Biomedical subjects

Godfrey L Smith

Publications and source records attributed to Godfrey L Smith.

21 records · Page 2Linked to original sources

PubMed2002

Assessment of sarcoplasmic reticulum Ca(2+) flux pathways in cardiomyocytes from rabbits with infarct-induced left-ventricular dysfunction.

The aim of the study was to correlate intracellular Ca(2+) transients with Ca(2+) uptake and efflux characteristics of the sarcoplasmic reticulum (SR) in ventricular myocytes isolated from rabbits with left-ventricular dysfunction (LVD). Chronic (8 weeks) ligation of a coronary artery caused marked LVD in rabbits. Measurements of intracellular [Ca(2+)] were made using Fura-2 on intact, single, left-ventricular myocytes. SR Ca(2+) flux rates associated with sarco-endoplasmic reticulum Ca(2+) ATPase type 2 (SERCA2)-mediated uptake, ryanodine receptor type 2 (RyR2)-mediated Ca(2+) efflux and background SR Ca(2+) leak were measured in suspensions of permeabilised myocytes. Measurements on single, permeabilised myocytes were used to assess the steady-state Ca(2+) content of the SR and the characteristics of spontaneous SR Ca(2+) release. Peak systolic [Ca(2+)] was significantly lower; time-to-peak and Ca(2+) transient duration were significantly longer in LVD myocytes. SERCA2-mediated Ca(2+) uptake was reduced to approximately 50% in myocytes from the LVD group. Ruthenium red (RuR)-sensitive Ca(2+) efflux (mediated by the RyR2) was also reduced in the LVD group by approximately 50%, as was the remaining (RuR-insensitive) background Ca(2+) leak. Measurements from single, permeabilised myocytes showed a lower steady-state SR Ca(2+) content. The frequency and amplitude of spontaneous SR Ca(2+) release from LVD hearts was also reduced. Partial inhibition of SERCA2 by thapsigargin depressed both the amplitude and the frequency of spontaneous release. Partial inhibition of RyR2-mediated-Ca(2+) efflux with tetracaine enhanced spontaneous Ca(2+) release amplitude and decreased frequency. Increased background Ca(2+) leak with ionomycin decreased the frequency of spontaneous release. It is concluded that partial inhibition of SERCA2 mimics some aspects of altered SR function in LVD, but reduced RyR2 function cannot explain the other functional alterations observed. Reduced background Ca(2+) leak from the SR may compensate partly for the reduced Ca(2+) uptake capacity of the SR in the LVD group.

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PubMed2002

Ultra-low-volume, real-time measurements of lactate from the single heart cell using microsystems technology.

The fabrication of microelectrodes integrated within ultra-low-volume microtiter chambers for the amperometric determination of metabolites continues to be of interest in the subject of single-cell and high-throughput screening. The microsystem described in this paper consists of a two-microelectrode sensor with a microfluidic dispensation technology, which is able to deliver both very low titers (6.5 pL) and single heart cells into a low-volume microphotoelectrochemical cell. Devices were fabricated using photolithography and liftoff giving reproducible sensors integrated within high aspect ratio titer chambers (with a volume of 360 pL), made of the photoepoxy SU8. In this paper, the determination of lactate was optimized using an enzyme-linked assay based upon lactate oxidase, involving the amperometric determination of hydrogen peroxide at +640 mV versus an internal Ag/AgCl pseudoreference. The microsystem (including the microfluidic dispensers and structures as well as the microsensor) was subsequently used to measure the lactate content of single heart cells. Dynamic electrochemical measurements of lactate during cell permeabilization are presented. We also show the use of respiratory uncouplers to simulate ischemia in the single myocyte and show that, as expected, the rate of lactate production from the hypoxic heart cell is greater than that within the normoxic healthy myocyte.

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PubMed2002

Aerobic exercise reduces cardiomyocyte hypertrophy and increases contractility, Ca2+ sensitivity and SERCA-2 in rat after myocardial infarction.

OBJECTIVE: Although it is generally accepted that endurance training improves cardiac function after myocardial infarction the sub-cellular mechanisms are uncertain. The present study reports the effects of aerobic endurance training on myocardial mass, myocyte dimensions, contractile function, Ca2+ handling, and myofilament responsiveness to Ca2+ in cardiomyocytes from healthy and failing rat hearts. METHODS: Adult female Sprague-Dawley rats ran on a treadmill 1.5 h/day, 5 days a week for 8 weeks. Exercise intervals alternated between 8 min at 85-90% of V(O(2max)) and 2 min at 50-60%. Training started 4 weeks after ligation of the left coronary artery (TR-INF, n=11) or sham operation (TR-SHAM, n=6). Sedentary animals (SED-SHAM, n=6; SED-INF, n=13) were controls. RESULTS: After 6 weeks V(O(2max)) in TR-INF and TR-SHAM leveled off 65% above sedentary controls. In TR-SHAM, left and right ventricle weights were approximately 25% higher than in SED-SHAM, myocytes were approximately 13% longer; width remained unchanged. At physiological stimulation frequencies, relative myocyte shortening was markedly higher whereas peak systolic [Ca2+] and t(1/2) of Ca2+ transient decay were 10-20% lower, indicating higher Ca2+ sensitivity in cardiomyocytes from trained rats, compared to respective controls. In TR-INF the left and right ventricular weights, and myocyte length and width were 15, 23, 12, and 20% less than in SED-INF. Endurance training significantly increased the myocardial SR Ca2+ pump (SERCA-2) and sarcolemmal Na+-Ca2+-exchanger (NCX) protein levels to the extent that TR-INF did not differ from SED-SHAM. CONCLUSION: This is the first study to show that aerobic endurance training attenuates the ventricular and cellular hypertrophy in failing hearts. Furthermore, training consistently restores contractile function, intracellular Ca2+ handling, and Ca2+-sensitivity in cardiomyocytes from rats with myocardial infarction.

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