Na+/Ca2+ exchange activity in neonatal rabbit ventricular myocytes.
Much less is known about the contributions of the Na(+)/Ca(2+) exchanger (NCX) and sarcoplasmic reticulum (SR) Ca(2+) pump to cell relaxation in neonatal compared with adult mammalian ventricular myocytes. Based on both biochemical and molecular studies, there is evidence of a much higher density of NCX at birth that subsequently decreases during the next 2 wk of development. It has been hypothesized, therefore, that NCX plays a relatively more important role for cytosolic Ca(2+) decline in neonates as well as, perhaps, a role in excitation-contraction coupling in reverse mode. We isolated neonatal ventricular myocytes from rabbits in four different age groups: 3, 6, 10, and 20 days of age. Using an amphotericin-perforated patch-clamp technique in fluo-3-loaded myocytes, we measured the caffeine-induced inward NCX current (I(NCX)) and the Ca(2+) transient. We found that the integral of I(NCX), an indicator of SR Ca(2+) content, was greatest in myocytes from younger age groups when normalized by cell surface area and that it decreased with age. The velocity of Ca(2+) extrusion by NCX (V(NCX)) was linear with [Ca(2+)] and did not indicate saturation kinetics until [Ca(2+)] reached 1-3 microM for each age group. There was a significantly greater time delay between the peaks of I(NCX) and the Ca(2+) transient in myocytes from the youngest age groups. This observation could be related to structural differences in the subsarcolemmal microdomains as a function of age.
Cardiac Membrane Research Laboratory, Simon Fraser University, Burnaby, British Columbia, Canada.
Jingbo
J
Huang
Leif
L
Hove-Madsen
Glen F
GF
Tibbits
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006321:Heart / Q000254:growth & development / Q000502:physiology*; D006352:Heart Ventricles / Q000166:cytology / Q000254:growth & development; D007211:Indoles / Q000494:pharmacology; D008297:Male; D032383:Myocytes, Cardiac / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology; D012508:Sarcolemma / Q000502:physiology; D019831:Sodium-Calcium Exchanger / Q000502:physiology*; D016276:Ventricular Function
D004791:Enzyme Inhibitors; D007211:Indoles; D019831:Sodium-Calcium Exchanger; D012433:Ryanodine; D002118:Calcium; C000543:cyclopiazonic acid