Submitted on October 23, 2002
Accepted on June 11, 2003
Mild renal hypertension alters run training effects on the frequency response of rat cardiomyocyte mechanics
Bradley M Palmer1*, Eric A Mokelke2, Anne M Thayer2, and Russell L Moore2
1 Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT, USA
2 Department of Kinesiology and Applied Physiology, University of Colorado at Boulder, Boulder, CO, USA
* To whom correspondence should be addressed. E-mail: palmer{at}physiology.med.uvm.edu.
We examined the effects of run training on the frequency dependence of cardiomyocyte mechanics and intracellular calcium ([Ca2+]i) dynamics in rats with mild renal hypertension. Male Fischer 344 rats aged 2-3 months underwent a sham operation (Nt) or stenosis of the left renal artery (Ht), which increased systolic blood pressure 20-30 mmHg. Half of the rats in each group underwent treadmill run training for >16 weeks. Isolated cardiomyocytes were paced at 1.0 and 0.2 Hz in 2 mM external Ca2+ concentration at 29°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 amplified the negative frequency response for the shortening dynamics only in the Nt and not in the Ht. 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.
