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Biomedical subjects

R D Harvey

Publications and source records attributed to R D Harvey.

At least 19 recordsLinked to original sources
PubMed2001

Role of tyrosine kinase activity in alpha-adrenergic inhibition of the beta-adrenergically regulated L-type Ca(2+) current in guinea-pig ventricular myocytes.

1. The purpose of this study was to investigate the hypothesis that tyrosine kinase activity contributes to alpha(1)-adrenergic inhibition of beta-adrenergic responses in cardiac myocytes. We addressed this question by studying the pharmacological regulation of the L-type Ca(2+) current in acutely isolated adult guinea-pig ventricular myocytes using the whole-cell patch-clamp technique. 2. The selective alpha(1)-adrenergic receptor agonist methoxamine had no effect on the basal L-type Ca(2+) current. Methoxamine also had no effect on cAMP-dependent stimulation of the Ca(2+) current mediated by H(2) histamine receptor activation. However, methoxamine did inhibit cAMP-dependent stimulation of the Ca(2+) current mediated by beta-adrenergic receptor activation. The ability of methoxamine to inhibit beta-adrenergic regulation of the Ca(2+) current was significantly antagonized by the tyrosine kinase inhibitors genistein and lavendustin A. 3. The inhibitory effect of methoxamine was also mimicked by the phosphotyrosine phosphatase inhibitor pervanadate (PVN). PVN had no effect on basal Ca(2+) current or Ca(2+) current stimulated by histamine, but it did inhibit Ca(2+) current stimulated by beta-adrenergic receptor activation. Furthermore, the ability of PVN to inhibit beta-adrenergic stimulation of the Ca(2+) current was antagonized by lavendustin A. 4. These results are consistent with the conclusion that in guinea-pig ventricular myocytes alpha-adrenergic inhibition of beta-adrenergic responses involves a tyrosine kinase-dependent signalling pathway. The fact that methoxamine and PVN antagonized cAMP-dependent responses mediated by beta-adrenergic, but not H(2) histamine, receptor activation suggests that the inhibitory effect of alpha-adrenergic stimulation and tyrosine kinase activity is at the level of the beta-adrenergic receptor.

Adrenergic alpha-Agonists↗
PubMed2001

ACh-induced rebound stimulation of L-type Ca(2+) current in guinea-pig ventricular myocytes, mediated by Gbetagamma-dependent activation of adenylyl cyclase.

1. The effects that muscarinic receptor stimulation have on the cAMP-dependent regulation of L-type Ca(2+) currents were studied in isolated guinea-pig ventricular myocytes using the whole-cell configuration of the patch-clamp technique. 2. The muscarinic agonist ACh inhibited the Ca(2+) current stimulated by the beta-adrenergic agonist isoprenaline (Iso), and washout of ACh revealed a stimulatory response that appeared as a transient rebound increase in the amplitude of the Ca(2+) current. The ACh-induced stimulatory effect was not observed in the absence of Iso. 3. ACh-induced rebound stimulation was also observed in the presence of H(2) histamine receptor activation and cholera toxin treatment, which like beta-adrenergic receptor activation enhance adenylyl cyclase (AC) activity in a stimulatory G protein (G(s))-dependent manner. ACh-induced rebound stimulation was not observed in the presence of forskolin, which enhances AC activity in a G(s)-independent manner. 4. Pertussis toxin (PTX) treatment blocked both the stimulatory and inhibitory effects of ACh. Intracellular dialysis with QEHA, a peptide that binds free G protein betagamma subunits, selectively antagonized the stimulatory effect, leaving an enhanced inhibitory effect. 5. Evidence for the expression of AC4, an isoform of AC that can be stimulated by Gbetagamma but only in the presence of Galpha(s), was obtained by Western blot analysis of guinea-pig ventricular myocyte membrane preparations. 6. These results suggest that muscarinic receptor stimulation facilitates as well as inhibits cAMP-dependent regulation of the Ca(2+) current and that the net response is a balance between these two actions. We suggest that the stimulatory effect is due to a direct activation of AC4 by the betagamma subunits of a PTX-sensitive G protein.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2001

Brain metastases.

