John A. Spratt

Rates of growth of human neoplasms: Part II

Part I of this study [Spratt JS, Meyer JS, Spratt JA: J Surg Oncol 60:137–146, 1995] reviewed the early reports of investigators, predominantly mathematical biologists and statisticians considering the mathematical laws that would describe the growth of a neoplasm. Included were cytokinetic measurements of the mitotic index, thymidine labeling index, bromodeoxyurine labeling index, and the relation of these indices to the potential tumor volume doubling time. The actual doubling time of benign and malignant colonic neoplasms were reported.

Salbutamol changes the molecular and mechanical properties of canine skeletal muscle.

1. Salbutamol, a beta 2‐agonist, increased the weight of the canine latissimus dorsi muscle. It also increased fusion frequency, and decreased time‐to‐peak tension, half‐relaxation time, and total contraction time. These changes in twitch times and fusion frequency were associated with changes in the levels of proteins expressed in slow‐ and fast‐twitch fibres. Salbutamol decreased the levels of the slow‐twitch cardiac isoform of sarco‐/endoplasmic reticulum Ca(2+)‐ATPase (SERCA2a) and phospholamban proteins, and increased the level of the fast‐twitch isoform of sarco‐/endoplasmic reticulum Ca(2+)‐ATPase (SERCA1a). 2. Changes in the levels of SERCA proteins, particularly SERCA1a, could account for most of the increases in calcium uptake rate observed in homogenates of muscles from the salbutamol‐treated animals and could partially account for the changes in half‐relaxation rates and other twitch times. 3. Changes in the levels of SERCA1a, SERCA2a and phospholamban protein did not always follow changes in the levels of their corresponding mRNAs. Divergence depended upon the SERCA isoform and muscle. The muscles studied were latissimus dorsi and vastus intermedius. 4. Salbutamol did not change the level of myosin heavy chain (HC)‐I isoforms in either muscle, suggesting that it did not increase the proportion of slow‐twitch fibres in these muscles. It did increase the level of HC‐IIx and decrease the level of HC‐IIa isoforms in the latissimus dorsi. Salbutamol did not produce these effects in the vastus intermedius. It is of particular interest that salbutamol changed the relative levels of SERCA proteins in the latissimus dorsi muscle without producing significant change in the level of HC‐I isoform.

FAST- AND SLOW-TWITCH ISOFORMS (SERCA1 AND SERCA2A) OF SARCOPLASMIC RETICULUM CA-ATPASE ARE EXPRESSED SIMULTANEOUSLY IN CHRONICALLY STIMULATED MUSCLE FIBERS

Abstract Using an immunohistochemical double-labeling technique, we observed that different isoforms of sarcoplasmic reticulum Ca-ATPase are co-expressed in single fibers of canine fast-twitch skeletal muscles stimulated chronically at low frequency. By 7 days of neuromuscular stimulation, the population of hybrid fibers expressing both SERCA1 and SERCA2a [fast- and slow-twitch isoforms of sarco(endo)plasmic reticulum Ca2+-ATPase] had increased from 1.5% to 9.2% of fibers. By 14 days of stimulation 90% of the pure fast-twitch fibers (expressing only SERCA1) were replaced by hybrid fibers. An additional 28 days of stimulation caused all fast-twitch fibers to express SERCA2a at the same level as found in nonstimulated slow-twitch fibers (expressing only SERCA2a). At this time, one-half of the previously hybrid fibers had become pure slow-twitch fibers. The remaining one-half of the hybrid fibers expressed SERCA1 at a very low level. Extending stimulation to 70 days did not further change the percentage of fibers that were slow-twitch or hybrid. Immunoblot studies at the whole-muscle level confirmed that changes in SERCA expression at 42 days of neuromuscular stimulation were complete. Immunohistochemical analysis of longitudinal sections of muscle showed that the changes in SERCA protein were uniform along the length of the muscle fiber, indicating that nuclei along its length responded equally to chronic stimulation.

