The effects of ryanodine,acetylcholine and epinephrine on electrical and mechanical activity in an insect heart

• 1.1. Ryanodine, an alkaloid used as an insecticide, has been shown to depress contraction while leaving excitation unaffected in mammalian hearts, an effect presumed to result from uncoupling of the transverse tubular system (TTS) from the sarcoplasmic reticulum (SR).
• 2.2. The heart of the adult moth Hyalophora cecropia, a tissue known to have septate junctions between the TTS and SR and a Ca²⁺ -spike generating sarcolemma was used to further test this hypothesis.
• 3.3. We first report the basic characteristics of the contractile response and demonstrate a negative force-frequency effect, a diminished calcium current (I_Ca²⁺) in the presence of acetylcholine and an enhanced I_Ca²⁺ with epinephrine.
• 4.4. Ryanodine 10⁻⁸M added to this preparation slowed the inherent rhythm (interval 0.6–4 sec), depolarized the cells by 10–14 mV, reduced action-potential amplitude (from 66 to 52 mV), prolonged the plateau (from 80 to 280 msec), and decreased dV/dt from 4 to 2.8 V/sec.
• 5.5. The magnitude of peak tension was not affected, but the time to peak tension was increased from 160 to 200 msec and the relaxation time was prolonged from 200 to 480 msec.
• 6.6. The refractory period was increased, thereby preventing the heart from following increased rates of pacing by externally applied stimuli.
• 7.7. We conclude that ryanodine interferes first with the sarcolemmal Ca²⁺-delivery system and then the SR calcium-sequestration system.

     

Functional differentiation of crayfish statocyst receptors in sensory adaptation

• 1.1. Response characteristics of tonic- and phasic-type receptors in the crayfish statocyst were investigated with intracellular recording technique.
• 2.2. They were identified to be either tonic- or phasic-type according to their response patterns to the hair deflection performed by water jet stimulation.
• 3.3. Constant depolarizing current applied intracellularly evoked long-lasting spike discharge in the tonic-type neurons and transient discharge in the phasic-type neurons.
• 4.4. These tonic- and phasic-type neurons also showed different patterns of spike discharge to depolarizing pulse stimulus of 50 msec duration.
• 5.5. On the basis of the response patterns to this pulse stimulus, it was shown that the statocyst receptor neurons consist of 46% tonic- and 54% phasic-type neurons.

     

Evidence for the presence of ion pumps in the photophores of two mesopelagic fishes: Argyropelecus and maurolicus

• 1.l. Adenosine triphosphatase (ATPase) activity has been measured on homogenates of photophores from the two mesopelagic fishes Argyropelecus and Maurolicus. This activity is equivalent for both fishes when reported to the protein content as is their O₂ consumption.
• 2.2. The activity is optimal at pH 6.8–7.5. It is not specific for ATP since GTP, ITP, UTP and CTP are also hydrolyzed to a significant extent. It is also not specific for Mg²⁺, the activity being equivalent (Argyropelecus) or higher (Maurolicus) with Ca²⁺ and high also with Co²⁺ and Mn²⁺
• 3.3. Twenty to 30 per cent of the activity measured at pH 7.4 is probably due to the mitochondrial ATPase as it is shown by oligomycin and venturicidin inhibition.
• 4.4. Activities of both fishes photophores are partly inhibited by N-N'-dicyclohexylcarbodiimide (DCCD), azide, LaCl₃, vanadate, diethylstilbestrol (DES) and N-ethylmaleimide (NEM) which are all inhibitors of ionic pumps.
• 5.5. Argyropelecus activity is sensitive to ouabaïn.
• 6.6. Our results show the presence of ionic pumps in Argyropelecus and Maurolicus photophores. If there is evidence for the absence or very low activity of a H⁺ pump, it is sure that Argyropelecus at least possess a Na⁺K⁺-ATPase.
• 7.7. The significance of a high protein content in Maurolicus photophores and of a large inorganic phosphate concentration in Argyropelecus is discussed.