Metastatic tumors to the brain are an increasing cause of morbidity and mortality in patients with systemic cancers. Many new therapies used to treat systemic cancers do not penetrate the central nervous system (CNS) and do not protect patients from the development of brain metastases. Surgery, radiosurgery, and radiation therapy are all used to treat brain metastases. It is in our opinion a mistake to use only one or two of these modalities to the exclusion of other(s). The role of systemic chemotherapy is still limited, due to both the issues of drug delivery caused by the blood brain barrier and to the relative resistance of many of these tumors to chemotherapy. Traditionally, brain metastases have been grouped together regardless of the origin of the tumor and have been treated with a single algorithm. As we encounter more patients for whom treatment of the brain metastases is an important determinant of survival, we must tailor our treatment strategies to individual tumor types. Also, we must recognize differences in each tumor's sensitivity to chemotherapy and radiotherapy and differences in their biology.

Adult↗
PubMed2001

Individual differences in the phenomenological impact of social stigma.

In an attempt to define stigmatization from the perspective of stigmatized group members, the author focused on the development and validation of a stigmatization scale. The scale's content validity was established with the assistance of experts in the field. European American, African American, and Native American students from 5 different U.S. universities completed the Stigmatization Scale. The construct validity of the scale was suggested by its convergence with similar measures of social alienation and its divergence from measures of personal subjective well-being. The finding that both the African American and Native American students reported significantly higher stigmatization scores than did the European Americans indicated the scale's known-groups validity. African American students at a predominantly Black university reported lower stigmatization than did African American students at a predominantly White university, suggesting the scale's malleability to context.

Adult↗
PubMed2000

Muscarinic inhibitory and stimulatory regulation of the L-type Ca2+ current is not altered in cardiac ventricular myocytes from mice lacking endothelial nitric oxide synthase.

Using conventional and perforated patch-clamp techniques, the inhibitory and stimulatory effects of acetylcholine (ACh) on beta-adrenergic regulation of the L-type Ca2+ current (ICa) were studied in ventricular myocytes from wild-type mice (WT) and from mice lacking endothelial nitric oxide synthase (eNOS or NOS3; NOS3-KO mice). To validate the direct comparison of ACh effects on beta-adrenergic responses, the sensitivity of ICa to the beta-adrenergic agonist isoprenaline (Iso) was studied in both WT and NOS3-KO mouse myocytes. ICa sensitivity to Iso was not found to be significantly different in WT and NOS3-KO myocytes: Iso increased ICa with an EC50 of 4.9 and 3.7 nM in WT and NOS3-KO myocytes, respectively. ACh-induced inhibition of ICa did not significantly differ in ventricular myocytes from WT and NOS3-KO mice. ACh (10 microM) inhibited the stimulatory effect of 3 nM Iso by 39 and 35% in WT and NOS3-KO myocytes, respectively. Exposure to and subsequent washout of ACh in the continuous presence of submaximally stimulating concentrations of Iso (1-3 nM) resulted in a transient rebound stimulation of ICa in both WT and NOS3-KO mouse myocytes. The magnitude of the stimulatory effect of ACh did not significantly differ in WT and NOS3-KO mice. These results indicate that nitric oxide (NO) generated by NOS3 does not significantly affect the beta-adrenergic responsiveness of ICa. The results also confirm previous work indicating that NO generated by NOS3 is not obligatory for muscarinic inhibition of the beta-adrenergically regulated ICa in ventricular myocytes. Finally these results demonstrate for the first time that NO generated by NOS3 is not involved in muscarinic rebound stimulation of ICa in ventricular myocytes.

