Internal dialysis of Limulus ventral photoreceptors

The internal dialysis technique has been applied to Limulus ventral photoreceptors. This method potentially allows quantitative control of the concentration of diffusible molecules within living cells. During dialysis, Limulus photoreceptors retained their ability to respond to light. Under conditions of dim illumination, responses were normal for close to an hour. In bright light, abnormalities developed more rapidly. The reversible effects of raising the dialysate Mg2+ concentration and the entrance of rhodamine-labeled albumin into cells shows that the dialysis method is useful for assaying the effects of small or large molecules on visual transduction. This method has been used to examine the effects of nucleotide triphosphates and cyclic nucleotides. The results show that nucleotide triphosphates (5-10 mM) are required to maintain a low rate of spontaneous quantum bumps. The importance of cyclic nucleotides in transduction is less clear; the light response was reduced by either cGMP or cAMP but only at very high concentrations (10 mM).

The action of peptides and cyclic nucleotides on the nervous system of an insect

Eclosion hormone (EH) is a moderate-sized peptide that acts on the insect nervous system to release the stereotyped behaviors involved in shedding the old skin (eclosion) as well as to activate new reflex pathways. The action of the peptide has been studied by using two preparations. The first preparation involves the preeclosion and eclosion motor programs that can be released from the isolated abdominal central nervous system (CNS) in response to EH. The target sites associated with the release of these programs are scattered throughout the CNS, each apparently being associated with a segmental component of one of the programs. A fully coordinated behavioral response requires that all these segmental elements be exposed to the peptide. The second preparation has allowed the cellular analysis of a simple multisegmental reflex that is turned on by EH. The data indicate that the reflex pathway is activated by the peptide through the selective action on a key synaptic junction. In the case of both of these preparations, the action of EH appears to involve an increase in cyclic GMP levels in the CNS. The manner by which these increases result in altered neuronal activity remains unknown.

The role of prostaglandins, cyclic nucleotides and tricarboxylic acids in the regulation of the human placental 20 alpha-hydroxysteroid dehydrogenase in vitro

The in vitro effect of non-steroidal regulators (prostaglandins, cyclic nucleotides and tricarboxylic acids) on the cytoplasmic 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSDH, EC 1.1.1.149) isolated from human early gestational and term placentas was investigated. When prostaglandins (PG) were tested at 100 microM concentrations, an inhibition of the human placental 20 alpha-HSDH by PGE1 (80% inhibition), PGE2 (70%), PGF1 alpha (40%) PGF2 alpha (30%) and 13,14-dihydro-15-keto-PGF2 (PGFM) (20%) was observed. This effect was shown to be dose-dependent. The I50 (concentration at 50% inhibition) was determined for PGE1 and PGE2 to be 11 microM and 38 microM, respectively. No effect on the activity of the 20 alpha-HSDH could be demonstrated for PGI2 and its stable metabolite 6-keto-PGF1 alpha, for the cyclic nucleotides (dbcAMP, dbcGMP) and for the tricarboxylic acids (citrate, ketoglutarate, lactate, malonate, pyruvate and succinate) when added to the incubation at 100 microM concentration. The 20 alpha-HSDH isolated from early gestational and term placentas did not respond differently to the substances tested. These results suggest that prostaglandins can have a direct, dose-dependent effect on the isolated human placental 20 alpha-HSDH without cyclic nucleotides as intermediates and thereby play a role in the regulation of human progesterone synthesis and metabolism during pregnancy and near term.

Roles of cyclic nucleotides in the synaptic transmission in sympathetic ganglia of rabbits

1. Two kinds of slow postsynaptic potentials can be elicitable in the rabbit superior cervical ganglion: a dopaminergic hyperpolarizing (slow IPSP) one and a muscarinic depolarizing (slow EPSP) one, respectively. 2. Cyclic AMP may not be involved in the generation of slow IPSP, whereas it certainly mediates the dopamine-induced enduring modulatory enhancement of the slow EPSP response. 3. Cyclic GMP appears to mediate at least one of the components in the mechanism underlying the slow EPSP by generating a depolarization with no change in membrane conductance. 4. Cyclic GMP does additionally regulate the dopamine for cyclic AMP)-induced modulatory enhancement of the slow EPSP by antagonizing it in a uniquely time-dependent fashion.

The stimulation of inositol lipid metabolism that accompanies calcium mobilization in stimulated cells: defined characteristics and unanswered questions

It now appears to be generally agreed that the 'phosphatidylinositol response', discovered in 1953 by Hokin & Hokin, occurs universally when cells are stimulated by ligands that cause an elevation of the ionized calcium concentration of the cytosol. The initiating reaction is almost certainly hydrolysis of an inositol lipid by a phosphodiesterase. Phosphatidylinositol, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate all break down rapidly under such circumstances. However, we do not yet know which of these individual reactions is most closely coupled to receptor stimulation, nor do we know where in the cell it occurs. With many stimuli, inositol phospholipid breakdown is closely coupled to occupation of receptors and appears not to be a response to changes in cytosol [Ca2+]: this provoked the suggestion that it may be a reaction essential to the coupling between activation of receptors and the mobilization of Ca2+ within the cell. In a few situations, however, it appears probable that inositol lipid breakdown can occur as a result of the rise in cytosol [Ca2+] that follows receptor activation: such observations gave rise to the alternative opinion that inositol lipid breakdown cannot be related to stimulus-response coupling at calcium-mobilizing receptors. It now seems likely that these two views are too rigidly polarized and that some cells probably display both receptor-linked and Ca2+-controlled breakdown of inositol lipids. Both may sometimes occur simultaneously or sequentially in the same cell.