Correlations between MyoD, myogenin, SERCA1, SERCA2 and phospholamban transcripts during transformation of type-II to type-I skeletal muscle fibers.

Abstract Canine latissimus dorsi, composed predominantly of fast-twitch muscle fibers, were subjected to chronic 1 Hz neuromuscular stimulation for periods up to 42 days to induce changes in gene expression. This produced down regulation of SERCA1 (fast-twitch isoform of sarco(endo)plasmic reticulum Ca2+-ATPase), a gene product of fast-twitch muscle, and up regulation of SERCA2 (slow-twitch isoform of sarco(endo)plasmic reticulum Ca2+-ATPase) and phospholamban, products of genes expressed by slow-twitch muscles. To assess the involvement of MyoD and myogenin in the regulation of the expression of these genes their levels were measured during the stimulation period. The prompt, at 7 days, fall in SERCA1 mRNA preceded the fall in MyoD by about 7 days, suggesting that the decline in MyoD was not causally related to the decline in SERCA1. The prompt rise in SERCA2 mRNA at 7 days preceded the rise in myogenin by 14 days. The rise in myogenin at 21 days did correlate with the similar rise in phospholamban mRNA.

Induction of molecular and mechanical transformations in canine skeletal muscle by chronic neuromuscular stimulation

The canine latissimus dorsi was stimulated at 1 Hz via the thoracodorsal nerve for 70 days. Seven days of muscle stimulation caused muscle mass, fibre cross-sectional areas, and tetanic tensions to decrease. Fourteen days of stimulation produced marked decreasesin Ca2+-uptake rates in a membrane fraction containing sarcoplasmic reticulum. At this time there was a decline infusion frequency, but no statistically significant changes in time-to-peak tension, total contraction times, or half-relaxation times. With 42 days of stimulation a switch from the fast-twitch to the slow-twitch phenotype was indicated by elevations in the levels of expression of the slow-twitch isoform of sarco(endo)plasmic reticulum Ca2+-ATPase and myosin heavy chain-I, and increases in half-relaxation times, total contraction times and time-to-peak tensions. Decreases in muscle shortening velocity correlated negatively with increases in myosin heavy chain-I levels. Up-regulation of the slow-twitch isoform of sarco(endo)plasmic reticulum Ca2+-ATPase protein positively correlated with increases in half-relaxation times. The changes in the slow-twitch isoform of sarco(endo)plasmic reticulum Ca2+-ATPase and myosin heavy chain-I levels indicated coordinate expression of these two proteins in chronically stimulated muscles

Clinical experience with nonthoracotomy cardioverter defibrillators

A new generation of defibrillators has been introduced that do not require a thoracotomy. The purpose of this report was to examine 100 consecutive nonthoracotomy implantations at our institution and compare them with a series of 102 patients undergoing thoracotomy implantations by the same surgeon over a 4-year period between August 1989 and September 1994. The two groups were comparable for age, sex, comorbidity, cardiac disease status, ejection fraction, and electrophysiologic presentation. Nonthoracotomy systems were implanted successfully in 94% of patients. Patients undergoing a nonthoracotomy implantation had significantly shorter intensive care unit (1.7 +/- 1.7 versus 3.3 +/- 3.9 days; p < 0.005) and postoperative stays (5.0 +/- 2.8 versus 9.5 +/- 5.6 days; p < 0.001) than patients undergoing a thoracotomy approach. This was due to a significant decrease in the incidence of postoperative complications from 29% in the thoracotomy group to 11% in the nonthoracotomy group (p < 0.001). There was no significant difference in overall mortality rates. Nonthoracotomy systems are implantable in the majority of patients and are associated with less morbidity and shorter hospital stays than traditional thoracotomy approaches.

Transcription rates of SERCA and phospholamban genes change in response to chronic stimulation of skeletal muscle.