     

Synaptic interaction between the giant interneuron and the giant motorneuron in the hermit crab,Pagurus pollicarus

• 1.1. An anatomical and physiological investigation was made of several components in the withdrawal escape response of the hermit crab, Pagurus pollicarus.
• 2.2. In the fused last thoracic-first abdominal ganglion, the giant axon (GA) synapses with the giant motor (GM) neuron which innervates the abdominal flexor muscles.
• 3.3. The synapse is unidirectional, conducting impulses only from the GA to the GM.
• 4.4. The synaptic delay time is less than 0.4 msec.
• 5.5. Concentrations of MgCl₂ and MnCl₂ which normally block chemical synapses were ineffective in interfering with GA-GM transmission.
• 6.6. The GA-GM synapse was reversibly blocked by 0.5 mM DNP.
• 7.7. It is concluded that GA-GM connection is a rectifying electrical synapse.

     

Does schooling reduce fast-start response latencies in teleosts?

• 1.1. Response latencies, denned as the time between a d.c. electric shock and initiation of a fast-start (startle response) were measured for eight species of teleosts.
• 2.2. Fast-start response latencies varied from 10 to 36 cm. Highest values were found for individuals of two solitary species, Etheostoma caeruleum and Cottus cognatus. Lowest values were found for Esox and Salwo gairdneri.
• 3.3. Schooling in Perca flavescens, Lepomis macrochirus and Pimephales promelas significantly reduced fast-start response latencies by 7–16 msec. A 4 msec. reduction for Notropis cornutus was not significant.
• 4.4. No reduction in fast-start response latency was found for Pimephales promelas given the illusion of a school or for individuals greater than 15 cm from a school.
• 5.5. The observed variation in fast-start response latency would favour attack success of predators and escape success for schooled, but not solitary, presumptive prey.

     

Alteration of the protein composition of bothrops jararaca venom and venom gland by isoproterenol treatment

• 1.1. The protein composition of Bothrops jararaca venom and venom gland was analyzed through SDS-PAGE, after isoproterenol (IPR) treatment.
• 2.2. Some proteins (47, 48, 57 and 72 kDa) were detected in the gland homogenate from the control but not from the IPR-treated samples.
• 3.3. Three proteins (26.5, 44.5 and 53 kDa) were detected in the venom gland from IPR-treated snakes but not from the venom gland from the control.
• 4.4. In the venom samples proteins of 41 and 74 kDa were detected only in the IPR treated samples, while proteins of 17 and 28 kDa were detected only in the control.
• 5.5. The biological activity of the venom did not change with IPR treatment.

     

The UDP-galactose 4-epimerase of the albumen gland of Lymnaea stagnalis and the effects of photoperiod,starvation and trematode infection of its activity

• 1.1. Kinetic aspects of the enzyme UDP-galactose 4-epimerase in crude homogenates of the albumen gland of the snail Lymnae stagnalis were estimated. The mean values of the Km for UDP-galactose and for NAD are 0.343 and 0.097 mM, respectively. The enzyme is inhibited by NADH. It is inactivated by freezing and raised temperature (25°C), but it can be reactivated by NAD.
• 2.2. In the albumen gland the epimerase activity is 10–100 times higher than in other tissues, reflecting the high turnover of glucose to galactose, essential for the synthesis of galactogen in this organ.
• 3.3. In fed snails long day conditions stimulates albumen gland epimerase activity, coinciding with high egg production.
• 4.4. In starved snails a fairly high residual activity of the enzyme is maintained, irrespective of photoperiod or egg production.
• 5.5. Trematode infection leads to a considerable reduction of the epimerase activity.
• 6.6. The results indicate that the epimerase activity in fed snails, when the gland shows a regular release, reflects long-term adaptations (photoperiod). In starved and parasitized snails, when no regular release or product occurs, a basic epimerase activity is maintained. This might be important for a rapid restoration of egg production after the termination of adverse conditions.

