Participation of the sarcolemma in the control of relaxation of the mammalian heart during perinatal development.
Stereological measurement of cell diameter and cell surface-to-volume ratio (S/V) were compared in fetal, newborn, and adult rabbit and frog hearts. In the frog heart, S/V was high (1.32 micron-1), comparable to that of the fetal rabbit heart (1.03 micron-1). Only 8 days after birth, cell diameter increased while S/V progressively decreased towards the adult value of 0.30 micron-1. The possible implications of the S/V decrease were investigated on the relaxation of cardiac contraction. Unlike the relaxation of the adult mammalian heart, but like that of the frog, relaxation of the fetal heart was sensitive to a reduction of Na+-Ca2+ exchange by a low-Na+ medium. With perinatal development, the participation of Na+-Ca2+ exchange in relaxation decreased and was progressively masked by the sarcoplasmic reticulum and/or other systems.
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D005260:Female; D007473:Ion Channels / Q000378:metabolism; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology*; D011247:Pregnancy; D011817:Rabbits; D011898:Ranidae; D012508:Sarcolemma / Q000378:metabolism / Q000648:ultrastructure*; D012964:Sodium / Q000378:metabolism
D007473:Ion Channels; D002110:Caffeine; D012964:Sodium; D002118:Calcium