[Effect of metoprolol on ventricular relaxation in experimental myocardial infarction]. / Efecto del metoprolol sobre la relajación ventricular en el infarto del miocardio experimental.

During the initial phases of myocardial infarction the relaxation ventricular time increases. To assess the effect of metoprolol, a beta-blocker agent, on constant T, an index derived from left ventricular pressure during the isovolumic relaxation phase, 12 mongrel dogs underwent surgical ligation of the anterior descending coronary artery. Constant T, diastolic ventricular pressure, heart rate and mean arterial pressure were measured at control and after 15, 30, 60, 120 and 180 minutes after arterial occlusion. Six dogs were used as controls while the other six received 35 mg/kg/min of methoprolol, infused during 5 minutes. Untreated dogs had longer T times, higher ventricular filling pressures and hypotension at the end of the study in comparison with the treated does, who maintained diastolic function and did not show important changes of arterial pressure. The beta-blocker decreased the abnormality of relaxation time and preserved ventricular filling and systemic pressures in this model of experimental infarction.

B-subunit of phosphate-specific transporter from Mycobacterium tuberculosis is a thermostable ATPase.

The B-subunit of phosphate-specific transporter (PstB) is an ABC protein. pstB was polymerase chain reaction-amplified from Mycobacterium tuberculosis and overexpressed in Escherichia coli. The overexpressed protein was found to be in inclusion bodies. The protein was solubilized using 1.5% N-lauroylsarcosine and was purified by gel permeation chromatography. The molecular mass of the protein was approximately 31 kDa. The eluted protein showed ATP-binding ability and exhibited ATPase activity. Among different nucleotide triphosphates, ATP was found to be the preferred substrate for M. tuberculosis PstB-ATPase. The study of the kinetics of ATP hydrolysis yielded K(m) of approximately 72 microm and V(max) of approximately 0.12 micromol/min/mg of protein. Divalent cation like manganese was inhibitory to the ATPase activity. Magnesium or calcium, on the other hand, had no influence on the functionality of the enzyme. The classical ATPase inhibitors like sodium azide, sodium vanadate, and N-ethylmaleimide were without any effect but an ATP analogue, 5'-p-fluorosulfonylbenzoyl adenosine, inhibited the ATPase function of the recombinant protein with a K(i) of approximately 0.40 mm. Furthermore, there was hardly any ATP hydrolyzing ability of the PstB as a result of mutation of the conserved aspartic acid residue to lysine in the Walker motif B, confirming the recombinant protein is an ATPase. Interestingly, analysis of the recombinant PstB revealed that it is a thermostable ATPase; thus, our results highlight for the first time the presence of such an enzyme in any mesophilic bacteria.