     

Morphology and electrophysiological characteristics of caudodorsal cells of Lymnaea stagnalis in dissociated cell culture

• 1.1. The neuroendocrine caudodorsal cells (CDCs) of Lymnaea stagnalis are a network of about 100 electrotonically coupled neurones. The CDCs release multiple peptides, including an ovulation hormone, during a period of electrical activity, the CDC-discharge.
• 2.2. In isolated brains, a similar period of electrical activity (the afterdischarge) can be induced in all CDCs by a period of intracellular repetitive suprathreshold stimulation of one CDC.
• 3.3. In order to study the regulation of this electrical behaviour in the absence of electrical interactions and in a controlled environment, experiments were performed on CDCs in dissociated cell culture.
• 4.4. Methods for isolation and cell culture are described. Cell cultures had long-term viability and outgrowth of neurities occurred under serum-free conditions.
• 5.5. CDCs in cell culture maintained their capability of producing afterdischarges upon electrical stimulation. Cells in culture appeared more excitable than cells in the intact isolated brain.
• 6.6. The characteristic responses of CDCs in intact isolated brains to acetylcholine and FMRFamide were preserved in cultured CDCs. Both agents induced a transient hyperpolarization of the membrane, inexcitability and inhibition of an ongoing discharge.
• 7.7. In experiments where isolated CDCs were closely apposed, but physically separate, it was found that an afterdischarge in one CDC could induce a discharge in the other CDC.
• 8.8. These results confirm previous results which showed that an excitatory factor is released from the brain during the afterdischarge (Ter Maat et al., 1988, Brain Res., 43, 77–82), and demonstrate that this excitatory factor is released from the CDCs themselves.

     

Evidence of an egg-laying factor in the prostatic secretions of Helix aspersa müller

• 1.1. A high percentage (53%) of isolated snails injected with prostate gland homogenates lay eggs.
• 2.2. These egg masses consist of a few eggs which contain many nonviable oocytes.
• 3.3. Preliminary experiments suggest that an egg-laying factor may be present in prostatic secretions.
• 4.4. Snails bred in isolation from hatching, whether injected or not, occasionally lay viable eggs.
• 5.5. This observation shows that self-fertilization or parthenogenesis is, in fact, possible in Helix aspersa Müller.

     

The dufour gland substances of the workers of Formica fusca and Formica lemani (hymenoptera: formicidae)

• 1.1. The Dufour gland secretions of Formica fusca consist mainly of saturated straight and branched chain hydrocarbons (C₉–C₁₉), one unsaturated hydrocarbon (C₁₃) and two sesquiterpenoids, farnesene and homofarnesene.
• 2.2. In F. lemani, the Dufour gland contains branched, saturated and unsaturated hydrocarbons (C₉–C₁₉) and two farnesenes.
• 3.3. The two species were distinguished chiefly by the presence of a relatively large proportion of farnesene in F. fusca, with very little homofarnesene and by contrast, little farnesene but much more homofarnesene in F. lemani.
• 4.4. The contents of the Dufour gland can be used as a chemotaxonomic clue to distinguish between the species.

     

Comparative analysis of dufour's gland secretions of two carpenter bees (xylocopinae: anthophoridae) with different nesting habits

• 1.1. The chemistry and function of Dufour's gland secretions of two carpenter bees were studied.
• 2.2. Dufour's gland of Proxylocopa olivieri, a ground nesting bee, produces long chain hydrocarbons that are utilized to line its brood cells and are mixed with its bee bread.
• 3.3. Dufour's gland secretion of Xylocopa sulcatipes, on the other hand, is dominated by ethyl eicosanoate and ethyl docosanoate accompanied by the corresponding methyl esters and high boiling hydrocarbons.
• 4.4. This wood nesting bee apparently does not use Dufour's gland secretion to line its nest.
• 5.5. The relationship between the respective chemistry and function of Dufour's gland secretion and the nesting ecology of the two bees is discussed.

