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D C Klein

Publications and source records attributed to D C Klein.

At least 109 records · Page 6Linked to original sources
PubMed1988

Alpha 1-adrenergic potentiation of vasoactive intestinal peptide stimulation of rat pinealocyte adenosine 3',5'-monophosphate and guanosine 3',5'-monophosphate: evidence for a role of calcium and protein kinase-C.

alpha 1-Adrenergic agonists have recently been found to potentiate vasoactive intestinal peptide (VIP) stimulation of rat pinealocyte cAMP and cGMP. alpha 1-Adrenergic agonists also elevate pineal intracellular Ca2+ [( Ca2+]i) and activate protein kinase-C. In the present study, the possible involvement of Ca2+ and protein kinase-C in the alpha 1-adrenergic potentiation of VIP-stimulated cAMP and cGMP accumulation was examined with agents that alter [Ca2+]i or activate protein kinase-C. It was found that treatment with a Ca2+ chelator or with inorganic Ca2+ channel blockers inhibited alpha 1-adrenergic potentiation of VIP-stimulated cAMP and cGMP responses. Increasing [Ca2+]i by treatment with A23187, ouabain, or K+ potentiated VIP stimulation of cAMP and cGMP response. These observations indicate that Ca2+ mediates the alpha 1-adrenergic potentiation of VIP-stimulated cAMP and cGMP accumulation, as is true for the alpha 1-adrenergic potentiation of beta-adrenergic stimulated cAMP and cGMP accumulation. Activators of protein kinase-C mimicked the large effect alpha 1-adrenergic agonists have on cAMP accumulation in VIP-treated pinealocytes and had a small effect on cGMP accumulation in VIP-treated cells. These effects were not blocked by the Ca2+ chelator EGTA. However, the effects of a protein kinase-C activator on the cGMP response in VIP-stimulated cells were amplified by K+ (15 mM) or ouabain (1 microM), presumably through an action causing an increase in [Ca2+]i. These results suggest protein kinase-C is involved in the alpha 1-adrenergic potentiation of VIP-stimulated cAMP accumulation, as is the case for the alpha 1-adrenergic potentiation of beta-adrenergic stimulated cAMP. Protein kinase-C is also involved in cGMP accumulation, provided that there is a modest increase in [Ca2+]i.

Adrenergic alpha-Agonists↗
PubMed1988

Dual receptor regulation of cyclic nucleotides: alpha 1-adrenergic potentiation of vasoactive intestinal peptide stimulation of pinealocyte adenosine 3',5'-monophosphate.

The purpose of this investigation was to determine if alpha 1-adrenergic receptor activation would potentiate the vasoactive intestinal peptide (VIP)-stimulated increase in cAMP accumulation in the rat pinealocyte. Treatment with VIP alone increased cAMP accumulation less than 5-fold, and treatment with phenylephrine increased cAMP accumulation less than 2-fold. However, combined treatment with VIP and phenylephrine increased cAMP accumulation more than 20-fold. This is the first report that alpha 1-adrenergic and VIP receptors can interact to regulate cAMP in a cell of neural tube origin. The demonstration of such an integrated mechanism in pinealocytes is of special interest because VIP innervation of the pineal gland is of central origin, and adrenergic innervation is of peripheral origin. The magnitude of response makes the pinealocyte an attractive model for the study of such dual receptor regulation.

Animals↗
PubMed1988

Negative feedback mechanisms: evidence that desensitization of pineal alpha 1-adrenergic responses involves protein kinase-C.

