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Am J Physiol Heart Circ Physiol 285: H90-H96, 2003. First published March 13, 2003; doi:10.1152/ajpheart.01018.2002
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Age-related functional effects linked to phosphatase activity in ventricular myocytes

Elizabeth M. Grey, Chun K. Chan, Yi Chen, and Polly A. Hofmann

Department of Physiology, University of Tennessee, Memphis, Tennessee 38163

Submitted 25 November 2002 ; accepted in final form 12 March 2003

Conflicting reports exist regarding the influence of {beta}-adrenergic stimulation on the maximum velocity of shortening (Vmax) in ventricular myocytes. This may be due to an unrecognized effect of maturation. In the present study, the effects of {beta}-adrenergic receptor stimulation on myocytes from hearts of juvenile nonbred and young adult retired breeder female rats were compared. Ventricular myocytes from young adults had a {beta}-adrenergic-dependent increase in Vmax and Ca2+-dependent actomyosin ATPase that was not observed in myocytes from juveniles. Myocytes from young adults had both an increase in {beta}-myosin heavy chain (MHC) and higher basal serine/threonine phosphatase activity compared with juvenile rats. Additional studies established moderate increases in {beta}-MHC induced by hypothyroidism do not confer myocardial {beta}-adrenergic responsiveness, whereas inhibition of the higher phosphatase activity in myocytes from young adults blocks the age-dependent, {beta}-adrenergic-induced increase in cross-bridge cycling rates. We propose that the higher phosphatase activity of myocytes from young adults compared with juveniles allows for a greater functional response of the myocardium to {beta}-adrenergic stimulation.

{beta}-adrenergic; heart; maturation; velocity of shortening


Address for reprint requests and other correspondence: P. A. Hofmann, Dept. of Physiology, Univ. of Tennessee, 894 Union Ave., Memphis, TN 38163 (E-mail: phofmann{at}physio1.utmem.edu).






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