A study by Davies et al. (A-17) was motivated by the fact that, in previous studies of contractile responses to b-adrenoceptor agonists in single myocytes from failing and nonfailing human hearts, they had observed an age-related decline in maximum response to isoproterenol, at frequencies where the maximum response to high Ca2þ in the same cell was unchanged. For the present study, the investigators computed the isoproterenol/Ca2þ ratio (ISO/CA) from measurements taken on myocytes from patients ranging in age from 7 to 70 years. Subjects were classified as older (> 50 years) and younger. The following are the (ISO/CA) values, age, and myocyte source of subjects in the study. Myocyte sources were reported as donor and biopsy.

Age ISO/CA Myocyte Source 7 1.37 Donor 21 1.39 Donor 28 1.17 Donor 35 0.71 Donor 38 1.14 Donor 50 0.95 Donor 51 0.86 Biopsy 52 0.72 Biopsy 55 0.53 Biopsy 56 0.81 Biopsy 61 0.86 Biopsy 70 0.77 Biopsy Source: Data provided courtesy of Dr. Sian E. Harding.