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Biomedical subjects

K P Minneman

Publications and source records attributed to K P Minneman.

At least 19 recordsLinked to original sources
PubMed1992

Subtypes of alpha 1-adrenoceptors in DDT1 MF-2 and BC3H-1 clonal cell lines.

We examined which subtype(s) of alpha 1-adrenoceptors are expressed in the widely used DDT1 MF-2 and BC3H-1 cell lines. Pretreatment with chloroethylclonidine (CEC) inactivated 76-85% of the specific [125I]BE 2254 binding sites in membrane preparations from both cell lines. Competition with subtype-selective competitive antagonists showed primarily the alpha 1B subtype in both cell lines. However, in BC3H-1 cells 5-methyl-urapidil showed complex behavior suggesting that about half of the binding sites had a lower affinity. Chloroethylclonidine pretreatment eliminated [3H]inositol phosphate responses to norepinephrine in both cell lines. Measurement of intracellular Ca2+ with fura-2 in DDT1 MF-2 cells showed that norepinephrine induced a complex response involving both transient and sustained components. Chloroethylclonidine pretreatment blocked both responses, while chelation of extracellular Ca2+ left the transient response intact but eliminated the sustained component. These results support previous work that these cell lines contain alpha 1B-adrenoceptors linked to inositol phosphate formation and mobilization of intracellular Ca2+. However, these results show that alpha 1B-adrenoceptors can be linked to Ca2+ influx as well as intracellular mobilization, and support the existence of pharmacologically distinct alpha 1B variants.

Adrenergic alpha-Antagonists↗
PubMed1992

Preferential desensitization of beta- versus alpha 2-adrenergic receptors accelerates loss of response to norepinephrine in primary glial cultures.

The effect of norepinephrine (NE) on cAMP accumulation in primary glial cultures is mediated by two functionally opposing receptor subtypes. beta-Adrenergic receptor activation increases cAMP formation, whereas simultaneous alpha 2-adrenergic receptor activation partially inhibits this effect. We compared desensitization of these two responses during exposure to selective agonists or NE. Pretreatment with the beta-selective agonist isoproterenol (ISO) decreased responses to ISO, ISO plus the alpha 2-selective agonist UK 14,304 (UK), and NE. However, ISO plus UK and NE responses decreased more, relative to their control values, than did responses to ISO alone. Pretreatment with UK increased cAMP responses to both ISO and forskolin (sensitization), with little effect on alpha 2-mediated inhibition of these responses. Pretreatment with NE caused effects similar to those of both ISO and UK pretreatment. NE pretreatment decreased responses to ISO, ISO plus UK, and NE, sensitized responses to forskolin, and had little effect on alpha 2-mediated inhibition. Thus, chronic agonist exposure desensitizes beta-adrenergic receptors more rapidly and at much lower concentrations than alpha 2-adrenergic receptors in these cultures. The continuing alpha 2 inhibition during diminishing beta stimulation functionally accelerates the loss of the NE response.

Adrenergic alpha-Agonists↗
PubMed1992

Coexisting beta 1- and atypical beta-adrenergic receptors cause redundant increases in cyclic AMP in human neuroblastoma cells.

In SK-N-MC human neuroblastoma cells, the cAMP response to 10 nM isoproterenol (ISO) is mediated primarily by beta 1-adrenergic receptors. However, responses to higher concentrations of ISO (100-1000 nM) were only weakly blocked by beta 1- and beta 2-selective antagonists. When beta 1 receptors were blocked with 10 microM CGP 20712A, catecholamines still maximally activated cAMP accumulation, with only small decreases in potency. In the presence of CGP 20712A, beta blockers inhibited the response to ISO stereoselectively but with relatively low potencies. Pindolol derivatives were partial agonists with low potencies, and the atypical agonist BRL 37344 was a partial agonist with an intermediate potency. All binding sites in these cells labeled by 125I-cyanopindolol were of the beta 1 subtype. Nuclease protection assays indicated that SK-N-MC cells contain mRNA for both the human beta 1- and beta 3-adrenergic receptors, with the beta 3 subtype mRNA being expressed 25-50% more abundantly than that for the beta 1 subtype. Northern blot hybridizations showed the presence of two beta 3 mRNA transcripts of 3.1 and 2.4 kilobases. These results suggest that beta 1- and atypical beta-adrenergic receptors coexist in these cells and cause redundant increases in cAMP formation. Although molecular approaches suggest that the atypical subtype is the beta 3, the observed drug specificity differs from that reported for the expressed recombinant human beta 3 receptor.

Adrenergic beta-Agonists↗
PubMed1992

Occupancy-response relationships for beta- and alpha 2-adrenergic receptors exerting opposing effects on cAMP production.

