Matti Järvilehto

Tuning of photoreceptor spectral sensitivity in fireflies (Coleoptera: Lampyridae)

Abstract Sexual communication between male and female fireflies involves the visual detection of species-specific bioluminescent signals. Firefly species vary spectrally in both their emitted light and in the sensitivity of the eye, depending on the time when each is active. Tuning of spectral sensitivity in three firefly species that occupy different photic niches was investigated using light and electron microscopy, microspectrophotometry, and intracellular recording to characterize the location and spectral absorption of the screening pigments that filter incoming light, the visual pigments that receive this filtered light, and the visual spectral sensitivity. Twilight-active species had similar pink screening pigments, but the visual pigment of Photinus pyralis peaked near 545 nm, while that of P. scintillans had a λmax near 557 nm. The night-active Photuris versicolor had a yellow screening pigment that was uniquely localized, while its visual pigment was similar to that of P. pyralis. These results show that both screening and visual pigments vary among species. Modeling of spectral tuning indicates that the combination of screening and visual pigments found in the retina of each species provides the best possible match of sensitivity to bioluminescent emission. This combination also produced model sensitivity spectra that closely resemble sensitivities measured either with electroretinographic or intracellular techniques. Vision in both species of Photinus appears to be evolutionarily tuned for maximum discrimination of conspecific signals from spectrally broader backgrounds. Ph. versicolor, on the other hand, appears to have a visual system that offers a compromise between maximum sensitivity to, and maximum discrimination of, their signals.

Effects of different training protocols on Ca2+ handling and oxidative capacity in skeletal muscle of Atlantic salmon (Salmo salar L.)

SUMMARY The modulation of calcium channel density and oxidative capacity in skeletal muscle after different training protocols were studied in 3-year-old Atlantic salmon smolts. The effect of endurance exercise on dihydropyridine (DHP) and ryanodine (Ry) receptor densities as well as on muscle metabolism were determined by immunoblot and histochemical analysis from swimming muscles of fish subjected to nine different training protocols varying in duration and water current velocity. In general, exercise training caused a significant increase in the density of both DHP and Ry receptors in both muscle types studied. In red muscle, the most notable increase in DHP and Ry receptor expression was observed in muscle sections from fish swimming against intermediate current velocity for a 2-week period (182.3±16.3%, 234.6±30.3%, respectively). In white muscle, the expression of DHP and Ry receptors was most upregulated after a 6-week swimming period also at intermediate water current velocity (270.4±23.9%, 114.4±15.3%, respectively). As with the activity of enzymes involved in muscle energy supply, endurance exercise resulted in a significant increase in succinate dehydrogenase (SDH) activity, but a significant decrease in phosphorylase activity. We conclude that the expression of both DHP and Ry receptors was upregulated in the swimming muscles of salmon as a consequence of exercise training. This, along with the increased oxidative enzyme activity, provides benefits to the contraction efficiency of fish muscles while swimming. However, it was also observed that optimal oxidative swimming capacity is achieved only with a proper exercise program, since the most relevant changes in DHP and Ry receptor expression, as well as in oxidative capacity, were seen in the group training with the intermediate swimming velocity.

Comparative analysis of mouse skeletal muscle fibre type composition and contractile responses to calcium channel blocker

BackgroundIn this study, we examined the correlation between excitation-contraction coupling characteristics and skeletal muscle fibre type by (1) localizing the distribution of dihydropyridine receptor (DHPR) protein and (2) comparing the effect of DHPR blocker on muscles with different fibre type composition, in order to better understand the differences between contractile phenotypes of fibres and to explain the contradictory reports to date on the interaction of dihydropyridines with skeletal muscle isoform of DHPR.ResultsHistochemical experiments revealed that fluorophore conjugated dihydropyridines stain selectively the membranes of muscle fibres. The staining was most evident in type IIA fibres. The major fibre type in gluteus and femoris, revealed by mATPase staining, was IIA (45.0 and 38.1 %, respectively). In gastrocnemius the content of IIA fibres was 22.7 %. Contraction forces before and after the addition of blocker for the three muscles investigated were: gluteus 0.075 ± 0.017 N vs. 0.052 ± 0.011 N, femoris 0.045 ± 0.005 N vs. 0.033 ± 0.005 N and gastrocnemius 0.089 ± 0.016 N vs. 0.075 ± 0.014 N, respectively. The attenuation of contraction force proportional to the cross-sectional area of the muscle was significantly (P = 0.023) higher in gluteus (28.3 ± 3.5 %) and femoris (27.6 ± 3.2 %) as compared to gastrocnemius (16.1 ± 2.5 %). However, no significant change in the control measurements was observed ruling out the possibility of fatigue.ConclusionThe results indicate that the attenuation of the contraction force was largest in muscles with a high percentage of type IIA fibres. This supports our finding that the abundance of dihydropyridine receptors of IIA fibres outnumbers that in the other fibre types. The present data show that the correlation of density of dihydropyridine receptors can be one of the important factors influencing the overall contractile properties of the muscle and for its part explain the contradictory results of previous studies on coupling process.

