Phospholamban deficiency does not compromise exercise capacity

Deficiency of phospholamban (PLB) results in enhancement of basal murine ca rdiac function and an attenuated response to P-adrenergic stimulation. To d etermine whether the absence of PLB also reduces the reserve capacity of th e murine cardiovascular system to respond to stress, we evaluated the heart rate (HR), blood pressure, and metabolic responses of PLB-deficient (PLB-/ -) mice to graded treadmill exercise (GTE). PLB-/- mice were hypertensive a t rest (125 +/- 19 vs. 109 +/- 16 mmHg, P < 0.05) but had normal tachycardi c and hypotensive responses to isoproterenol. The HR response to GTE was no rmal; however, the hypertension in PLB-/- mice normalized at peak exercise. Their exercise capacities, as measured by duration of exercise and peak ox ygen consumption ((V) over dot O-2), were normal. The oxygen pulse ((V) ove r dot O-2/HR) curve was also normal in PLB-/- mice, suggesting an ability t o appropriately increase stroke volume and oxygen extraction during GTE, de spite an inability to increase beta-adrenergically stimulated cardiac contr actility. Thus deficiency of PLB, although resulting in diminished beta-adr energic inotropic reserve, does not compromise cardiac performance during e xercise.