Na+/Ca2+ exchange current density in cardiac myocytes from rabbits and guinea pigs during postnatal development.
It has been proposed that the activity of the cardiac sarcolemmal Na+/Ca2+ exchanger may be greatest in developing animals before the sarcoplasmic reticulum (SR) reaches functional maturity. Experiments were performed in rabbits, which have a sparse SR at birth, and in newborn guinea pigs, which exhibit a more extensive SR. Whole cell voltage clamp techniques were used to characterize the Ni(2+)-sensitive Na+/Ca2+ exchange current in single freshly isolated cardiac myocytes. Na+/Ca2+ exchange current was measured from a holding potential of -40 mV by using a slow-ramp voltage protocol (-120 to +60 mV, 0.09 V/s) in the presence of Ba2+, Cs+, tetraethylammonia, D-600, and ouabain to block Ca2+, Na+, and K+ currents. Experiments in developing rabbits (1-22 days old) demonstrated that Na+/Ca2+ exchange current density was greatest at 1-4 days and declined rapidly over the first 3 wk of age. In contrast, Na+/Ca2+ exchange current density in newborn guinea pig myocytes did not differ from that recorded in adults. These results confirm that Na+/Ca2+ exchange is functional at birth in both rabbits and guinea pigs. The species-related difference in the ontogeny of Na+/Ca2+ exchange is consistent with the concept that Na+/Ca2+ exchange assumes a relatively greater role in newborn animals with a sparse SR.
Artman
M
M
Department of Pediatrics, University of South Alabama, Mobile 36617, USA.
Ichikawa
H
H
Avkiran
M
M
Coetzee
W A
WA
D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D002352:Carrier Proteins / Q000502:physiology*; D004553:Electric Conductivity; D004594:Electrophysiology; D006168:Guinea Pigs; D009206:Myocardium / Q000378:metabolism*; D011817:Rabbits; D019831:Sodium-Calcium Exchanger
D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger