Na+/Ca2+ exchange current and contractions measured under Cl(-)-free conditions in developing rabbit hearts.
Previous studies suggesting a greater functional role of cardiac Na+/Ca2+ exchange at birth were performed using tightly buffered free cytosolic Ca2+ concentration ([Ca2+]i). Because Na+/Ca2+ exchange current (INaCa) is influenced by physiological fluctuations in [Ca2+]i, we used conditions of minimally buffered [Ca2+]i to simultaneously record INaCa and cell contractions in single ventricular myocytes isolated from 1 to 27-day-old and adult rabbits. With conventional Cl(-)-containing solutions. Ni(2+)-sensitive outward and inward charge movements were unbalanced, suggesting the presence of a contaminating current (presumably the Ca(2+)-activated Cl- current). Removing Cl- abolished this discrepancy in all age groups and allowed for the accurate quantitation of INaCa. Under Cl(-)-free conditions, outward and inward charge movements were high at birth (4 days: 0.42 +/- 0.03 and -0.38 +/- 0.04 pC/pF, respectively) and decreased postnatally (adult: 0.08 +/- 0.01 and -0.07 +/- 0.01 pC/pF, respectively). Newborn but not adult myocytes contracted during depolarizations in the presence of nifedipine, ryanodine, and thapsigargin. The magnitudes of outward charge movement (Ca2+ influx) and cell shortening exhibited similar voltage dependence, consistent with INaCa-mediated contractions. These results indicate that INaCa can directly support contraction in newborn rabbit ventricular myocytes.
Haddock
P S
PS
Department of Pediatrics, New York University Medical Center, New York 10016, USA.
Coetzee
W A
WA
Artman
M
M
D000375:Aging / Q000378:metabolism; D000818:Animals; D002352:Carrier Proteins / Q000187:drug effects / Q000502:physiology*; D002469:Cell Separation; D002712:Chlorides / Q000494:pharmacology* / Q000502:physiology; D004553:Electric Conductivity; D004594:Electrophysiology; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009532:Nickel / Q000494:pharmacology; D011817:Rabbits; D011930:Reaction Time; D019831:Sodium-Calcium Exchanger; D012996:Solutions
D002352:Carrier Proteins; D002712:Chlorides; D019831:Sodium-Calcium Exchanger; D012996:Solutions; D009532:Nickel