Intracellular free sodium and potassium, post-carbachol hyperpolarization, and extracellular potassium-undershoot in rat sympathetic neurones

Double-barrelled ion-sensitive microelectrodes were used to record the free intracellular Na+- and K+-concentrations ([Na+]i, [K+]i) and to determine their relation to changes in membrane potential and extracellular K+ ([K+]e) in rat sympathetic ganglia. The application of 50 μmol/l carbachol resulted in an elevation of [K+]e followed by a post-carbachol [K+]e-undershoot. The membrane depolarization of the sympathetic neurones was associated with an increase in [Na+]i and a decrease in [K+]i. A membrane hyperpolarization and a recovery of [K+]i and [Na+]i to their baseline levels were observed during the [K+]e-undershoot. The time course of the [K+]e-undershoot correlated exactly with the duration of the rise in [Na+]i and decrease of [K+]i. No K+-reuptake occurred in the presence of ouabain. These data confirm, by direct measurements of intracellular ion concentration changes, the contribution of the Na+, K+-pump to the post-carbachol membrane hyperpolarization and [K+]e-undershoot

MUSCULAR ACTIVITY IN THE STRETCH-SHORTENING CYCLE (SSC): NOT ONLY MAXIMIZATION BUT OPTIMIZATION IS NECESSARY

INTRODUCTION: Drop jumping is a very complex skill with a stretch-shortening cycle (SSC) involving several phases – preparation for landing, landing itself, shock absorption and push-off. Only a very short span of time (£ 200ms) is available for the execution of a drop jump. For this reason much is required of the jumper’s neuromuscular system. Especially an EMG reduction of m. gastrocnemius activity just before and at the beginning of landing has been reported several times (Schmidtbleicher/Gollhofer, 1985). This reduction has been interpreted as a mechanism to protect the muscle from excessive stretch loads. Previously, only qualitative results have been reported. METHODS: Reactive capabilities were analyzed in two complex studies of 18 sport students. The following movements were studied: squat jumps, countermovement jumps and drop jumps from drop heights of 16, 24, 32, 40, 48 and 56 cm. EMG-activities of the m. tibialis anterior, m. soleus, m. gastrocnemius and m. rectus femoris were registered to describe muscle activity during vertical jumping. Simultaneously, ground reaction forces and changes in knee angle were registered. A new method was developed for measuring the EMG-reduction of m. gastrocnemius. RESULTS: In these studies it could be observed that EMG reduction of m. gastrocnemius occurs simultaneously with the maximal innervation of m. rectus femoris. Strong action in the knee joint is demonstrated by the activity of the leg extensor m. rectus femoris, which is needed to stop downward movement and to start the push-off. The m. gastrocnemius´ activity with its antagonistic effect on the knee joint was reduced when m. rectus femoris activity started, and reached maximal innervation significantly later than m. rectus femoris during ground contact. This is especially the case for good jumpers. After a training period of four weeks (only reactive movements) this program of innervation could be observed in almost all the participants in these studies. CONCLUSION: The results show that the EMG-reduction of m. gastrocnemius during drop jumping cannot be considered a reliable mechanism to protect the muscle from excessively large stretch loads, but that this EMG activity of the antagonistic muscles makes possible an optimal intermuscular coordination for drop jumping. REFERENCES: Schmidtbleicher, D.; Gollhofer, A. (1985). Einflußgrößen des reaktiven Bewegungsverhaltens und deren Bedeutung für die Sportpraxis. In: Bührle, M. (1985). Grundlagen des Maximal- und Schnellkrafttrainings, 271-281

Role of protein kinase C in inhibition of renin release caused by vasoconstrictors

It was the aim of the present study to get insight into some of the intracellular mechanisms by which the vasoconstrictor hormones angiotensin II (ANG II), arginine vasopressin (AVP), and norepinephrine (NE) inhibit renin release from renal juxtaglomerular cells. To this end a primary cell culture from rat renal cortex was established that consisted of 50% juxtaglomerular cells. The cultured juxtaglomerular cells contained prominent renin granules closely resembling those in the intact kidney and responded to a number of stimuli of renin release. By using these cultures, we found that ANG II (10(-7) M), AVP (10(-6) M), and NE (10(-5) M) inhibited renin release and increased the calcium permeability of the plasma membrane of the cultured cells. Both the effects on renin release and on calcium permeability could be diminished or even be abolished by the calcium channel blocker verapamil (Vp) (10(-5) M). ANG II, AVP, and NE led to an increased formation of diacylglycerol (DAG), a well-known stimulator of protein kinase C (PKC). Moreover, a direct stimulation of PKC by 12-O-tetradecanoylphorbol-13-acetate (TPA) (10(-8)-10(-6) M) also inhibited renin release and increased the calcium permeability of the cell membrane. Similar to ANG II, AVP, and NE, the effects of TPA on calcium permeability and renin release could be diminished by Vp. In conclusion, these results point toward a common mechanism by which vasoconstrictors inhibit renin release from renal juxtaglomerular cells: ANG II, AVP, and NE activate a phospholipase C, which generates DAG.(ABSTRACT TRUNCATED AT 250 WORDS