alpha 1-Adrenergic stimulation of the pinealocyte translocates protein kinase-C, which, in turn, has an important positive effect on pineal cell function; translocation amplifies beta-adrenergic stimulation of both cAMP and cGMP. In the present report negative feedback effects of protein kinase-C are described, including inhibition of alpha 1-adrenergically induced increases in cytosolic Ca2+ ([Ca2+]i), phosphatidylinositol hydrolysis, and cGMP in beta-adrenergically stimulated cells. Time-course studies of cGMP and [Ca2+]i responses indicated that the onset of inhibition by the protein kinase-C activator 4 beta-phorbol 12-myristate 13-acetate (PMA) is rapid (less than 5 min). In contrast, PMA has no inhibitory effect on norepinephrine stimulation of cAMP accumulation or the induction of arylalkylamine N-acetyltransferase activity, a cAMP-dependent enzyme. This is consistent with the finding that PMA substitutes for the positive effect of alpha 1-activation and directly potentiates beta-adrenergic stimulation of cAMP production. Although PMA does inhibit alpha 1-adrenergic potentiation of cGMP in beta-adrenergically treated cells, it does not inhibit the potentiation of the cGMP response in beta-adrenergically stimulated cells produced by high K+, A23187, and ouabain, agents that translocate protein kinase-C secondary to elevation of [Ca2+]i. This suggests that translocation of protein kinase-C does not block an effect of Ca2+, but probably blocks an earlier step in adrenergic activation, presumably the alpha 1-adrenergic stimulation of [Ca2+]i. Finally, pretreatment of cells with an alpha 1-agonist markedly reduced cAMP and cGMP responses to subsequent beta-adrenergic stimulation. The data indicate that the following negative feedback mechanism is present in the pinealocyte: alpha 1-adrenoceptor-dependent elevation of [Ca2+]i----protein kinase-C translocation----inhibition of alpha 1-adrenergic dependent elevation of [Ca2+]i. This mechanism appears to function physiologically to provide a negative feedback signal which limits adrenergic responses that are dependent on an increase in [Ca2+]i, including the cAMP and cGMP increases.

Animals↗
PubMed1988

Submicrogram quantities of unstained proteins are visualized on polyvinylidene difluoride membranes by transillumination.

Unstained proteins on polyvinylidene difluoride membranes which have been dried and saturated with 20% methanol appear as clear areas when placed on a white light box. Sensitivity is comparable to that obtained with Coomassie Blue R250. This procedure greatly reduces the potential for unintended chemical modification during staining procedures, provides a nondestructive means of determining the major features of a protein pattern on a blot and makes it possible to initiate sequencing within minutes after blotting is complete.

Membranes, Artificial↗
PubMed1987

Developmental study of ouabain inhibition of adrenergic induction of rat pineal serotonin N-acetyltransferase (EC 2.3.1.87).

The activity of arylalkylamine N-acetyltransferase (EC 2.3.1.87), the rate-controlling enzyme in melatonin synthesis is stimulated approximately equal to 100-fold by an adrenergic cyclic AMP mechanism in both neonatal and adult rat pineal glands. This stimulation is blocked in the adult gland by the depolarizing agents ouabain (1 microM) and K+ (80 mM) (Parfitt, A., Weller, J.L., Klein, D.C., Sakai, K.K., and Marks, B.H. (1975) Mol. Pharmacol. 11, 241-255). In the present study pineal glands obtained from prenatal to adult rats were used; it was found that K+ (80 microM) inhibited the adrenergic stimulation of N-acetyltransferase activity at all ages but that ouabain (1 nM to 1 mM) treatment was not inhibitory early in development. In contrast, in the neonate, ouabain (1-100 nM) enhanced adrenergic induction of N-acetyltransferase activity, and ouabain treatment alone (1-1000 nM) stimulated N-acetyltransferase activity. A small stimulation was also seen at one concentration (1 nM) in the adult. Analysis of the development of high affinity ouabain binding sites and Na+,K+-ATPase activity in the intact pineal gland indicated that the developmental pattern of both resemble the development of ouabain inhibition of the adrenergic stimulation of N-acetyltransferase activity. All are low for the first few days of life, gradually increase during the next 3 weeks of life, and then approach adult levels. Similarly, ouabain (1 nM to 1 mM) had no effect on 86Rb uptake in the 2-day-old gland but blocked (IC50 congruent to 20 nM) 86Rb uptake in the adult gland. These findings indicate ouabain probably has little inhibitory effect on the norepinephrine stimulation of N-acetyltransferase activity in the neonatal because a high affinity ouabain binding form of Na+,K+-ATPase activity, similar to the alpha + form identified in rat brain, is at very low levels in the pinealocyte. Accordingly, it appears that an ouabain-insensitive mechanism in the neonatal gland maintains membrane potential and that this mechanism plays a less important role in the adult. The explanation of why ouabain alone stimulates N-acetyltransferase activity and why it enhances the effects of norepinephrine in the neonatal pineal gland might be that ouabain acts on surviving neural elements present in the gland to cause the net release of a transmitter, perhaps norepinephrine, which then stimulates N-acetyltransferase activity.

