title: Enhanced acidotic myocardial Ca2+ responsiveness with training in hypertension.
abstract: OBJECTIVE
  We tested how hypertension-induced compensated hypertrophy, both alone and coupled with exercise training, affects left ventricular (LV) Ca(2+) responsiveness during acidosis.
  
  
  METHODS
  Four-month-old female, spontaneously hypertensive rats (SHR) (N = 23) were assigned to a sedentary (SHR-SED) or treadmill-trained (SHR-TRD) group (60% VO(2peak), 5 d.wk(-1), 6 months), while Wistar-Kyoto rats (WKY) (N = 12) served as normotensive controls. LV performance was established in response to supraphysiologic Ca(2+) infusion (4 mmol.L(-1)) alone and concomitant with isoproterenol (ISO) (1 x 10 mol.L(-1)) at pH 7.4 and 6.8.
  
  
  RESULTS
  HR, rate-pressure product (RPP), and blood pressure were greater in SHR than in WKY (P < 0.05). HR and RPP were attenuated with training. Heart weight and LV anterior wall thickness (diastole) were increased in SHR relative to WKY (P < 0.05) and augmented with training. ISO + 4 mmol.L(-1) [Ca]o resulted in similar LV performance at pH 7.4. At pH 6.8, LV developed pressure was greater in both SHR groups (P < 0.05) versus WKY rats and a twofold increase in the [Ca(2+)]o rescued LV performance to the greatest extent in SHR-TRD. During acidosis, the added stimulus of ISO coupled with elevated [Ca(2+)](o) improved WKY LV performance to near baseline (P < 0.05). Neither elevated [Ca(2+)](o) nor ISO was effective in rescuing LV performance in SHR-SED during acidosis. Phospholamban phosphorylation at Ser(16) and Thr(17) residues were positively correlated with LV functional recovery. Regulatory proteins such as the Na(+)/H(+) exchanger, Na(+)/Ca(2+) exchanger, and the L-type Ca(+) channel were not correlated with LV function.
  
  
  CONCLUSIONS
  Myocardial tolerance to acidosis is improved during the adaptive phase of compensatory hypertrophy. Furthermore, exercise training in SHR induced a myocardial phenotype that preserved Ca(2+) responsiveness during acidosis.
authors: Department of Kinesiology, Temple University, Philadelphia, PA 19122, USA.
authors: Brian F
authors: BF
authors: Renna
authors: Hajime
authors: H
authors: Kubo
authors: Scott M
authors: SM
authors: MacDonnell
authors: Deborah L
authors: DL
authors: Crabbe
authors: Patricia O
authors: PO
authors: Reger
authors: Steven R
authors: SR
authors: Houser
authors: Joseph R
authors: JR
authors: Libonati