Effects of training on functional variables of muscles in reared Atlantic salmon Salmo salar smolts : connection to downstream migration pattern

The relative amount of muscle contraction regulating dihydropyridine and ryanodine receptors in the swimming muscles of trained reared Atlantic salmon Salmo salar smolts was compared with those of untrained and wild smolts. After an optimized 2 week training period, i.e. swimming with a velocity of 1·5 body lengths per second for 6 h per day, the level of both receptors was significantly higher in the muscles of trained S. salar than in the untrained ones before they were released into the natural environment. This difference persisted after downstream migration in the river. The highest level of receptors was observed in wild S. salar. Swimming performance was also higher in trained fish compared to untrained ones. Furthermore, swimming performance was positively associated with the level of receptors in both red and white muscle types. Downstream migration after release into the wild was significantly slower in trained smolts than in untrained fish. This indicates that trained smolts were most probably swimming harder against the current in the river than untrained smolts. The possible advantages for a slower migration in the river are discussed. This study shows that the prerequisites for effective contraction of the swimming muscles are better met in trained S. salar compared to untrained fish, and the muscles of trained smolts more closely resemble those of wild smolts. The results also imply that the capacity of untrained, reared smolts to swim against the current is not equal to that of their trained or wild counterparts which affects the downstream migration pattern of S. salar smolts.

Vasa vasorum hypoxia: Initiation of atherosclerosis

We propose a new hypothesis pointing of a functional hypoxia in vasa vasorum, which might explain the initiation and the early development of the atherosclerosis in the deep layer of intima. Since vasa vasorum are end arteries, they easily develop hypoxia and/or ischemia in the cells of intima or media of arterial wall. The most vulnerable sites for hypoxia are the arterial bifurcations due to the anatomical and physiological reasons. They are also known to be the most common sites of atherosclerosis. The known risk factors for atherosclerosis, high blood pressure and nicotine, reduce the blood flow in the end branches of the vasa vasorum. The local ischemia will affect the endothelial cell structure and causes a local inflammation, which, in turn, makes it permeable to large particles such as microbes and LDL-lipoproteins and other fatty acids, which are phagocytozed by macrophages transforming them into foam cells. The present hypothesis explains most problems of the previous theories and offers a logical sequence of the events involved in the development of atherosclerosis.

Polarization sensitivity of individual retinula cells and neurons of the flyCalliphora

SummaryLocalized intracellular light-evoked potentials were recorded from the retina of the flyCalliphora erythrocephala by means of very fine tapered glass capillary microelectrodes.In the retinula cell layer both polarization sensitive and insensitive short visual cells (R1–6) were found. In the lamina, all R1–6-fibers studied were insensitive to the E-vector. In the soma of the R7-cell no polarization sensitivity was found, and the characteristic curve of this cell, based on soma recordings, was almost identical to that of the visual fibers R1–6. The second order neurons (L1 and L2) studied neither could detect the direction of the E-vector of polarized light.No spike-activity was obtained.

Expression of L-type calcium channels associated with postnatal development of skeletal muscle function in mouse

Several factors have an influence on the improvement of muscle activity and motor co-ordination of mammals during post-natal development. One of them is voltage sensitive L-type calcium channel function. In striated muscles of adult mammals these channels are located in T-tubule membranes thus linking the on-coming action potential to the molecular process of muscle contraction. The postnatal development of L-type calcium channels is therefore critical not only for contraction but also for all subsequent motor learning. We used high affinity enantiomer of dihydropyridine labelled with a fluorophore in order to show the relative amount of L-type calcium channels by histofluorescence in tissue. We found by qualitative microscopical analysis that the amount of L-type calcium channels increased during the postnatal development in the mouse skeletal muscle (m. rectus femoris and m. gastrocnemius). We also noted variation between different fibre types in the increase of the amount of L-type calcium channels, as judged by the intensity of histofluorescence. We showed by histochemical staining and statistical analysis that the high density of L-type calcium channels in adult muscles is correlated with fast oxidative glycolytic fibre type of striated muscles rather than slow oxidative or fast glycolytic fibres. Based on this finding we propose that the development of L-type calcium channels can be considered as one of the factors determining the different physiological properties of fibre types.