Acetylcholine↗
PubMed2000

Tyrosine phosphatase inhibitors selectively antagonize beta-adrenergic receptor-dependent regulation of cardiac ion channels.

beta-Adrenergic receptor stimulation regulates the activity of several different cardiac ion channels through an adenylate cyclase/cAMP/protein kinase A-dependent mechanism. Previous work has suggested that basal tyrosine kinase activity attenuates the beta-adrenergic responsiveness of these cardiac ion channels, supporting the idea that tyrosine phosphorylation exerts an inhibitory effect at some point in the common signaling pathway. To determine which element in the beta-adrenergic pathway is regulated by tyrosine kinase activity, we studied the effects of various protein tyrosine phosphatase (PTP) inhibitors on the cAMP-dependent regulation of the L-type Ca(2+) current in guinea pig ventricular myocytes. Three such compounds, sodium orthovanadate, peroxovanadate, and bpV(phen), had no effect on the basal Ca(2+) current, yet each caused a pronounced inhibition of the Ca(2+) current stimulated by the beta-adrenergic receptor agonist isoproterenol. These observations are consistent with the idea that basal tyrosine kinase activity is capable of inhibiting beta-adrenergic responses. However, these PTP inhibitors had no effect on cAMP-dependent stimulation of the Ca(2+) current via activation of adenylate cyclase with forskolin or activation of H(2)-histaminergic receptors with histamine. These results are consistent with the idea that inhibition of PTP activity produces an inhibitory effect involving a tyrosine kinase-dependent mechanism acting selectively at the level of the beta-adrenergic receptor. This signaling mechanism does not seem to be linked to tyrosine kinase activity associated with insulin and insulin-like growth factor receptors, because acute exposure to agonists of these receptors did not inhibit isoproterenol regulation of the Ca(2+) current.

Animals↗
PubMed1998

Genistein increases the sensitivity of cardiac ion channels to beta-adrenergic receptor stimulation.

The whole-cell patch-clamp technique was used to monitor the effects of genistein, a tyrosine kinase inhibitor, on membrane currents recorded from isolated guinea pig ventricular myocytes. Under control conditions, genistein (50 micromol/L) did not activate the latent cAMP-regulated Cl- current (ICl). However, in the presence of a subthreshold concentration (1 nmol/L) of the beta-adrenergic agonist isoproterenol (Iso), genistein caused a near-maximal activation of this current. In the absence of genistein, Iso activated ICl with an EC50 of 5 nmol/L. In the presence of genistein, Iso activated ICl with an EC50 of 0.3 nmol/L. This facilitatory effect was not observed in the presence of daidzein (50 micromol/L), an analogue of genistein that only weakly inhibits tyrosine kinase activity. Furthermore, peroxovanadate, a potent inhibitor of phosphotyrosine phosphatase activity, inhibited ICl activated by Iso alone, and it blocked the stimulatory effect of genistein in the presence of Iso. To determine whether the stimulatory effect of genistein was specific for ICl, we also studied its action on the cAMP-regulated delayed rectifier K+ current (IK) and L-type Ca2+ current (ICa-L) present in these cells. Basal IK and ICa-L were partially (approximately 30% to 40%) inhibited by genistein. However, this inhibitory effect was mimicked by daidzein, suggesting that inhibition of tyrosine kinase activity is not involved. In addition to the nonspecific inhibitory effect, genistein also caused a significant increase in the beta-adrenergic sensitivity of the unblocked cationic currents. In the absence of genistein, 1 nmol/L Iso had no effect on either IK or ICa-L. However, in the presence of genistein, 1 nmol/L Iso significantly increased the magnitude of both currents. These results suggest that tyrosine kinase activity may play an important role in regulating beta-adrenergic responsiveness of the heart.

Adrenergic beta-Agonists↗
PubMed1998

Cushing's disease treated by trans-sphenoidal selective adenomectomy in mid-pregnancy.

The clinical course and diagnosis of a patient with Cushing's disease complicated by pregnancy is described, and the anaesthetic management of trans-sphenoidal selective adenomectomy performed during the second trimester outlined. Problems included obesity, diabetes, hypertension and a suboptimal airway. Fibreoptic awake intubation and intravenous anaesthesia were used. Insulin requirements decreased substantially after surgery. Early administration of hydrocortisone after surgery avoided the risk of an addisonian crisis but delayed biochemical confirmation of a metabolic cure.

Adenoma↗
PubMed1998

PKC regulation of cardiac CFTR Cl- channel function in guinea pig ventricular myocytes.

