Na+/Ca2+exchange activity in neonatal rabbit ventricular myocytes

Author:

Huang Jingbo,Hove-Madsen Leif,Tibbits Glen F.

Abstract

Much less is known about the contributions of the Na+/Ca2+exchanger (NCX) and sarcoplasmic reticulum (SR) Ca2+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 Ca2+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 ( INCX) and the Ca2+transient. We found that the integral of INCX, an indicator of SR Ca2+content, was greatest in myocytes from younger age groups when normalized by cell surface area and that it decreased with age. The velocity of Ca2+extrusion by NCX ( VNCX) was linear with [Ca2+] and did not indicate saturation kinetics until [Ca2+] reached 1–3 μM for each age group. There was a significantly greater time delay between the peaks of INCXand the Ca2+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.

Publisher

American Physiological Society

Subject

Cell Biology,Physiology

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