E. Daniele

Biochemical and functional evidence for the presence of dopamine D1 receptors in the bovine ciliary body

The present paper reports both functional and biochemical evidence for the presence of dopamine D1 receptors in the bovine ciliary body. Dopamine (DA) and dopamine D1 agonists (such as SKF 38,393) but not D2 agonists (such as LY 141,865) produced a concentration-related decrease in the tone induced by a maximally active concentration of carbachol (1 x 10(-4)-5 x 10(-4) M). The maximal relaxation obtained was 100% of the carbachol response using 10(-5) M dopamine or 5 x 10(-6) M SKF 38,393. SCH 23,390, a D1 antagonist, but not (-)-sulpiride, antagonized the effect of DA and SKF 38,393. In accordance with the functional data, radioreceptor binding experiments revealed the existence of a high affinity saturable [3H]SCH 23,390 binding to membranes prepared from ciliary body (Bmax: 344 fmol mg protein-1; Kd: 0.87 nM). The binding was specifically displaced by SCH 23,390, dopamine and dopamine D1 agonists, but not by norepinephrine, D2 agonists, or antagonists such as LY 141,865 and sulpiride. No specific binding was found when using dopamine D2 ligands, such as tritiated spiroperidol.

Substance p as a transmitter in the human ciliary muscle

The present experiments, carried out on the human fresh ciliary muscle, were undertaken to define whether substance P is involved as an excitatory transmitter in the contractile response evoked by electrical stimulation. Our results show that, following cholinergic and adrenergic blockade, the resistant component of contraction was completely abolished by (D-Pro2-D-Trp7,9)-SP, a synthetic analogue of substance P with antagonistic activity. Moreover the effects of exogenous substance P were investigated.

Evidence for protein kinase C modulation of the ciliary muscle response to carbachol and desensitization

The role of protein kinase C (PKC) in the desensitization of muscarinic receptor-mediated responses in bovine ciliary muscle was examined. Exposure of the bovine ciliary muscle to phorbol esters, used to activate PKC, resulted in antagonism of muscarinic receptor-mediated contraction. On the other hand, staurosporine, a known PKC inhibitor, caused a significant potentiation of the contractile effect induced by carbachol. Staurosporine reduced the desensitization induced by repeated additions of carbachol and completely suppressed that induced by phorbol esters. The results also indicate that desensitization mediated by phorbol esters as well as that mediated by muscarinic receptor agonists is heterologous.

Effects of phorbol ester on carbachol-induced contraction in bovine ciliary muscle: possible involvement of protein kinase C

The aim of the research was to characterize muscarinic receptors of bovine ciliary muscle and to investigate the desensitization process. The role of protein kinase C was analyzed. The results show that muscarinic receptors of bovine ciliary muscle have the pharmacological characteristics of the M3 subtype. Acute exposure to phorbol esters (1 microM phorbol 12,13-dibutyrate, PDB, or 0.1 microM phorbol 12-myristate 13-acetate, PMA, for 15 and 5 min, respectively) resulted in antagonism of muscarinic receptor-mediated contraction. Long-term pretreatment (18 h) with PMA to down-regulate protein kinase C resulted in potentiation of carbachol-induced contraction, reduction of agonist-induced desensitization and loss of phorbol ester-induced desensitization. Staurosporine (3 microM) and H7 [1-(5-isoquinolinesulfonyl)-2-methyl-piperazine] (1 microM), protein kinase C inhibitors, produced a significant potentiation of the contractile effect of carbachol, reduced the desensitization produced by repeated addition of carbachol and suppressed that induced by phorbol esters. In vitro incubation with carbachol, PDB or PMA did not cause any modification of the binding of labeled [3H]quinuclidinyl benzilate. In vitro incubation with PDB and PMA produced, as expected, a significant translocation of protein kinase C from the cytosol to the membrane. The incubation of the ciliary muscle with carbachol, using the protocol of exposure that induced maximal desensitization of contractile responses, produced a significant redistribution of the enzyme from the cytosol to the membrane. These findings suggest that agonist-induced modulation of functional cholinergic sensitivity in ciliary muscle is correlated, at least partially, to the translocation of protein kinase C from the cytosol to the membrane. The desensitization by phorbol esters is completely due to protein kinase C activation; during the desensitization process, direct modification of the density and affinity of muscarinic receptors is not involved.

Synthesis and dopamine receptor affinities of 1-aminoethylhetero-tetralines

Abstract A series of 1-aminoethylhetero-tetralines 3–6 , which can be considered as opened-structure analogues of previously studied dopaminergic compounds 2 , were synthesized. In the binding studies, to evaluate D-1 and D-2 activity, no significant affinity was observed towards both dopaminergic receptors.

Neurochemical changes produced by perinatal exposure to lead

Lead poisoning has been a medically recognized entity since ancient times. This fact and the wide industrial use of this metal have generated an enormous number of studies on the toxic effects of lead and on the underlying mechanisms of toxicity.

The effect of thymoxamine on guinea-pig ileum contractions.

The effects of thymoxamine on the contractions induced in guinea-pig isolated ileum were examined. The drug was tested in a large range of concentrations (10(-8)-10(-4) M). The twitch response induced by acetylcholine was potentiated by low concentrations and inhibited by high concentrations of the alpha 1-blocking drug thymoxamine. The contractions in response to carbachol were always inhibited. Thymoxamine also affected the responses of the ileum to other stimulants: angiotensin, pentagastrin, cholecystokinin. The drug (8 X 10(-5), 5 X 10(-4) M) inhibited the calcium contraction of high K+ depolarized preparations.