Mild renal hypertension alters run training effects on the frequency response of rat cardiomyocyte mechanics

We examined the effects of run training on the frequency dependence of cardiomyocyte mechanics and intracellular calcium concentration ([Ca2+]i) dynamics in rats with mild renal hypertension. Male Fischer 344 rats aged 2-3 mo underwent a sham operation or stenosis of the left renal artery, which increased systolic blood pressure 20-30 mmHg. Half of the rats in each group underwent treadmill run training for >16 wk. Isolated cardiomyocytes were paced at 1.0 and 0.2 Hz in 2 mM external Ca2+ concentration at 29 degrees C. Under these conditions, negative frequency responses, i.e., decreased value with increased frequency, were recorded for peak shortening, shortening velocity, and the integral of the [Ca2+]i transient in both groups. Run training amplified the negative frequency response for the integral of the [Ca2+]i transient in both groups, but it amplified the negative frequency response for the shortening dynamics only in the normotensive sham-operated and not in the hypertensive rats. These results, as well as others for relaxation parameters, suggest that renal hypertension altered the effects of run training on the frequency response for cardiomyocyte contractile apparatus and/or passive mechanical properties, which respond to [Ca2+]i.