In primary glial cultures, norepinephrine (NE) activates both beta-adrenergic receptors to increase cAMP formation and alpha 2-adrenergic receptors to partially inhibit this response. We used selective alkylating agents to compare the concentration-dependence and receptor reserves for activation of each subtype. Partial inactivation of beta-receptors with alkylating pindolol (BIM) caused a slight decrease in the potency of isoproterenol (ISO) in increasing cAMP accumulation and a progressive decrease in maximum response. The KA for ISO was 9.8 +/- 2 nM, with a 2-3-fold beta-receptor reserve. BIM pretreatment decreased the maximal response to NE without significantly altering its apparent EC50 (41 +/- 6.7 nM). Partial inactivation of alpha 2-adrenergic receptors with EEDQ increased the maximal response to NE without significantly altering its apparent EC50 (41 +/- 6.2 nM). NE inhibited the cAMP response to ISO with an apparent EC50 of 38 +/- 1.2 nM. EEDQ pretreatment reduced inhibition of the ISO response by both NE and the alpha 2-agonist UK 14,304, and inhibition of the forskolin response by UK 14,304. EEDQ pretreatment caused only a small decrease in potency for the alpha 2-agonists. The KA for NE in inhibiting the ISO response was 120 +/- 30 nM, indicating a 2-3-fold alpha 2-receptor reserve. These results suggest that NE has similar affinities and receptor reserves for beta- and alpha 2-adrenergic receptors in this system, and activates and inhibits adenylate cyclase at the same agonist concentrations.

Adrenergic alpha-Antagonists↗
PubMed1979

Fundamental difference between the molecular interactions of agonists and antagonists with the beta-adrenergic receptor.

Antagonist binding to the beta-adrenergic receptor is largely entropy driven, with only a small enthalpy component. The binding of agonists, on the other hand, is associated with a large decrease in enthalpy which permits a highly unfavourable decrease in entropy. The thermodynamic differences between the binding of agonists and antagonists may provide new insights into the molecular basis for hormone stimulation of adenylate cyclase activity.

Adenylyl Cyclases↗
PubMed1979

beta1- and beta2-Adrenergic receptors in rat cerebral cortex are independently regulated.

Repeated administration of the tricyclic antidepressant desmethylimipramine to adult rats for 10 days caused a 40% decrease in the density of beta1-adrenergic receptors in the cerebral cortex but had no effect on the density of beta2-adrenergic receptors. Conversely, destruction of noradrenergic neurons by administration of 6-hydroxydopamine to neonatal rats caused a 64% increase in the density of beta1-adrenergic receptors in adult cerebral cortex with no change in the density of beta2-adrenergic receptors. These results suggest that the beta-adrenergic receptors in rat cortex involved in neuronal function are primarily of the beta1 subtype.

Adrenergic beta-Agonists↗
PubMed1978

Receptor-linked cyclic AMP systems in rat neostriatum: differential localization revealed by kainic acid injection.

Various receptor-linked cyclic AMP systems were measured in rat neostriatum 2--14 days after selective destruction of neuronal cell bodies and dendrites by micro-injection of 3 microgram of kainic acid. Basal adenylate cyclase activity was reduced by up to 56% in the injected side and the sensitivity to dopamine was abolished. Up to 84% of cyclic nucleotide phosphodiesterase activity, hydrolyzing either cyclic AMP or cyclic GMP, was destroyed by kainic acid injection. Specific binding of [3H]etorphine and [3H]spiroperidol was reduced by up to 62% in the injected side, while non-specific binding was unchanged. All of these changes were time-dependent, and were greatest 7--14 days after kainic acid treatment. On the other hand, intrastriatal kainic acid injection caused no change in the steady-state concentration of cyclic AMP in striatal slices, or in the in vivo cyclic AMP content in the striatum of rats killed by microwave irradiation. Receptor-mediated increases in cyclic AMP accumulation in striatal slices were either unchanged or markedly potentiated by kainic acid treatment. The maximum response to adenosine was unchanged, while the response to isoprenaline was increased up to 3.7-fold, the response to dopamine increased up to 6.7-fold, and the response to PGE1 increased up to 30-fold. The effect of dopamine in kainic acid-treated striatal slices was no longer blocked by fluphenazine, but was blocked by propranolol, suggesting an interaction of dopamine with a beta-adrenoceptor in kainic acid-treated slices. The results suggest differential cellular localizations of the various receptor-linked cyclic AMP systems in rat neostriatum. Some dopamine and opiate receptors, as well as most of the phosphodiesterase activity, are associated with local neuronal elements, while beta-adrenoceptor, adenosine and PGE1 alterations in cyclic AMP are not. The potentiation of the beta-adrenoceptor and PGE1 responses suggests that they may occur in glial cells. In addition, the pool of adenylate cyclase destroyed by kainic acid appears to make little contribution to normal levels of cyclic AMP in the tissue.

3',5'-Cyclic-AMP Phosphodiesterases↗