Voltage dependence of acetylcholine-activated membrane conductance in sympathetic ganglion neurons

Acetylcholine-induced membrane conductance was investigated in superior cervical ganglion neurons using a patch-clamp technique. It was found that hyperpolarization and depolarization produce an increase and a reduction in acetylcholine (ACh) conductance. This reduction was unconnected with either reversal of the current induced by iontophoretic ACh application or the presence of Ca ions in the external solution. The time constant of relaxation (_r) of this current, produced by a jump in membrane potential, was found to increase e-fold when the membrane was hyperpolarized by 70 mV, matching the voltage dependence of ACh conductance. This led to the hypothesis that voltage-dependent ACh-induced conductance is entirely determined by the voltage dependence of nicotinic receptor channel gating kinetics.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 2, pp. 167–171, March–April, 1988.     

Effect of Lincocin Treatment on the Greening Process in Bean (Phaseolus vulgaris) Leaves

The effect of lincocin (a plastid protein synthesis inhibitor) treatment on the greening process of bean (Phaseolus vulgaris L.) leaves have been studied. In comparison with control leaves treated ones had a decreased rate of chloroplast development. They had a marked chlorophyll deficiency and a decreased chlorophyll a/b ratio. Some long and short wavelength forms of chlorophyll a were lacking as evidenced from the absorption spectra at 25°C and the fluorescence spectra at 77°K. The –¹⁴CO₂ fixation was inhibited by 80–90% in treated leaves. The fluorescence induced by the measuring light was greater in the treated leaves than in the control ones, and the kinetics of the decline of the relative fluorescence intensity were also different. Electron microscopic studies showed macrogranum-like structures and incomplete membrane vesicles in the treated plastids. After longer treatment a destruction of membranes was observed. The results indicate some structural and functional membrane deficiencies and instability of the membranes.     

Lecithotrophic development and metamorphosis in the Indo-West Pacific brittle star Ophiomastix venosa (Echinodermata: Ophiuroidea)

Summary

The larval development of the ophiocomid ophiuroid Ophiomastix venosais described using SEM. The gastrula transforms into a uniformly ciliated early larva which progressively changes into a lecithotrophic late premetamorphic larva with a continuous bilateral ciliated band. This stage is short-lived and equivalent to a highly reduced ophiopluteus. Comparisons between O. venosa and other ophiuroid species whose development has been investigated suggest that, whatever the developmental mode (lecithotrophic or planktotrophic), a pluteus stage always occurs in ophiuroids with planktonic development. Two metamorphic stages were identified, the late metamorphic larva differing from the early one by the closure of the larval mouth. The appearance of the permanent mouth marks the end of the metamorphosis. The postlarva still possesses remnants of larval features. The transformation of the reduced ophiopluteus into a barrel-shaped metamorphic larva with transverse ciliated bands, a vitellaria larva, is followed. The possible occurrence of a unique type of metamorphic larva in non-brooding ophiuroids is discussed. Verification of this, however, needs further SEM investigations on metamorphic larva from species having “regular” planktotrophic development.     

Functional activity of adenylyl and guanylyl cyclases in human spermatozoa with different motility

The most important functional characteristic of ejaculated spermatozoa is their ability to engage in directed sustained movement, which to a large extent determines their fertility. It is assumed that enzymes with cyclase activity—adenylyl cyclase (AC) and guanylyl cyclase (GC)—soluble and membrane-bound forms of which are found in human and mammalian sperm, play the key role in regulation of motility. However, the functional activity of the cyclases in ejaculated spermatozoa with different motilities and their contribution to the regulation of this process are virtually unexplored. The goal of this work was to determine the functional characteristics of AC and GC in ejaculates of human spermatozoa with different contents of motile forms and the study of regulation of these enzymes by hormones and nonhormonal agents. We found differences in the activity and regulatory properties of AC and GC in ejaculates differing in motile forms of spermatozoa. The basal AC activity and its sensitivity to bicarbonate anions and manganese cations, activators of cytosolic AC (cAC), were increased in ejaculates with a high proportion of motile spermatozoa. At the same time, the AC effects of forskolin, GppNHp, and adrenergic receptor agonists acting via membrane-bound AC (mAC) in this case were significantly reduced. Cytosolic GC in the ejaculates with a high proportion of motile spermatozoa was more sensitive to manganese cations, but the basal activity of GC was altered slightly. An increase in the content of motile spermatozoa in ejaculate led to a decrease in the sensitivity of CNP to receptor GC, while the sensitivity to ANP was maintained, which indicates a change in the pattern of enzyme regulation with natriuretic peptides in favor of ANP, an important regulator of sperm chemotaxis. Thus, we have concluded that the change in proportion of motile spermatozoa in ejaculate induces changes of functional activity and regulatory properties of soluble and membrane-bound forms of AC and GC, which can be used to control the motility, chemotaxis, acrosomal reaction, and other processes determining fertility of male germ cells.     