Acetyltransferases↗
PubMed1987

Ethanol inhibits dual receptor stimulation of pineal cAMP and cGMP by vasoactive intestinal peptide and phenylephrine.

Concurrent activation of vasoactive intestinal peptide and alpha 1-adrenergic receptor resulted in greater than 20-fold increases in pineal cAMP and cGMP accumulation. We now find that an intoxicating level of ethanol (0.2%, 34 mM) inhibits greater than 50% the large increases in pineal cAMP and cGMP produced by concurrent treatment with vasoactive intestinal peptide and phenylephrine. The potency of the various alcohols tested was directly related to their chain length. This inhibition appears to be specific since a five-fold higher concentration of ethanol does not inhibit the stimulation of cAMP and cGMP accumulation produced by concurrent treatment with isoproterenol and phenylephrine. Accordingly, it seems that one mechanism of action of ethanol on neural function may be its ability to selectively inhibit ethanol-sensitive integrative mechanisms which regulate cyclic nucleotides.

Alcohols↗
PubMed1987

Activation of alpha 1-adrenoceptors, protein kinase C, or treatment with intracellular free Ca2+ elevating agents increases pineal phospholipase A2 activity. Evidence that protein kinase C may participate in Ca2+-dependent alpha 1-adrenergic stimulation of pineal phospholipase A2 activity.

The regulation of pineal phospholipase A2 activity was studied indirectly by measuring the release of [3H]arachidonic acid from [3H]arachidonic acid-labeled tissue in organ culture and the formation of radiolabeled lysophosphatidylcholine by glands labeled with 32Pi or [14C]choline. Glands were transferred sequentially through a series of 10-min incubations in label-free medium. Norepinephrine (10(-5) M) stimulated [3H]arachidonic acid release by 2-fold; release peaked during the first 10 min and returned to basal levels during the third incubation period. Studies with selective alpha 1-, alpha 2-, and beta-adrenergic agents indicated that norepinephrine was acting through alpha 1-adrenergic receptors. Ca2+ appears to play a critical role because the effects of norepinephrine were mimicked by treatment with the Ca2+ ionophore A23187 and inhibited by inorganic Ca2+ channel blockers or EGTA; other [Ca2+]i elevating treatments also stimulated [3H]arachidonic acid release. The possibility that protein kinase C may be involved was studied because it is activated by the alpha 1-adrenergic agonist phenylephrine in the pineal gland (Sugden, D., Vanecek, J., Klein, D. C., Thomas, T. P., and Anderson, W. B. (1985) Nature 314, 359-361). Three protein kinase C activators stimulated [3H]arachidonic acid release with the same relative potency as that established for activation of protein kinase C (4 beta-phorbol 12-myristate 13-acetate greater than 4 beta-phorbol 12,13-dibutyrate greater than 1-oleoyl 2-acetylglycerol). The effects of norepinephrine, A23187, and protein kinase C activators appear to be mediated by phospholipase A2 because the effects of these compounds on [3H]arachidonic acid release are blocked by an established inhibitor of this enzyme, mepacrine, and because these compounds stimulate the formation of 32P- and 14C-labeled lysophosphatidylcholine by glands incubated with 32Pi or [14C]choline. In addition, an inhibitor of diacylglycerol lipase, another enzyme which generates arachidonic acid, did not inhibit the stimulation of [3H]arachidonic acid release by norepinephrine, A23187, or a phorbol ester. Cyclic nucleotides do not appear to play an important role in the regulation of phospholipase A2 activity because dibutyryl cyclic AMP does not alter [3H]arachidonic acid release and also because the amounts of cAMP and cGMP in the culture medium are not consistently associated with [3H]arachidonic acid release. These findings suggest that pineal phospholipase A2 activity is controlled by norepinephrine acting via an alpha 1-adrenergic mechanism which might involve Ca2+ and protein kinase C.