     

Phosphatase activity in the hepatopancreas of Helix aspersa

• 1.1. Phosphatase acid (PhA) activity in the digestive gland (hepatopancreas) of the common garden snail Helix aspersa has been investigated using cytochemical methods.
• 2.2. All the cells composing this gland show PhA activity, the distribution pattern differing according to the cell type.
• 3.3. The digestive cells show the most widely distributed reaction product (brush border, phagolysosomes, multivesicular bodies and autophagic vacuoles).
• 4.4. In the excretory cells this activity appears in large sacs, while in the calcium cells the reaction product is abundant in the calcium granules.
• 5.5. Cellular digestion processes performed by each of these cell types is discussed together with their role in the detoxification of heavy elements derived from the environment.

     

Electric organ discharge frequency modulation evoked by water vibration in Gymnotus carapo

• 1.1. The electric organ discharge (EOD) frequency modulations evoked by brief water vibration were analysed in the pulse-type fish Gymnotus carapo.
• 2.2. The response consisted of a transient increase of the EOD frequency at short latency (30 msec). Response profiles were characteristic of the specimen and relatively independent on stimulus intensity.
• 3.3. Conversely, they were dependent on stimulation sequence, showing a rapid decrement along successive stimuli and high temporal discrimination.
• 4.4. The brief latencies indicate a relatively simple neural circuit.
• 5.5. The response may be an electrolocation enhancement strategy for the detection of moving objects based on “sampling” the periphery at a higher frequency.

     

Application of electrical analogs to metabolic control analysis: Linear pathways with multiple feedback

• 1.1. Using electrical analogs, we have presented a systematic procedure for calculating the flux control coefficients of linear metabolic pathways with multiple feedback loops.
• 2.2. In this method, an electrical analog circuit is constructed first for the unregulated pathway.
• 3.3. This circuit is subsequently modified in a step-by-step fashion to take into account the effect of each feedback loop in the pathway.
• 4.4. An analog circuit consists of resistances which are connected in series (or parallel) with a voltage (or current) source.
• 5.5. The flux control coefficients of the enzymes are represented by voltages across (or currents through) the resistances and are determined by an application of Ohm's law.
• 6.6. We have investigated the possible patterns in linear pathways with two feedback loops.
• 7.7. This is followed by an analysis of a linear pathway with an arbitrary pattern of feedback inhibition.

     

Adaptation in Helix pomatia neurons

• 1.1. Spike frequency adaptation has been studied on neurons of Helix pomatia subesophageal ganglia and interpreted by means of a behavioural model describing the phenomenon in neurons either silent or autorhythmic at rest.
• 2.2. At low stimulating currents the initial discharge frequency F(0) is linearly related to the current strength G.
• 3.3. In the linearity range F(0)/G each neuron was characterized by means of four model parameters: the proportionality constant between F(0) and G, the decay constant of the frequency, the inhibitory current from a single nerve impulse and the decay time constant of the inhibitory current.
• 4.4. The four parameters varied in different cells with a range of 0.18–4.98 Hz/nA, 1.02–3.85 sec, 0.05–0.95 nA and 1.74–22.33 see, respectively.
• 5.5. Experimental results have been analyzed considering inhibitory current, electrogenie sodium pump and other proposed adaptation parameters.

     

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Serotonin or electrical optic nerve stimulation increases the photosensitivity of the Aplysia eye

• 1.1. Exposure of isolated Aplysia eyes to serotonin (10⁻⁷ M) produces large and long-lasting (hours) increases in the ERG recorded from the surface of the eye.
• 2.2. Dopamine, octopamine, or acetylcholine do not mimic the effect of 5-HT on the ERG.
• 3.3. Brief electrical optic nerve stimulation (2 Hz, 2 min) also increases the ERG and this effect also lasts a long period of time (0.5–2 hr).
• 4.4. Our results suggest that serotonin increases the response of photoreceptor cells to light and that efferent optic nerve activity may modulate photosensitivity through release of serotonin in the eye.