The role of protein kinase C (PKC) in regulating the protein kinase A (PKA)-activated Cl- current conducted by the cardiac isoform of the cystic fibrosis transmembrane conductance regulator (cCFTR) was studied in guinea pig ventricular myocytes using the whole cell patch-clamp technique. Although stimulation of endogenous PKC with phorbol 12,13-dibutyrate (PDBu) alone did not activate this Cl- current, even when intracellular dialysis was limited with the perforated patch-clamp technique, activation of PKC did elicit a significant response in the presence of PKA-dependent activation of the current by the beta-adrenergic receptor agonist isoproterenol. PDBu increased the magnitude of the Cl- conductance activated by a supramaximally stimulating concentration of isoproterenol by 21 +/- 3.3% (n = 9) when added after isoproterenol and by 36 +/- 16% (n = 14) when introduced before isoproterenol. 4alpha-Phorbol 12, 13-didecanoate, a phorbol ester that does not activate PKC, did not mimic these effects. Preexposure to chelerythrine or bisindolylmaleimide, two highly selective inhibitors of PKC, significantly reduced the magnitude of the isoproterenol-activated Cl- current by 79 +/- 7.7% (n = 11) and 52 +/- 10% (n = 8), respectively. Our results suggest that although acute activation of endogenous PKC alone does not significantly regulate cCFTR Cl- channel activity in native myocytes, it does potentiate PKA-dependent responses, perhaps most dramatically demonstrated by basal PKC activity, which may play a pivotal role in modulating the function of these channels.

Adrenergic beta-Agonists↗
PubMed1997

Rebound stimulation of the cAMP-regulated Cl- current by acetylcholine in guinea-pig ventricular myocytes.

1. Acetylcholine (ACh)-induced rebound stimulation of the cAMP-regulated Cl- current was studied in isolated guinea-pig ventricular myocytes using dialysing and dialysis-limiting configurations of the whole-cell patch-clamp technique. 2. Exposure to and subsequent washout of ACh produced a transient rebound stimulation of the Cl- current. However, this rebound response was only observed in the presence of submaximally stimulating concentrations of the cAMP-producing agonists isoprenaline (Iso) or histamine. ACh-induced rebound stimulation was not observed in the presence of maximally stimulating concentrations of Iso, nor was it observed in the absence of Iso. 3. To prevent saturation of responses during rebound, the effects of ACh were studied in the presence of a subthreshold concentration of Iso (0.001 microM). Varying the duration of exposure to ACh before washout demonstrated that the stimulatory effect of 1 microM ACh approaches steady state with a time constant of 34 s. Exposing myocytes to varying concentrations of ACh for 90 s demonstrated that the EC50 for the stimulatory effect of ACh was 0.15 microM with a maximum response equal to 67% of that obtained by a maximally stimulating concentration of Iso alone. 4. Rebound stimulation of the Cl- current could also be elicited by washing in 2 microM atropine during exposure to ACh, instead of washing out ACh. Furthermore, ACh-induced rebound was blocked by the M2 muscarinic receptor antagonist methoctramine but not by the M1 receptor antagonist pirenzepine. Rebound was also blocked in pertussis toxin (PTX)-treated myocytes. 5. ACh-induced rebound stimulation was not blocked by: (a) L-NMMA, an inhibitor of nitric oxide synthase activity; (b) Methylene Blue, LY-83583, and ODQ, inhibitors of cGMP production; or (c) milrinone, an inhibitor of cGMP-dependent phosphodiesterase activity. 6. These results indicate that ACh can stimulate cAMP-regulated ion channel activity in cardiac ventricular myocytes by facilitating beta-adrenergic and histaminergic responses. This is opposite to the inhibitory actions more typically associated with muscarinic receptor stimulation in ventricular myocardium. This stimulatory effect of ACh is mediated through M2 muscarinic receptors and a PTX-sensitive G-protein, but it does not appear to involve the production of nitric oxide or cGMP.

Acetylcholine↗
PubMed1997

Pharmacological evidence that calcium is not required for P2-receptor-stimulated Cl- secretion in HT29-Cl.16E.