Adrenergic alpha-Agonists↗
PubMed1987

Transmembrane receptor cross-talk: concurrent VIP and alpha 1-adrenergic activation rapidly elevates pinealocyte cGMP greater than 100-fold.

The transmembrane regulation of cGMP accumulation, which is poorly understood, was studied using isolated rat pinealocytes. It was found for the first time that VIP stimulates cGMP accumulation several-fold. This stimulation was amplified by phenylephrine acting via alpha 1-adrenoceptors, resulting in a greater than 100-fold increase in cGMP accumulation. These results raise the possibility that cGMP accumulation in other tissues might be regulated by VIP, and that the stimulating effects of VIP might be markedly amplified by catecholamine transmitters in these tissues. It is also possible that other pairs of receptors might control large changes in cGMP in the central nervous system through parallel mechanisms.

Animals↗
PubMed1987

Protein kinase C is involved in adrenergic stimulation of pineal cGMP accumulation.

The amounts of cAMP and cGMP in the rat pinealocyte are regulated by norepinephrine acting through synergistic dual receptor mechanisms involving alpha 1- and beta-adrenoceptors (Vanecek, J., Sugden, D., Weller, J.L., and Klein, D.C. (1985) Endocrinology 116, 2167-2173; Sugden, L., Sugden, D., and Klein, D.C. (1986) J. Biol. Chem. 261, 11608-11612). Based on the available evidence, it appears that Ca2+-phospholipid-dependent protein kinase is involved in the alpha 1-adrenergic potentiation of beta-adrenergic stimulation of cAMP, but not in the stimulation of cGMP (Sugden, D., Vanecek, J., Klein, D.C., Thomas, T.P., and Anderson, W.B. (1985) Nature 314, 359-361). In the present study the role of protein kinase C in the adrenergic stimulation of cGMP was reinvestigated, with the purpose of determining whether protein kinase C activators would potentiate the effects of beta-adrenergic agonists on cGMP if cells were also treated with agents known to elevate intracellular free Ca2+. The protein kinase C activator 4 beta-phorbol 12-myristate 13-acetate (PMA) markedly elevated the cGMP content of beta-adrenergically stimulated pinealocytes which had also been treated with 1 microM A23187, 15 mM K+, or 1 microM ouabain. The effects of A23187 were blocked by EGTA and those of K+ were blocked by nifedipine, establishing the involvement of Ca2+. The stimulatory effects of PMA on cGMP accumulation were mimicked by other protein kinase C activators. PMA also stimulated cGMP accumulation in cells treated with cholera toxin (1 microgram/ml) and A23187 (1 microM), but not in cells treated only with cholera toxin. These results suggest that protein kinase C, which is activated in the pinealocyte by the alpha-adrenergic agonist phenylephrine, is probably involved in the adrenergic regulation of cGMP accumulation at a step distal to receptor activation.

Animals↗
PubMed1987

A cholera toxin substrate regulates cyclic GMP content of rat pinealocytes.

The adrenergic regulation of cyclic GMP in isolated pinealocytes was investigated. In this cell, norepinephrine stimulates cyclic GMP and cyclic AMP greater than 100-fold by activating both alpha 1- and beta-adrenoceptors. beta-Adrenergic activation is a requisite event and is potentiated by alpha 1-adrenergic activation (Vanecek, J., Sugden, D., Weller, J. L., and Klein, D. C. (1985) Endocrinology 116, 2167-2173). The current study found that cholera toxin could substitute for beta-adrenergic agonists in stimulating pinealocyte cyclic GMP content, as has been found to be the case for cyclic AMP. Treatment with cholera toxin alone (1 microgram/ml for 90 min) had a small effect (2- to 4-fold increase) on cyclic GMP; addition of the alpha 1-adrenergic agonists, phenylephrine, cirazoline, or methoxamine to cholera toxin-treated cells rapidly (peak at 5 min) caused a further 30- to 300-fold increase. The alpha 1-adrenergic agonists had little effect by themselves at concentrations which potentiated the effects of cholera toxin. The potentiating effect of phenylephrine was inhibited nearly completely by an alpha 1-adrenergic antagonist, but not by either an alpha 2- or beta-adrenergic antagonist. The purified cholera toxin subunits A and B did not stimulate cyclic GMP either alone or in the presence of phenylephrine. Furthermore, the potentiating action of phenylephrine was observed following 90 min but not 20 min of cholera toxin pretreatment. these results suggest that the regulation of cyclic GMP levels in the pineal gland involves an Ns-like GTP-binding regulatory protein. This is of interest because it is the first indication that cyclic GMP is regulated by such a GTP-binding protein in nonretinal tissue. It remains to be determined whether the mechanisms involved in the transmembrane regulation of cyclic AMP and cyclic GMP in any other tissue are similar.

