Bartter's syndrome (BS) is characterized by arterial normohypotension
despite biochemical and hormonal abnormalities generally associated wi
th hypertension. An abnormal intracellular calcium homeostasis due to
a reduced capacity to increase intracellular calcium has been demonstr
ated by us in BS and proposed as the main pathophysiological factor of
the vascular hyporeactivity in BS. The present study was designed to
assess whether this altered intracellular calcium homeostasis could al
so impair contractile recruitment at the myocyte level. Left-ventricul
ar function of patients with BS and normal subjects (C) were studied b
y quantitative 2-D echocardiography at rest and by postextrasystolic p
otentiation (PESP), an inotropic stimulus able to recruit the maximal
contractile reserve. A group of patients with hypokalemia other than B
S (PB) was also included in the study to evaluate the effect of hypoka
lemia on myocardial contractile recruitment. Baseline left-ventricular
end-diastolic volume (EDV) and ejection fraction (EF) did not differ
in the 3 groups: EDV: 62 +/- 6 vs. 64 +/- 9 and 60 +/- 12 ml/m(2); EF:
64 +/- 9 vs. 67 +/- 8 and 64 +/- 8%. PESP determines an increase of E
F in C and PB: 82 +/- 5%, p < 0.01 and 76 +/- 6%, p < 0.01, while in B
S it is unchanged: 69 +/- 9% and is reduced in comparison with the inc
rement of myocardial function shown by C and PB (p < 0.01). This study
is the first demonstration in BS of a depressed inotropic recruitment
causing an exercise-induced left-ventricular dysfunction likely due t
o an abnormal intracellular calcium homeostasis in the myocytes.