Extracellular ATP at micro- to millimolar concentrations activates Cl- conductance and increases cytosolic calcium ([Ca]i) in many epithelial cells, including the colonic epithelial cell line HT29-Cl. 16E. Therefore, [Ca]i has been postulated to be the intracellular messenger for Cl- channel activation. HT29-Cl.16E is a highly differentiated cell line that forms confluent monolayers and secretes mucins and Cl-. The involvement of [Ca]i in the purinergically-stimulated Cl- secretion was investigated pharmacologically in this cell line by whole-cell patch-clamp and Ussing chamber techniques, as well as [Ca]i measurements in fura-2 loaded cells. The calmodulin inhibitors W13 (5 microm) and chlorpromazine (50 microm) abolished increases in ATP-stimulated [Ca]i-increases by 90% and 80%, respectively. However, these inhibitors had no effect on the ATP-stimulated Cl- conductance measured in either individual cells or confluent monolayers. As controls, the effects of W13 and chlorpromazine on Ca2+-ionophore stimulated Cl- conductance was measured. In this case, the two compounds inhibited whole cell Cl- conductance and monolayer Isc by 90% and 100%, respectively. These data demonstrate: (1) The purinergically-stimulated increase in Cl- current does not require an increase in [Ca]i, suggesting the involvement of either another signaling pathway or direct activation of Cl- channels by purinergic receptors. (2) A calmodulin or a calmodulinlike binding site that is sensitive to W13 and chlorpromazine participates in the regulation of the [Ca]i increase by purinergic receptors in HT29-Cl.16E.

Calcium↗
PubMed1997

Role of G proteins in alpha1-adrenergic inhibition of the beta-adrenergically activated chloride current in cardiac myocytes.

alpha1-Adrenergic receptor stimulation can inhibit the Cl- current activated by beta-adrenergic receptor agonists in guinea-pig ventricular myocytes. We investigated the role of G proteins in mediating this type of alpha-adrenergic response. The combined alpha- and beta-adrenergic agonist norepinephrine (NE) activated the Cl- current with an EC50 value of 53 nM. Preincubation of myocytes with PTX decreased the EC50 value for NE activation of the Cl- current to 5.9 nM, and addition of the alpha1-adrenergic receptor antagonist prazosin did not cause any further change in sensitivity to NE. These results suggest that the alpha1-adrenergic inhibition of beta-adrenergic responses is mediated through a PTX-sensitive G protein. However, PTX pretreatment also increased the sensitivity of the Cl- current to the selective beta-adrenergic agonist isoproterenol (Iso), which indicates that the PTX treatment increases the sensitivity to beta-adrenergic stimulation alone and that this could account for the PTX-induced change in sensitivity to NE. Consistent with this idea, the selective alpha1-adrenergic receptor agonist methoxamine was still able to inhibit the Cl- current activated by Iso in PTX-treated myocytes. However, the sensitivity to methoxamine was significantly decreased. In control cells, the Cl- current activated by 30 nM Iso was inhibited by methoxamine with an EC50 value of 8.3 microM, but in PTX-treated cells, the EC50 value was 284 microM. The EC50 for methoxamine inhibition was similarly increased when the Cl- current was activated by 300 nM Iso. These data suggest that the effects of PTX on alpha1-adrenergic responses can actually be explained by changes in the sensitivity to beta-adrenergic stimulation. To verify the role for a G protein in mediating the inhibitory alpha1-adrenergic response, we examined the effect of methoxamine on the Cl- current activated in cells dialyzed with the nonhydrolyzable GTP analogue guanosine-5'-O-(3-thio)triphosphate. Pre-exposure to methoxamine resulted in an attenuated response upon subsequent exposure to Iso alone. We conclude that alpha1-adrenergic inhibition of beta-adrenergic responses is mediated by a G protein-dependent mechanism that appears to be PTX-insensitive.

Adrenergic alpha-Antagonists↗
PubMed1997

Role of beta1- and beta2-adrenergic receptors in regulation of Cl- and Ca2+ channels in guinea pig ventricular myocytes.