Animals↗
PubMed1987

Inactivation of rat pineal hydroxyindole-O-methyltransferase by disulfide-containing compounds.

Rat pineal hydroxyindole-O-methyltransferase activity in crude homogenates is reduced by treatment with disulfides. Cystamine (IC50 = 128 microM) and selenocystamine (IC50 = 13 microM) are the most potent compounds tested. Reduced cystamine (cysteamine) and diaminohexane are inactive. N,N'-Diacetylcystamine, penicillamine disulfide, and glutathione disulfide are less potent or inactive; but several peptides (oxytocin, vasopressin, and arginine vasotocin) are active. Inactivation by cystamine is time- and temperature-dependent and is accelerated at higher pH. Disulfide treatment of intact pinealocytes also inactivates the enzyme. Addition of dithiothreitol during the enzyme assay completely reactivates inactivated enzyme formed by disulfide treatment of homogenates or intact cells. Rat hydroxyindole-O-methyltransferase is also inactivated in the absence of added disulfides and dissolved O2. This spontaneous inactivation is time-, temperature-, and pH-dependent and can be completely prevented, but not reversed, by dithiothreitol. In contrast to the inhibitory effects of cystamine on the rat enzyme, cystamine does not alter bovine hydroxyindole-O-methyltransferase and increases ovine hydroxyindole-O-methyltransferase activity. The bovine and ovine enzymes do not become inactive in the absence of added disulfides. Together these observations indicate that rat pineal hydroxyindole-O-methyltransferase can be inactivated by a protein thiol:disulfide exchange mechanism. This mechanism may contribute to the physiological regulation of this enzyme in the rat pineal gland but does not appear to be a common feature of pineal hydroxyindole-O-methyltransferase regulation in all species.

Acetylserotonin O-Methyltransferase↗
PubMed1987

Cardiac glycosides stimulate phospholipase C activity in rat pinealocytes.

Ouabain and related cardiac glycosides stimulate phospholipase C activity 5-fold in rat pinealocytes. The combined treatment of ouabain and norepinephrine, which also stimulates phospholipase C, produces an additive effect. The effects of either ouabain or norepinephrine are blocked by EGTA. However, there are notable differences. The stimulatory effect of ouabain is lost when extracellular Na+ is reduced to 20 mM and is not blocked by prazosin. In contrast, the stimulatory effect of norepinephrine is not blocked when extracellular Na+ is reduced to 20 mM but is blocked by prazosin. Ouabain appears to increase phospholipase C activity through a mechanism involving inhibition of Na+,K+-ATPase, and an accumulation of intracellular Na+ and Ca2+, not involving alpha 1-adrenoceptors. These findings raise the possibility that activation of phospholipase C might be a more general effect of cardiac glycosides.

Animals↗
PubMed1987

Alpha 1-adrenoceptor activation elevates cytosolic calcium in rat pinealocytes by increasing net influx.

