, specific alpha 1-adrenergic receptor antagonists. Binding of [125I]HEAT to membranes prepared from SH rat brain hypothalamus was significantly higher, due to a 75% increase in the Bmax, than the WKY control. In contrast, the Bmax and Kd of [125I]HEAT binding to brainstem and liver membranes from SH rats were not significantly different from those of WKY controls. Competition-inhibition data suggested similar pharmacological specificity with potencies in the order of prazosin greater than yohimbine greater than propranolol for both WKY and SH rat membranes prepared from liver, hypothalamus, brainstem and neuronal cultures. Photoaffinity labeling of alpha 1-adrenergic receptors from hypothalamus, brainstem and neuronal cultures using [125I]azidoprazosin followed by SDS-PAGE and autoradiography showed the presence of one major band with a molecular weight (MW) of 105,000 Da for both WKY and SH rats. In contrast, labeling of liver alpha 1-adrenergic receptors revealed one major band with a MW of 60,000 Da. Quantitation of the 105,000-Da band from SH rat hypothalamic membranes demonstrated a 52% higher intensity compared with WKY controls. Neuronal cultures prepared from 1-day-old SH rats showed a similarly greater intensity of the 105,000-Da band compared with WKY controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