The role of beta1- and beta2-adrenergic receptor stimulation in modulating adenosine 3',5'-cyclic monophosphate (cAMP)-regulated Cl- and Ca2+ currents was investigated with use of guinea pig ventricular myocytes. Activation of the Cl- current by the nonselective beta-receptor agonist isoproterenol (Iso) was not affected by the beta2-receptor antagonist ICI-118,551 (ICI), but it was blocked by the beta1-receptor antagonist atenolol. The inability of beta2-receptor stimulation to activate the Cl- current was confirmed by the lack of response to the selective beta2-receptor agonists salbutamol and zinterol. Responses to beta2-adrenergic receptor stimulation were also looked for in pertussis toxin (PTX)-treated myocytes because PTX increases the sensitivity of responses to Iso, and PTX has been reported to increase the responsiveness to beta2- but not beta1-receptor stimulation. PTX treatment increased the sensitivity of the Cl- current to activation by Iso in the presence of ICI, indicating that PTX increases beta1-receptor responsiveness. PTX treatment also resulted in the ability of salbutamol to activate the Cl- current. However, the response to salbutamol was blocked by atenolol but not by appropriate concentrations of ICI, suggesting that salbutamol was activating beta1-receptors. These results indicate that PTX treatment increases the sensitivity to beta1-receptor stimulation, without affecting beta2-responsiveness. To verify that the lack of response to beta2-receptor stimulation was not unique to the Cl- current, the effects of beta2-receptor agonists on the L-type Ca2+ current were also examined. The Ca2+ current was only affected by high concentrations of zinterol or salbutamol, and such responses were blocked by atenolol, but not by ICI, suggesting that activation of beta1-receptors was involved. These results indicate that beta1- but not beta2-adrenergic receptor stimulation plays an important role in modulating the cAMP-regulated Cl- and Ca2+ currents in guinea pig ventricular myocytes.

Adrenergic beta-Agonists↗
PubMed1996

Nitric oxide synthase activity in guinea pig ventricular myocytes is not involved in muscarinic inhibition of cAMP-regulated ion channels.

It has recently been demonstrated that NO plays an obligatory role in muscarinic inhibition of beta-adrenergically stimulated ion channels in cardiac sinoatrial node cells (J Gen Physiol. 1995;106:45-65). We looked for evidence that NO might play a similar role in ventricular cells by using histochemical staining for NO synthase (NOS) activity and whole-cell patch-clamp recording of cAMP-regulated Cl- currents. Myocytes isolated from guinea pig hearts stained positively for NADPH-diaphorase activity, suggesting that these cells do express NOS. Acetylcholine (ACh) inhibition of the R(-)-isoproterenol bitartrate (Iso)-activated Cl- current was also reversed by the cGMP-lowering agents LY-83583 and methylene blue, consistent with idea that NO activation of guanylate cyclase may contribute to muscarinic responses. However, LY-83583 and methylene blue activated the Cl- current in the presence of subthreshold concentrations of Iso alone, suggesting that their effects may not be due to antagonism of an NO/cGMP-dependent response. Furthermore, ACh inhibition of Iso-activated Cl- currents could not be mimicked by the NO donors sodium nitroprusside,3-morpholinosydnonimine, and spermine-NO. Similarly, ACh inhibition of the Iso-activated Cl- current could not be blocked by the NOS inhibitor NG-monomethyl-L-arginine. These results indicate that even though ventricular myocytes possess NOS activity, NO production does not play an important role in muscarinic inhibition of beta-adrenergically regulated Cl- channels in these cells.

Acetylcholine↗
PubMed1996

Alpha 1-adrenergic inhibition of the beta-adrenergically activated Cl- current in guinea pig ventricular myocytes.