Effects of low-intensity training on dihydropyridine and ryanodine receptor content in skeletal muscle of mouse

To evaluate low-intensity exercise training induced changes in the expression of dihydropyridine (DHP) and ryanodine (Ry) receptors both mRNA and protein levels were determined by quantitative RT-PCR and immunoblot analysis from gastrocnemius (GAS) and rectus femoris (RF) muscles of mice subjected to a 15-week aerobic exercise program. The level of muscular work was assayed by changes in myosin heavy chain (MHC) content, myoglobin (Mb) expression and muscle size. The mRNA expression and optical density of DHP receptor increased significantly in GAS by 66.8 and 39.5%, respectively. The expression of Ry receptor, on the other hand, was not up-regulated. In RF, there was a significant increase of 38.4% in the mRNA expression of DHP receptor, although the protein level remained the same. No changes in Ry receptor expression was observed. The training resulted in a 1.58% increase in the amount of MHC IIa and a 2.34% decrease in that of IIb and IId in GAS. A significant 8.3% increase in the Mb content was observed. In RF, no significant changes in MHC or in Mb content were noted. Our results show that an evident increase in the mRNA and protein expression of DHP receptor was induced in GAS even by a relatively low-intensity exercise. Surprisingly, contrast to DHP receptor expression, no changes in Ry receptor mRNA, or protein levels were found, indicating more abundant demand for DHP receptor after increased muscle activity.ResumenPara evaluar los cambios inducidos en la expresión de los receptores de dihidropiridina (DHPR) y rianodina (RyR) por el entrenamiento con ejercicio de baja intensidad, se determinan los niveles de mRNA y de proteína mediante el análisis de RT-PCR cuantitativa e inmunoblot de los músculos gastrocnemius (GAS) y rectus femoris (RF) de ratón sometido a un programa de ejercicio aeróbico durante 15 semanas. El nivel de trabajo muscular fue determinado por los cambios en contenido de cadena pesada de miosina (MHC), expresión de mioglobina (Mb) y tamaño del músculo. La cantidad de mRNA y de proteína de DHPR aumentó significativamente en un 66,8 y 39,5% respectivamente. La expresión de RyR, por otro lado, no se vio incrementada. En RF hubo un aumento significativo del 22,7% en la expresión del mRNA de DHPR, aunque los niveles de proteína permanecieron inalterados. Tampoco se observaron cambios en la expresión de RyR en RF. El entrenamiento dio lugar a un aumento del 1,58% en la cantidad de MHC IIa y disminución del 2,34% en MHC IIb y IId en GAS, con incremento significativo del 8,3% en el contenido de Mb. En RF no se detectaron cambios significativos en el contenido en MHC ni en Mb. Nuestros resultados muestran que se induce un evidente aumento en el nivel de RNAm y de proteína DHPR en GAS mediante un ejercicio de relativamente baja intensidad. Sorprendentemente, en contraste con la expresión de DHPR, no se encontraron cambios en los niveles de mRNA ni de proteína de RyR, indicando mayor demanda de DHPR al incrementar la actividad muscular.

Expression of Dihydropyridine and Ryanodine Receptors in Type IIA Fibers of Rat Skeletal Muscle

In this study, the fiber type specificity of dihydropyridine receptors (DHPRs) and ryanodine receptors (RyRs) in different rat limb muscles was investigated. Western blot and histochemical analyses provided for the first time evidence that the expression of both receptors correlates to a specific myosin heavy chain (MHC) composition. We observed a significant (p=0.01) correlation between DHP as well as Ry receptor density and the expression of MHC IIa (correlation factor r=0.674 and r=0.645, respectively) in one slow-twitch, postural muscle (m. soleus), one mixed, fast-twitch muscle (m. gastrocnemius) and two fast-twitch muscles (m. rectus femoris, m. extensor digitorum longus). The highest DHP and Ry receptor density was found in the white part of m. rectus femoris (0.058±0.0060 and 0.057±0.0158 ODu, respectively). As expected, the highest relative percentage of MHC IIa was also found in the white part of m. rectus femoris (70.0±7.77%). Furthermore, histochemical experiments revealed that the IIA fibers stained most strongly for the fluorophore-conjugated receptor blockers. Our data clearly suggest that the expression of DHPRs and RyRs follows a fiber type-specific pattern, indicating an important role for these proteins in the maintenance of an effective Ca2+ cycle in the fast contracting fiber type IIA.

A digital feedback controller application for studying photoreceptor adaptation by ‘voltage clamp by light’

We present a new digital feedback application for the study of the sensitivity characteristics of photoreceptors. The amplitude of the recorded membrane voltage of a cell is steered by changing the incoming light intensity with a motor-driven circular, linear neutral-density wedge (CFW). The voltage response is sampled and fed to a software position controller of the CFW. The controller determines the position of the wedge according to the desired (command) value of the response. The light intensity changes during steady-state represent the sensitivity change, the time-course of adaptation.