Chronic low frequency stimulation of predominantly fast-twitch skeletal muscles decrease the levels of SERCA1 (fast-twitch sarco(endo)plasmic reticulum Ca2+-ATPase) mRNA, and increase the levels of SERCA2 (slow-twitch sarco(endo)plasmic reticulum Ca2+-ATPase) and phospholamban mRNAs. To assess the role of transcription in these changes in mRNA levels, nuclei were isolated from chronically stimulated canine latissimus dorsi muscles and transcription rates were estimated by nuclear run-on assays. Decreases in the rates of SERCA1 gene transcription matched the fall in its mRNA level and increases in the rates of SERCA2 and phospholamban gene transcription matched the increases in their mRNAs.

Salbutamol and chronic low‐frequency stimulation of canine skeletal muscle.

1. The effect of simultaneous application of chronic muscle stimulation and salbutamol on the expression of mRNAs and proteins normally expressed by fast‐ or slow‐twitch fibres was followed and the effects of changes in protein expression on mechanical performance were evaluated. Chronic low‐frequency stimulation increased the myosin heavy chain (HC)‐I level in the canine latissimus dorsi muscle and simultaneous administration of salbutamol partially blocked this change. Associated with the increase in HC‐I level was a decrease in the velocity of shortening at zero load, VMAX. The change in VMAX was partially blocked by salbutamol. 2. Chronic low‐frequency stimulation increased the levels of slow‐twitch cardiac isoform sarco‐/endoplasmic reticulum Ca(2+)‐ATPase (SERCA2a) and phospholamban mRNA, and SERCA2a and phospholamban protein expression. These changes were associated with an increase in time‐to‐peak tension and a decrease in fusion frequency. Simultaneous administration of salbutamol blocked these changes in protein expression and muscle mechanics. Chronic stimulation of latissimus dorsi decreased the levels of the fast‐twitch isoform of sarco‐/endoplasmic reticulum Ca(2+)‐ATPase (SERCA1a) and increased SERCA2a protein expression and decreased calcium uptake rate by muscle homogenates. These changes were blocked by salbutamol. 3. The loss of latissimus dorsi muscle weight by chronic stimulation was partially blocked by salbutamol.

Improved identification of posterior left ventricular pseudoaneurysms by transesophageal echocardiography

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The β2-agonist salbutamol affects the expression of phospholamban and both isoforms of SERCA in canine skeletal muscle and blocks changes in these induced by neuromuscular stimulation

Abstract Chronic administration of salbutamol induced expression of hybrid fibers in canine skeletal muscles. Fast-twitch fibers expressed SERCA2a (the slow-twitch isoform of sarcoplasmic reticulum Ca2+-ATPase) and slow-twitch fibers expressed SERCA1 (the fast-twitch isoform of the Ca2+-ATPase). The proportion of fibers that became hybrid increased from a small percentage in the control muscles to 30% in the predominantly fast-twitch latissimus dorsi and to 45% in the predominantly slow-twitch vastus intermedius. In contrast to this response by the SERCA genes the phospholamban gene response was muscle specific. The fraction of fibers that expressed phospholamban decreased slightly in the latissimus dorsi while increasing moderately in the vastus intermedius. The effects of chronic neurostimulation of the latissimus dorsi on SERCA1, SERCA2a and phospholamban levels were mostly blocked by salbutamol. While 100% of fibers from neurostimulated muscles expressed phospholamban, only 51% of the fibers from the neurostimulated and salbutamol-treated muscles expressed it. In the neurostimulated muscle, very few muscle fibers expressed SERCA1a while 61% of the fibers that received salbutamol expressed it, albeit as hybrid fibers. The levels of SERCA2a in response to these interventions were just the opposite. In the neurostimulated muscle 37.5% of fibers were hybrid and 62.5% expressed SERCA2a only. With co-administration of neurostimulation and salbutamol, 61.3% of fibers were hybrid and 38.7% expressed SERCA2a only.