Exercise-induced change in β-adrenergic receptor number in lymphocytes from trained and untrained men

Abstract

This study was undertaken to clarify whether β-adrenergic receptor (β-AR) translocation from intracellular sites to the cell surface contributes to an increase in the number of β-AR in lymphocytes from trained and untrained men after exercise. Nine trained and 9 untrained subjects performed exercise on a bicycle ergometer until exhaustion. The number of β-AR in the cell surface (β-AR(surface)) and intracellular sites (β-AR(intra)) was determined at rest and after maximal exercise by measuring the binding of the radioligand 125I-iodocyanopindolol in the presence or absence of hydrophilic (CGP-12177A) or lipophilic (propranolol) unlabeled ligands. The number of β-AR(surface) increased after exercise from 1,524.4 ± 321.4 to 3,432.6 ± 503.3 sites/cell (p < 0.01), whereas that of β-AR(intra) decreased from 356.2 ± 85.7 to 190.3 ± 60.2 sites/cell (p < 0.05). The isoproterenol-stimulated cAMP production per 1 x 106 lymphocytes after exercise was significantly higher than that at rest. However, the cAMP production per single β-AR(surface) tended to be tower after exercise. No differences between the trained and untrained subjects were found in β-AR numbers or intracellular cAMP levels. These findings demonstrate that maximal exercise induces the translocation of β-AR from intracellular sites to the cell surface in human lymphocytes. However, this translocation accounts for only 10% of the increase in total cellular β-AR, suggesting that other mechanisms are predominant and contribute substantially to the increase in β-AR(surface).