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|Type:||Artigo de periódico|
|Title:||Osmolality- and Na+-dependent effects of hyperosmotic NaCl solution on contractile activity and Ca2+ cycling in rat ventricular myocytes|
|Abstract:||Hypertonic NaCl solutions have been used for small-volume resuscitation from hypovolemic shock. We sought to identify osmolality- and Na+-dependent components of the effects of the hyperosmotic NaCl solution (85 mOsm/kg increment) on contraction and cytosolic Ca2+ concentration ([Ca2+](i)) in isolated rat ventricular myocytes. The biphasic change in contraction and Ca2+ transient amplitude (decrease followed by recovery) was accompanied by qualitatively similar changes in sarcoplasmic reticulum (SR) Ca2+ content and fractional release and was mimicked by isosmotic, equimolar increase in extracellular [Na+] ([Na+](o)). Raising osmolality with sucrose, however, augmented systolic [Ca2+](i) monotonically without change in SR parameters and markedly decreased contraction amplitude and diastolic cell length. Functional SR inhibition with thapsigargin abolished hyperosmolality effects on [Ca2+](i). After 15-min perfusion, both hyperosmotic solutions slowed mechanical relaxation during twitches and [Ca2+](i) decline during caffeine-evoked transients, raised diastolic and systolic [Ca2+](i), and depressed systolic contractile activity. These effects were greater with sucrose solution, and were not observed after isosmotic [Na+](o) increase. We conclude that under the present experimental conditions, transmembrane Na+ redistribution apparently plays an important role in determining changes in SR Ca2+ mobilization, which markedly affect contractile response to hyperosmotic NaCl solutions and attenuate the osmotically induced depression of contractile activity.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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