To study antibiotic efficacy, 29 patients with leptospirosis were treated in a randomized, double-blinded fashion with doxycycline, 100 mg orally twice a day, or placebo. Therapy was given for 7 days in a hospital, and patients were followed for 3 weeks afterwards. Duration of illness before therapy and severity of illness were the same in both groups. Doxycycline reduced the duration of illness by 2 days and favorably affected fever, malaise, headache, and myalgias. Treatment prevented leptospiruria and had no adverse effects. Doxycycline is effective in therapy for patients with leptospirosis.

1. The intracellular sodium activity (aN^), contraction and membrane current were recorded simultaneously in voltage-clamped guinea-pig ventricular myocytes. 2. Increasing the frequency (from 0 5 to 3 Hz) of voltage clamp pulses to 0 mV from a holding potential of -80 mV led to an increase in both a'a and contraction. The ratedependent increase in contraction was reduced by 25 ,UM tetrodotoxin (TTX) and abolished with a holding potential of -40 mV. There was no rate-dependent rise in a'Na with a holding potential of -40 mV. These results suggest an important role for a' a and in particular Na+ influx via Na+ channels during rate-dependent changes in contraction. 3. After an increase in frequency from 0'5 to 3 Hz, membrane current at the end of voltage clamp pulses became progressively more outward and the tail current upon repolarization became progressively more inward compared with those recorded at 0 5 Hz. ITTX reduced the magnitude of both the outward and inward rate-dependent shifts of current. 4. The addition of extracellular CsCl blocked the inward rectifier potassium current (IK 1) and the delayed rectifier (IK), but did not change the rate-dependent shift in current. 5. The difference between current-voltage relationships at 0 5 and 3 Hz showed that the rate-dependent outward shift of current at the end of voltage clamp pulses was small at potentials negative to -20 mV, was larger at more positive potentials and was reduced by TTX at most potentials. The TTX-sensitive component reversed at -47 mV.6. These results are consistent with a net increase in outward Na+-Ca2+ exchange current during a voltage clamp pulse in response to the rise of aia. The increase in outward current (resulting from either enhanced Ca2+ influx or reduced Ca2+ efflux) will augment the Ca2+ load of the cell and contribute to the rate-dependent increase in contraction.

No abstract

The properties of left ventricular cardiac myocytes vary transmurally. This may be related to the gradients of stress and strain experienced in vivo across the ventricular wall. We tested the hypothesis that within the rat left ventricle there are transmural differences in the expression of genes for proteins that are involved in mechanosensitive pathways and in associated physiological responses. Real time reverse transcription polymerase chain reaction was used to measure messenger RNA (mRNA) levels of selected targets in sub-epicardial (EPI) and subendocardial (ENDO) myocardium. Carbon fibres were attached to single myocytes to stretch them and to record contractility. We observed that the slow positive inotropic response to stretch was not different between EPI and ENDO myocytes and consistent with this, that the mRNA expression of two proteins implicated in the slow response, non-specific cationic mechanosensitive channels (TRPC-1) and Na/H exchanger, were not different. However, mRNA levels of other targets, e.g. the mechanosensitive K + channel TREK-1, Brain Natriuretic Peptide and Endothelin-1 receptor B, were significantly greater in ENDO than EPI. No targets had significantly greater mRNA levels in EPI than ENDO. On the basis of these findings, we suggest that the response of the ventricle to stretch will depend upon both the regional differences in stimuli and the relative expression of the mechanosensitive targets and that generally, stretch sensitivity is predicted to be greater in ENDO.

We have described the concentration-dependent inotropic effects of halothane, isoflurane and sevoflurane on rat ventricular cells and investigated the role of the sarcoplasmic reticulum (SR) in these inotropic actions. Single ventricular myocytes, isolated from rat hearts, were stimulated electrically at 1 Hz and contractions recorded optically. Cells were exposed to a range of concentrations of halothane, isoflurane or sevoflurane for a period of 1 min to determine the concentration-dependency of their inotropic actions. For each anaesthetic, the peak negative inotropic action was determined early during an exposure, and sustained negative inotropic action was measured at steady-state just before wash-off. In some experiments, cells were equilibrated with ryanodine 1 mumol litre-1 to investigate the role of the SR in these intropic effects. Halothane caused a concentration-dependent initial increase in contractions (to mean 130 (SEM 28)% at 10 mmol litre-1) followed by rapid onset of a negative inotropic effect (K0.5 0.34 mmol litre-1 for peak effect; K0.5 0.46 mmol litre-1 for sustained effect). Exposure to isoflurane induced a small potentiation of contractions in some cells, followed by a concentration-dependent decrease in contraction in all cells (K0.5 0.85 mmol litre-1 for peak effect; K0.5 1.92 mmol litre-1 for sustained effect); contractions recovered partially during a 1-min exposure. On wash-off, contractions were increased transiently above control. Sevoflurane caused a large initial decrease in contraction which then returned rapidly towards control (K0.5 0.2 mmol litre-1 for peak effect; K0.5 2.57 mmol litre-1 for sustained effect). In common with isoflurane, removal of sevoflurane caused a transient increase in contractions above control. After exposure to ryanodine, the positive inotropic effects of halothane and isoflurane did not occur, and recovery of contractions during exposure to isoflurane and sevoflurane was abolished as was the transient increase in contractions seen on wash-off, indicating that these effects were mediated via the SR. Halothane had the most potent sustained negative inotropic effect but there was little difference between the negative inotropic effects of isoflurane and sevoflurane at clinically relevant concentrations. At higher concentrations, sevoflurane caused a less potent negative inotropic effect than isoflurane. The SR plays a major role in the effects of all three anaesthetics. One possible mechanism underlying the initial potentiation of contraction by halothane (and isoflurane) may be sensitization of the Ca(2+)-induced Ca(2+)-release process of the SR.