The effect of prolonged intranasal administration of serotonin on the activity of hypothalamic signaling systems in male rats with neonatal diabetes

The functioning of the serotonergic system of the brain is impaired in type II diabetes (T2D), and this leads to metabolic and hormonal dysfunction. The elevation of serotonin level in the CNS is one of the approaches for correcting of the serotonergic system of the brain. The aim of the present work was to investigate the effect of intranasal serotonin (InS) administration for 5 weeks at a daily dose of 20 μg on the metabolic parameters and functional activity of adenylate cyclase signaling system (ACSS) sensitive to peptide hormones and biogenic amines in the hypothalamus of male rats with neonatal T2D. Neonatal model of T2D was induced by injecting streptozotocin (70 mg/kg) into 5-day-old rat pups. Four-month-old animals with apparent T2D manifestations were divided into two groups: an untreated group (D0, n = 6) and a group that received InS treatment (DIS, n = 6). InS administration to diabetic rats restored ACSS regulation by the agonists of type 2 dopamine receptors (DA₂R) and type 4 melanocortin receptors (MC₄R) and enhanced the inhibitory effect of serotonin on adenylate cyclase activity. Elevated expression of genes encoding DA₂R, MC₄R, and serotonin receptor of the 1B subtype (5-HT_1BR) was among the main causes of this change. The relative activity of signaling cascades involving various types of serotonin (G_s-coupled 5-HT_4,6,7R/G_i-coupled 5-HT₁R), dopamine (DA₁R/ DA₂R), and melanocortin (MC₃R/MC₄R) receptors involved in ACSS regulation was also altered in the animals of the DIS group. InS administration restored hormonal regulation in the hypothalamus, improved glucose tolerance, and increased the sensitivity of tissues to insulin. The data obtained show that the elevation of serotonin level in the CNS is a promising approach for the recovery of hypothalamic signaling pathways in T2D and correction of the metabolic disturbances dependent on these pathways.     

High dimensional mediation analysis with latent variables

We propose a model for high dimensional mediation analysis that includes latent variables. We describe our model in the context of an epidemiologic study for incident breast cancer with one exposure and a large number of biomarkers (i.e., potential mediators). We assume that the exposure directly influences a group of latent, or unmeasured, factors which are associated with both the outcome and a subset of the biomarkers. The biomarkers associated with the latent factors linking the exposure to the outcome are considered “mediators.” We derive the likelihood for this model and develop an expectation‐maximization algorithm to maximize an L1‐penalized version of this likelihood to limit the number of factors and associated biomarkers. We show that the resulting estimates are consistent and that the estimates of the nonzero parameters have an asymptotically normal distribution. In simulations, procedures based on this new model can have significantly higher power for detecting the mediating biomarkers compared with the simpler approaches. We apply our method to a study that evaluates the relationship between body mass index, 481 metabolic measurements, and estrogen‐receptor positive breast cancer.     

The hormone-sensitive adenylyl cyclase system of the ciliate Dileptus anser

The hormone-sensitive adenylyl cyclase system (AC system) was found and characterized for unicellular eukaryotes--the ciliatae Dileptus anser. It has been first shown that hormones of higher eukaryotes--biogenic amines (adrenalin, isoproterenol and serotonin) and peptide glucagon--stimulate in dose-dependent manner the activity of adenylyl cyclase (AC) of D. anser. The enzymatic activity was stimulated also by guanine nucleotides--GTP and their non-hydrolysable analogue Gpp[NH]p. Stimulating effects of hormones and guanine nucleotides strongly depend on the level of AC basal activity, which is relatively easy to reach (1430 to 3900 pmol cAMP/min per 1 mg of protein). The sensitivity of D. anser AC system to hormones and guanine nucleotides shows the presence of receptor or receptor-related molecules, capable of interacting with the hormone and activating AC through heterotrimeric G-proteins, in ciliatae. On the base of obtained data, a conclusion is made about the similarity of the structural-functional organization of AC systems of D. anser and higher eukaryotes.     

Peptides derived from the third cytoplasmatic loop of serotonin 1B receptor subtype selectively inhibit serotonin signal transduction via a homologous receptor

The third intracellular loops of hormonal receptors play the main role in the interaction of majority of the serpentine type receptors with heterotrimeric G-proteins. In recent years, it was shown that synthetic peptides corresponding to membrane-proximal regions of these loops could be selectively influenced with hormonal signal transduction via the receptors homologous to them and trigger signalling cascade in absence of the hormone. For the first time, we succeeded in synthesizing the peptides derived from C-terminal region of the third intracellular loop of the IB-subtype serotonin receptor and studied their influence on serotonin-sensitive adenylyl cyclase system in the rat brain. The peptides 300-316 and 306-316 (the numbers correspond to amino acid positions in the rat IB-subtype serotonin receptor) at micromolar concentrations in absence of hormone-stimulated GTP-binding of Gi,-proteins coupled with the IB-subtype serotonin receptors and inhibited forskolin-stimulated adenylyl cyclase activity. Using selective agonists and antagonists of serotonin receptors it was shown that the peptides 300-316 and 306--316 inhibited serotonin signal transduction via homologous to them receptor and weakly influenced other types of serotonin receptors. The peptide 300-316 is more active compared with its shorter analogue 306-316 in the selectivity and efficiency of action on adenylyl cyclase signalling system regulated via the IB-subtype serotonin receptors. These findings indicate that the regions 300-316 of the IB-subtype serotonin receptor are involved in interaction with Grproteins and consist of the main molecular determinants responsible for serotonin signal transduction to adenylyl cyclase.