     

Comparative nuclear magnetic resonance studies of diffusional water permeability of red blood cells from different species. V—Rabbit (Oryctolagus Cuniculus)

• 1.1. The diffusional water permeability (P_d) of rabbit red blood cell (RBC) membrane has been monitored by a doping nuclear magnetic resonance (NMR) technique on control cells and following inhibition with p-chloromercuribenzene sulfonate (PCMBS).
• 2.2. The values of P_d were around 6.3 × 10⁻³ cm/sec at 15°C, 7.0 × 10⁻³cm/sec at 20°C, 8.0 × 10⁻³ cm/sec at 25°C, 9.1 × 10⁻³ cm/sec at 30°C and10.7 × 10⁻³ cm/sec at 37°C.
• 3.3. Systematic studies on the effects of PCMBS on water diffusion indicated that the maximal inhibition was reached in 15 min at 37°C with 0.5 mM PCMBS.
• 4.4. The values of maximal inhibition were around 71–74% at all temperatures.
• 5.5. The basal permeability to water was estimated as 1.6 × 10⁻³cm/sec at 15°C, 2.0 × 10⁻³cm/sec at 20°C, 2.4 × 10⁻³cm/sec at 25°C, 2.6 × 10⁻³cm/sec at 30°C, and 3.1× 10^{−3 cm/secat 37°C}.
• 6.6. The activation energy of water diffusion was around 18 kJ/mol and increased to 27 kcal/mol after incubation with PCMBS in conditions of maximal inhibition of water diffusion.
• 7.7. The membrane polypeptide electrophoretic pattern of rabbit RBCs has been compared with its human counterpart.
• 8.8. The rabbit membrane contained a higher amount of spectrin (bands 1 and 2), while the band 6 (glyceraldehyde-3-phosphate dehydrogenase) was markedly less intense.
• 9.9. Considerable differences in the electrophoretic patterns of the two sources of RBC membranes appeared in the bands migrating in the band 4.5 region and in front of band 7, where some polypeptides were apparent in higher amounts in the rabbit RBC membrane.

     

Water diffusion,ion transport and lipid composition of the skin of Rana cyanophlyctis Schneider under osmotic stress

• 1.1. Analysis of the total lipid content (TL), components of the neutral lipid fraction (NLF), phospholipid fraction (PLF), recordings of electrical potential differences and diffusional permeability were carried out in the skin of the aquatic frog Rana cyanophlyctis subjected to in vivo salt stress (0.9 sodium chloride) for different durations (0, 1, 3 and 7 days).
• 2.2. A general decrease of skin TL and of components of the NEE and PEE was observed.
• 3.3. Stoichiometric ratios for skin PLF components under initial salt stress of different durations reveal an increase of the ratios of sphingomyelin and phosphatidyl choline after osmotic stress.
• 4.4. The diffusional permeability of water increased following exposure to salt stress of I, 3 and 7 days duration.
• 5.5. The transepithelial potential difference measured in vitro after a salt stress of 3 days was considerably higher than the controls.

     

The influence of optic nerve section on blood metabolite levels in Carcinus maenas (Crustacea: Brachyura)

• 1.1. Blood metabolite levels were assayed in Carcinus maenas as an indicator of the functioning of the hyperglycemic hormone, HGH, secreted by the crab's eyestalk neuroendocrine tissue.
• 2.2. Bilateral eyestalk ablation eventually resulted in a hypoglycemic response after 2–3 days.
• 3.3. Bilateral optic nerve section produced a significant, long-term hypoglycemic response suggesting that release of HGH from the eyestalk sinus gland is controlled, via a promotive neural pathway, by the CNS and probably by the cerebral ganglia.
• 4.4. Injection of eyestalk extract into operated crabs consistently produced significant, short-term hyperglycemia.