alpha-Adrenergic receptor stimulation regulates the activity of a number of different cardiac ion channels, including those underlying one or more distinct Cl- conductances. The whole-cell patch-clamp technique was used in the present study to investigate the effects of alpha-adrenergic stimulation on the beta-adrenergically regulated Cl- current in guinea pig ventricular myocytes. Neither alpha 1-adrenergic receptor stimulation with methoxamine (25 to 500 mumol/L) nor direct activation of endogenous protein kinase C (PKC) with phorbol 12,13-dibutyrate (PDBu, 100 nmol/L) evoked a Cl- current. On the contrary, the Cl- current activated by 30 nmol/L isoproterenol was inhibited by methoxamine, with an EC50 of 6.7 +/- 2.6 mumol/L, and this response was blocked by prazosin, an alpha 1-adrenergic receptor antagonist. Prazosin also decreased the EC50 for current activation by norepinephrine from 53 +/- 7.1 to 18 +/- 3.8 nmol/L, demonstrating that the ability of this endogenous neurotransmitter to activate the Cl- current through beta-adrenergic receptor stimulation is limited by its intrinsic ability to also activate alpha-adrenergic receptors. Methoxamine did not inhibit the Cl- current evoked by either direct activation of adenylate cyclase with forskolin or inhibition of phosphodiesterase activity with 3-isobutyl-1-methylxanthine, indicating that alpha-adrenergic stimulation inhibits beta-adrenergic responses at a point upstream of adenylate cyclase activation. Methoxamine also did not inhibit the Cl- current activated by histamine, suggesting that alpha-adrenergic stimulation specifically inhibits beta-adrenergic receptor-mediated responses. The inhibitory effect of methoxamine was not mimicked by PDBu, and it persisted in the presence of bisindolylmaleimide, a selective PKC inhibitor. However, methoxamine inhibition of the isoproterenol-activated Cl- current was sensitive to pertussis toxin. These results suggest that alpha-adrenergic receptor stimulation inhibits the beta-adrenergically activated Cl- current, demonstrating a novel mechanism by which alpha-adrenergic receptors may regulate ion channel activity in the heart.

Animals↗
PubMed1995

Acute pre-tibial myxoedema following radioiodine therapy for thyrotoxic Graves' disease.

A 54-year-old woman was treated with an oral dose of 555MBq of 131I radioiodine for thyrotoxicosis. She had no clinically detectable extrathyroidal manifestations of Graves' disease at the time, but within two months developed moderately severe ophthalmopathy and very extensive thyroid dermopathy affecting her face, arms, hands and feet, in addition to the classic pre-tibial area. Although she developed mild post radioiodine hypothyroidism, this was detected at an early stage and its treatment had no effect on the extrathyroidal signs. Thyrotrophin receptor antibodies (TRAb) were positive before treatment (22% inhibition of TSH binding in neat serum), rose to very high levels following radioiodine (97.6% inhibition), and fell progressively over the following year during treatment with prednisolone. Thyroglobulin autoantibodies became detectable following radioiodine but thyroid peroxidase antibodies were undetectable throughout. Serum and purified IgG from blood samples obtained prior to steroid therapy and over the subsequent year were tested on a dermal fibroblast cell line in vitro for the stimulation of synthesis of glycosaminoglycans, protein and DNA, but no increase in radiolabel incorporation was apparent for any sample when compared to controls. The temporal relation between the radioiodine and the acute onset of dermopathy and ophthalmopathy, together with the abrupt rise in TRAbs, indicates a probable causal association. However, the absence of in-vitro fibroblast stimulation would suggest that the pathogenesis of Graves' dermopathy is not dependent solely on any simple humoral factor.

Autoantibodies↗
PubMed1995

Rectification of whole cell cystic fibrosis transmembrane conductance regulator chloride current.

Whole cell epithelial cystic fibrosis transmembrane conductance regulator (CFTR) Cl- currents exhibited a linear current-voltage (I-V) relationship with high symmetrical transmembrane Cl- concentrations. However, when intracellular Cl- (Cli-) was reduced by replacement with glutamate, I-V relationships were outwardly rectifying. Rectification was not affected by reducing extracellular Cl- to eliminate or reverse the gradient, indicating that rectification is not a function of the Cl- gradient. Rectification was affected by Cli- in a concentration-dependent manner, and it was weaker when Cli- was reduced by replacement with sucrose. These characteristics are identical to those of the cardiac isoform of CFTR, and the experimental data could be simulated by an Eyring rate theory model assuming that permeating anions interact at a single binding site within the channel pore. No evidence was found for multiple binding sites. These results indicate that rectification is a function of the concentration and permeability of the anions inside the cell. It is concluded that rectification of CFTR Cl- current is a property of ion channel permeation that would occur under physiological conditions and that permeation of the epithelial and cardiac isoforms of CFTR is identical.

1-Methyl-3-isobutylxanthine↗