SUMMARY1. Voltage-clamp experiments using the three micro-electrode method were performed to study the temperature dependence of the calcium current ICa in intact twitch skeletal muscle fibres of the frog. Contraction was blocked by recording in hypertonic sucrose solutions.2. For depolarizations smaller than 0 mV the decay of the transient, slow, inward current, recorded in the presence of external tetraethylammonium (TEA+) and by replacing Cl-for CH3SO3-, followed a complex time course. For larger depolarizations, after the initial inward current, there was a prominent, slow, outward current which showed two phases: after reaching a peak (time to peak 1-0 sec, peak amplitude 20-50 #sA/cm2 at 20 mV) it slowly declined to a steady level in about 2-3 see at 23 'C.3. The inward current was greatly reduced or abolished by the adding of2 mM-Cd2+ or by replacing external Ca2+ with Mg2+. The amplitude and time course of slow, outward currents were not obviously modified by replacing Ca2+ with Mg2+, having the two described phases. However, in the presence of Cd2+ the first transient phase of the outward current was not detected and only outward currents slowly increasing to a steady level were observed.4. Reliable ICa records were obtained by further blocking K+ outward currents by incubating the muscles in a K+-free TEA+-and Cs+-containing solution prior to experiments. Tubular space clamp was improved by recording ICa from small fibres with 20-30 jsm radius.5. The decay phase of ICa under a maintained depolarization in incubated muscles was fitted by a single exponential. The corresponding rate constant determined between 12 and 24 OC strongly depended on temperature, as expected for a gating process. The values for the activation energy and the corresponding Q10 (calculated for a 10-20 0C transition) were respectively: 17-5 + 1'0 kcal/mole and 2-9 + 0-2 at 0 mV, and 18-0 + 1-5 kcal/mole and 3 0 + 0-3 at -20 mV.6. The activation phase of Ica, analysed following the ma2h Hodgkin-Huxley kinetic model, showed a similar temperature dependence with a Q10 of 3-0 + 0 3. The

No abstract

Patients with anorexia nervosa or bulimia nervosa often have signs of autonomic dysfunction potentially deleterious to the heart. The aim of this study was to ascertain the nonlinear properties of heart rate variability in patients with eating disorders. A group of 33 women with eating disorders (14 anorexia, 19 bulimia) and 19 healthy controls were included in the study. Conventional time- and frequency-domain heart rate variability measurements, along with nonlinear heart rate variability measurements including the short-term fractal scaling exponent alpha and approximate entropy (ApEn) were calculated. Anorexia nervosa patients exhibited decreased values of alpha, while bulimia nervosa patients had decreased values of ApEn. Low-frequency heart rate variability was decreased in patients with anorexia. In conclusion, these results are compatible with the view that a more severe alteration of cardiac autonomic function is present in anorexia than in bulimia.

1. Current and voltage clamp experiments were carried out on frog skeletal muscle fibres. For voltage clamp, the three micro-electrode technique near the fibre end was used. 2. Calcium spikes and currents were recorded in TEA sulphate saline. The addition of 400 mM-glycerol did not appreciably modify them. 3. Muscle fibers were detubulated with the glycerol method. They showed sodium propagating action potentials, with sodium and potassium currents of expected amplitudes. 4. Calcium spikes and currents were reduced or abolished in detubulated muscle fibres. 5. An analysis of fibre capacitance showed a linear correlation between the remaining ICa and the degree of electric discontinuity between the transverse tubular system and the surface membrane. 6. These results indicate that ICa is mainly located in the transverse tubular system. This localization is compatible with some role during mechanical activation.

SUMMARY1. The decay of the Ca2+ current (ICa) during a maintained depolarization was studied in intact twitch skeletal muscle fibres of Rana pipiens and Rana moctezuma with the three-micro-electrode voltage-clamp technique.2. ICa was recorded at 23 TC, after blocking K+ currents, in TEA methanesulphonate saline with 10 mM-Ca2+ made hypertonic by adding 350 mM-sucrose.3. In two-pulse experiments, ICa during the test pulse was reduced to about 80 % (R. pipiens) or 50 % (R. moctezuma) of the control value, without any detectable inward ICa during 7 s conditioning pre-pulses.4. The experimental points of the steady-state inactivation curve (h.) were fitted to hoo = (1 +exp ((Em -Vh)/kh))-, where Em is the membrane potential and with Vh =-33 + 3 mV and kh = 6 +1 mV for R. pipiens, and Vh =-44 + 3 mV and kh = 9-5 + ±10 mV for R. moctezuma.5. The rate constant of decay for inactivated currents (range -8 to -47 mA cm3) and for control currents (range -23 to -62 mA cm-3), was independent of Ica amplitude. The average rate constant of decay at 0 mV was 118 + 002 s-1 (66).6. These results indicate that in intact fibres under hypertonic solution Ica decay can be explained by a voltage-dependent inactivation process and not by depletion of tubular Ca2+. The absence of depletion could be due to a large fractional tubular volume or to the presence of a Ca2+ pump in the tubular system.

No abstract

The diurnal variations and photic regulation of cyclic AMP and melatonin content in golden hamster retina were studied. Both parameters showed significant diurnal variations with maximal values at night. Light exposure during the night inhibited retinal cyclic AMP and melatonin levels, whereas exposure to darkness during the day significantly increased cyclic AMP and melatonin content. Incubation with melatonin of retinas excised at different intervals indicated that the methoxyindole inhibited cyclic AMP accumulation in a time‐dependent manner. The inhibitory effect of melatonin at 2400 h and at noon showed a threshold concentration of 1 and 10 pM, respectively. At 0400 h melatonin did not affect cyclic AMP accumulation. The results indicate a diurnal variability of retinal cyclic AMP and melatonin content in hamsters, mainly influenced by a photic stimulus. Cyclic AMP could be a putative second messenger for melatonin action in golden hamster retina.

No abstract