SUMMARYWe have investigated the effect of temperature upon the rate-dependent decrease in the L-type Ca2+ current (ica) in isolated rat ventricular myocytes. Increasing the rate of stimulation from 0.5 to 3.0 Hz for 30 s induced a reversible decrease in ica which was temperature dependent.Compared to control (0-5 Hz), the first beat at 3 Hz was decreased by 38 + 7 % at 22°C and by 9 + 1 % at 37°C (mean + S.E.M., n = 5, P < 0.05) and, after 30 s of 3 Hz stimulation, iCa was reduced by a further 26 + 4 and 21 + 2 % at 22 and 37°C, respectively. The magnitude of this secondary decline was not significantly different at the two temperatures (P =0.29). Corroboratory results were obtained from cell-attached patches which also illustrated that the ratedependent decrease in ica resulted from a reduction of open channel probability. Paired pulse experiments showed that the greater initial rate-dependent decrease in iCa at 22°C occurred as a result of slower recovery from fast inactivation processes at 22 than at 37 'C. Recovery of the channel from fast inactivation was very temperature sensitive with a Q10 of 5.6. In contrast, the secondary, progressive decrease in iCa, which results from incomplete recovery from ultra-slow voltage-dependent inactivation, was similar at the two temperatures and appears to be much less temperature dependent.

In contrast to a previous report, we could find no evidence of amelioration of the negative inotropic effect of halothane in myocytes from the STZ-induced diabetic rat. Contractility, the cytosolic Ca(2+) transient, SR Ca(2+) content and myofilament Ca(2+) sensitivity were qualitatively similar in control and STZ myocytes and were all depressed to the same extent by halothane.

SUMMARYVentricular myocytes, isolated from the guinea-pig, were stimulated to contract by 100 ms long voltage clamp pulses from -80 to 0 mV at 0-5 and 3 Hz. An increase in frequency from 0-5 to 3 Hz led to a positive inotropic effect. Contraction-voltage relationships (CVR) were determined at each frequency. The CVR at 0.5 Hz was bell shaped and peaked between 0 and +20 mV, displaying a voltage dependence similar to the L-type Ca2+ current (ICa). At 3 Hz, contractions continued to increase at positive voltages, giving a more sigmoidal CVR. At 0-5 Hz, TTX reduced the size of steady-state contractions to 91 + 2 % of control values, but had no effect on the shape of the CVR. At 3 Hz, TTX significantly reduced (P < 0.05) the magnitude of contractions at positive voltages (> +20 mV) but had no significant effect on contractions at voltages negative to 0 mV. These data illustrate that intracellular sodium activity (a' a) and, in particular, Na+ entry due to the sodium current (INaJ are important in determining the voltage dependence of contraction at positive voltages. Thapsigargin (2-5 ,uM), a blocker of the sarcoplasmic reticulum (SR) Ca2+-ATPase, reduced the size of steady-state contractions at 0 mV to 65 ± 7 % at 0-5 Hz. Increasing frequency to 3 Hz abolished the positive inotropy seen under control conditions. With thapsigargin present, contractions at 0-5 Hz were reduced at all potentials and the CVR was bell shaped. At 3 Hz the CVR was sigmoidal in shape. Contractions were significantly inhibited by thapsigargin at all potentials, but most significantly at more positive potentials ( > +20 mV). These data show that, at normal body temperature, the shape of the CVR of guinea-pig ventricular myocytes changes with stimulation rate. Due to the voltage dependence of ICa, contractions evoked at positive voltages at 3 Hz must be supported by other mechanisms. The sensitivity of such contractions to TTX and thapsigargin suggests the involvement of both a Na+-dependent process and the SR. One possibility is that when a'a and the Ca2+ content of the SR are raised at higher stimulation rates, enhanced Ca2+ entry via reverse Na+-Ca2+ exchange leads to a direct activation of the myofilaments and, to a lesser extent, the release of Ca2+ from the SR.