Renal hypertension prevents run training modification of cardiomyocyte diastolic Ca2+regulation in male rats

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Abstract
The combined effects of endurance run training and renal hypertension on cytosolic Ca2+concentration ([Ca2+]c) dynamics and Na+-dependent Ca2+regulation in rat left ventricular cardiomyocytes were examined. Male Fischer 344 rats underwent stenosis of the left renal artery [hypertensive (Ht), n = 18] or a sham operation [normotensive (Nt), n = 20]. One-half of the rats from each group were treadmill trained for >16 wk. Cardiomyocyte fura 2 fluorescence ratio transients were recorded for 7 min during electrical pacing at 0.5 Hz, 2 mM extracellular Ca2+concentration, and 29°C. The rate of [Ca2+]cdecline was not changed by run training in the Nt group but was reduced in the Ht group. At 7 min, cardiomyocytes were exposed to 10 mM caffeine in the absence of Na+and Ca2+, which triggered sarcoplasmic reticular Ca2+release and suppressed Ca2+efflux via Na+/Ca2+exchanger. External Na+was then added, and Na+-dependent Ca2+efflux rate was recorded. Treadmill training significantly enhanced Na+-dependent Ca2+efflux rate under these conditions in the Nt group but not in the Ht group. These data provide evidence that renal hypertension prevents the normal run training-induced modifications in diastolic [Ca2+]cregulation mechanisms, including Na+/Ca2+exchanger.