The regulation of [Ca2+]i in rat pinealocytes was studied using the fluorescent indicator quin2. Pinealocyte resting [Ca2+]i was approximately 100 nM; this rapidly decreased in low Ca2+ medium (approximately 10 microM), indicating there was a high turnover of [Ca2+]i in these cells. Norepinephrine (NE, 10(-6) M) increased [Ca2+]i to approximately 350 nM within 1 min; [Ca2+]i then remained elevated for 30 min. The relative potency of adrenergic agonists was NE greater than phenylephrine much greater than isoproterenol. Phentolamine (10(-6) M) and prazosin (10(-8) M) blocked the effects of adrenergic agonists; in contrast, propranolol (10(-6) M) or yohimbine (10(-6) M) had little or no effect. These observations indicate NE acts via alpha 1-adrenoceptors to elevate [Ca2+]i. The [Ca2+]i response to NE did not occur when [Ca2+]e was reduced to approximately 10 microM by adding EGTA 5s before NE, indicating an increase in net Ca2+ influx is involved rather than mobilization of Ca2+ from intracellular stores. The effect of NE was not blocked by nifedipine (10(-6) M), which did block a K+-induced increase in [Ca2+]i, presumably involving voltage-sensitive channels. Ouabain (10(-5) M) caused a gradual increase in [Ca2+]i; this increase was not blocked by nifedipine. Together these data indicate that pinealocyte [Ca2+]i may be influenced by mechanisms regulated by alpha 1-adrenoceptors, voltage-dependent Ca2+ channels, and perhaps a Na+/Ca2+ exchange mechanism stimulated by ouabain. These studies indicate that the pinealocyte is an interesting model to use to study the adrenergic regulation of [Ca2+]i because of the rapid and prolonged changes in [Ca2+]i produced by alpha 1-adrenoceptor activation.

Aminoquinolines↗
PubMed1987

Stimulation of the paraventricular nucleus area of the hypothalamus elevates urinary 6-hydroxymelatonin during daytime.

The paraventricular nucleus of the hypothalamus (PVN) is thought to be a part of the neural circuit comprising the melatonin rhythm generating system (MRGS). Electrical stimulation of the PVN during the early lights-on period significantly elevated urinary 6-hydroxymelatonin content to nearly 50% of night levels; stimulation during the lights-off period did not produce significant changes. In contrast to the effects of PVN stimulation, stimulation of surrounding brain areas was without effect at either time. This observation confirms the participation of the PVN in the MRGS.

Animals↗
PubMed1987

A simple and rapid method for the purification of ovine pineal arylalkylamine N-acetyltransferase.

A two-step chromatographic procedure has been developed for the purification of ovine pineal arylalkylamine N-acetyltransferase (EC 2.3.1.87), based on the principles of disulfide exchange and anion exchange. The enzyme from 20 ovine pineal glands can be purified about 500-fold in a day; recovery is about 5%. Polyacrylamide gel electrophoretic analysis of the final preparation shows four major bands; one appears to be arylalkylamine N-acetyltransferase.

Acetyltransferases↗
PubMed1987

Phosphatidylinositol phosphodiesterase (phospholipase C) activity in the pineal gland: characterization and photoneural regulation.

Phosphatidylinositol phosphodiesterase (PL-C) appears to be a key element in the adrenergic regulation of pineal cyclic AMP levels. In the present study, the rat pineal enzyme was characterized using exogenous [3H]phosphatidylinositol (0.5 mM) as substrate. Half the enzyme activity was found in the cytosolic fraction, but the highest specific concentration was associated with the membrane fraction. Two pH optima (5.5 and 7.5) of enzyme activity were observed for the membrane fraction but only one in the cytosol fraction (pH 5.5). Enzyme activity in both fractions was Ca2+ dependent. In the case of the membrane protein in pH 7.5, the enzyme activity was sensitive to changes in Ca2+ in the 10-100 nM range. Addition of an equimolar concentration of phosphatidylinositol 4-phosphate nearly completely inhibited the hydrolysis of [3H]phosphatidylinositol; other phospholipids (1.0 mM) were less potent. This may reflect our present finding that [3H]phosphatidylinositol 4-phosphate is a better substrate than [3H]phosphatidylinositol for the enzyme. Stimulus deprivation (2 weeks of constant light or superior cervical ganglionectomy) reduced the cytosolic activity by 30% and had no effect on the membrane-associated enzyme.

Animals↗