Regulation of pancreatic exocrine secretion in vitro: the action of secretagogues

Pancreatic acinar cells possess two functionally distinct mechanisms by which secretagogues can increase enzyme secretion. One mechanism is mediated by mobilization of cellular calcium and can be activated by any one of four different classes of receptors. The other mechanism is mediated by cyclic AMP and can be activated by either of two different classes of receptors. In addition to stimulating enzyme secretion, a secretagogue can cause potentiation of secretion, desensitization to the subsequent stimulation caused by the same or other secretagogues as well as residual stimulation of enzyme secretion. Although each class of secretagogue receptors can cause the same final effect, stimulation of enzyme secretion, the existence of multiple classes of receptors and the different mechanisms of action endow the acinar cell with a wide range of patterns of response depending on which of the several classes of receptors are activated.

Analgesia following microinjection of phosphodiesterase inhibitors at brainstem sites

Microinjection of RO 20-1724 (0.60 micrograms) at sites in the caudal reticular formation of the rat brainstem resulted in analgesia as measured in the tail flick, paw pinch and hot plate tests. Microinjection of theophylline (0.45 micrograms) at sites in the caudal reticular formation also produced analgesia in the tail flick and hot plate tests, but not in the paw pinch test. Since these agents inhibit phosphodiesterase and elevate cyclic nucleotides in rat brain homogenates, these data suggest that cyclic nucleotides have a functional role in brainstem structures involved in modulation of nociceptive threshold.

Molecular and cellular mechanisms of leukocyte chemotaxis

The application of modern scientific methods to the study of leukocyte function has begun to reveal the molecular and cytostructural bases of the chemotactic responses of these cells. Leukocyte chemotaxis is initiated by the binding of chemoattractants to distinct plasma membrane receptors; this finding alters transmembrane potential and activates ionic fluxes. The subsequent sequence of metabolic processes leads to a rearrangement of cytoskeletal elements that is manifested by orientation and migration of the cells toward the source of the chemotactic gradient.

Lung catecholamines and cyclic nucleotides during perinatal development in the rat. Possible relationships with biochemical and morphological differentiation

In this study, we investigated in parallel the evolution of endogenous catecholamine and cyclic nucleotide levels in lung tissue in the course of normal fetal development of the rat from day 17 of gestation to day 10 postpartum; the findings were correlated with the successive stages of lung differentiation. These were assessed morphologically by electron microscopy, and biochemically by measuring the levels of the main lung tissue phospholipids and studying their fatty acid composition. Dopamine levels were low and always remained under 5 ng/g of wet tissue. Nevertheless, slight rises were observed between days 17 and 19 of gestation (1.8 and 2.78 ng/g, respectively) and between days 21 of gestation and birth (2.56 and 4.25 ng/g, respectively). These changes were significant (P less than 0.05). Norepinephrine (NE) levels first decreased by about 50% between days 17 and 19 of gestation (7.34 and 3.88 ng/g, respectively), (P less than 0.01) and then rose sharply about 4 times until birth (17.24 +/- 3.90 ng/g), and more slowly from then on. On day 10 postpartum, the mean NE level was 34.31 +/- 3.28 ng/g. The levels of the two cyclic nucleotides [cyclic adenosine 3':5'-monophosphate and cyclic guanosine 5'-monophosphate (cGMP)] were quite high on day 17 and remained so until day 19 (cAMP = 220 pmoles /g; cGMP = 20 pmoles/g). From day 19 until day 21, the levels of the two nucleotides decreased (cAMP = 140 pmoles/g; cGMP = 8 pmoles/g; P less than 0.05). During this period, the decrease in cGMP level was about twice that of cAMP. During the last day of gestation, the cAMP level was still decreasing, whereas cGMP was increasing. After birth, the levels of the two cyclic nucleotides rapidly increased to day 5. Between days 5 and 10 postpartum, no significant changes were observed in either cAMP or cGMP levels. The time course of the variations reported suggests that they are related to the maturation processes of lung assessed on the basis of morphological and biochemical criteria. On day 19 of gestation, when the first lamellar bodies appear, large changes occur in the evolution of NE and cyclic nucleotide levels, suggesting that these changes may be related to the onset of surfactant synthesis. On day 21 of gestation, the cAMP and cGMP ratio rises sharply; at the same time, the total phospholipid level is increased by 50%. At this stage, lamellar bodies are actively differentiating within type II pneumocytes and massively released into the fetal airways. The relationships between the variations of the studied biochemical parameters and the maturation processes of lung suggest that dopamine and NE could be involved in surfactant synthesis and release via their second messenger, the cyclic nucleotides. Further investigations are needed to elucidate the mechanisms regulating these changes.

Sympathetic innervation of murine thymus and spleen: a comparative histofluorescence study

Fluorescence microscopy of thymus and spleen from four strains of mice (C3H and ICR controls, AKR spontaneously leukemic and NZB autoimmune) revealed varicose noradrenergic (NE) fibers in perivascular and parenchymal regions of both organs. Thymic innervation was largely perivascular, but isolated islands and strings of free NE fibers were noted among thymic parenchymal cells. A morphological proximity between NE fibers in the thymus and mast cells was noted in all strains studied, but was exceptionally prominent in the NZB thymus. Perivascular plexuses within the splenic white pulp sent single NE fibers between the surrounding lymphocytes. Catecholamines and histamine have been shown to modulate lymphocyte development and activity in vitro. The present study provides morphological evidence that both NE and histamine are available to lymphocytes in thymus and spleen, and thus provides morphological evidence for neural modulation of immune activity in vivo.