Thomas Hobbes: sobre el miedo

Este trabajo pretende echar cierta luz sobre el papel del miedo en el pensamiento político de Hobbes. Sabido es que esta pasión subyace al contrato social, en el sentido de que impulsa al hombre a abandonar el estado de naturaleza a fin de encontrar seguridad y de deshacerse de la amenaza de la muerte violenta. Teniendo en cuenta que el miedo y la muerte son inseparables en la filosofía de Hobbes, surge una pregunta fundamental: ¿hasta qué punto podemos decir que el miedo desaparece completamente después del contrato social? En Hobbes, el miedo parecería ser una característica intrínseca del hombre.This work intend to draw some light upon the role of fear in Hobbes?s political thought. It s known that this passion underlies the social contract, in the sense that it drives man to leave the state of nature in order to find security, and also to get rid of the menace of violent death. Taking into account that fear and death are inseparable in Hobbes s philosophy, a fundamental question arises: to what extent can we say that fear vanishes completely after social contract? In Hobbes, fear seems to be an intrinsical feature of men.Departamento de Filosofí

Do tax loss restrictions distort venture capital funding of start-ups?

Anti-tax loss trafficking rules disallow the use of loss carryforwards after a change in ownership or activity (such as significant changes in turnover, employment, or the product portfolio). This restriction could threaten accumulated loss carryforwards of start-ups. Accounting for the increased risk and reduced return on their investment, VC investors could reduce their funding. I analyze whether the venture capital (VC) funding of start-ups in Europe is affected by these regulations. I base my empirical analysis on several case studies and a panel analysis covering VC- funded companies in the EU28 Member States from 1999 to 2014. My findings suggest that strict anti-tax loss trafficking rules indeed impair VC funding. Especially more mature companies and companies in high-tech industries are affected

Tax law and the transfer of start-up losses: a European overview and categorization

Most of the European Member States employ anti-loss trafficking rules. They aim to prevent the acquisition of mere corporate shells with high tax loss carryforwards for the tax asset to be utilized in profitable companies. However, other corporations can unintentionally be affected by the anti-abuse regulations if there is a change in ownership or activity. The transfer restrictions have been argued to impair start-up financing, as investors are faced with the risk of losing accumulated loss carryforwards in the corporation upon the entering of new or the capital increase of existing investors. This study provides an overview over the design and development of loss transfer restrictions in the EU28 over a time period of 19 years (2000 – 2018). Different aspects of the regulations are analyzed against the background of their impact on start-ups. Finally, the rules are categorized with respect to their strictness. Over time, more countries introduced restrictions. At the same time, the regulations became more lenient, offering start-ups more opportunities to maintain their loss carryforwards and, therefore, decreasing the risk for investors

Excitatory amino acids and intracellular pH in motoneurons of the isolated frog spinal cord

Double-barrelled pH-sensitive micro-electrodes were used to measure changes of intracellular and extracellular pH in and around motoneurons of the isolated frog spinal cord during application of excitatory amino acids. It was found that N-methyl- -aspartate, quisqualate and kainate produced a concentration-dependent intracellular acidification. Extracellularly, triphasic pH changes (acid-alkaline-acid going pH transients) were observed during the action of these amino acids. The possible significance of such pH changes for the physiological and pathophysiological effects of excitatory amino acids are discussed

Too much "skin in the game" ruins the game: Evidence from managerial capital gains taxes

Co-investment, often seen as a remedy for agency problems, may incentivize managers to cater to own preferences. We provide evidence that mutual fund managers with considerable co-investment stakes alter risk-taking decisions to prioritize their own tax interests. By exploiting the enactment of the American Taxpayer Relief Act 2012 as an exogenous shock of managerial capital gains taxes, we observe that co-investing fund managers increase risk-taking by 8%. Specifically, these managers adjust their portfolios by investing in stocks with higher beta. The observed effect appears to be driven by agency incentives, particularly for funds with a more convex flow-performance relationship and for managers who have underperformed. Such tax-induced behavior is associated with negative fund performance. We highlight the role of co-investment in transmitting managerial tax shocks to mutual funds