© 1996 by European Society of Cardiology
Copyright © 1996, European Society of Cardiology
Contribution of sarcolemmal calcium current to total cellular calcium in postnatally developing rat heart
Department of Biology, University of Joensuu, P.O. Box 111, SF-80101 Joensuu, Finland
* Fax (+358) 731513590. Vornanen{at}joyl.joensuu.fi
Objective: The aim was to determine the contribution of sarcolemmal Ca influx through L-type Ca current to total cellular Ca in newborn and postnatally developing rat heart. Methods: Whole cell voltage clamp was used to study L-type Ca current in freshly isolated ventricular cells of 1, 6, 10, 15, 30-day-old and adult (120–150 days) rats. Amplitude, current density, inactivation rate and time integral of Ca current were determined at the experimental temperature of 36 °C. Width, length, surface area, volume and surface-to-volume ratio of the isolated cells were also determined. Using the time integral of Ca current and volume of the myocytes the increment in total cellular Ca was calculated for the six developmental stages. Results: The amplitude of Ca current increased strongly during the postnatal maturation from 277 ± 25 pA at day 1 to 1961 ± 98 pA in the adult rat (P < 0.001). This increase was due to an almost proportional increase in cell size; accordingly the density of Ca current remained fairly constant, being 16.9 ± 1.8, 17.0 ± 1.8, 22.8 ± 1.4, 21.2 ± 1.5, 16.2 ± 2.0 and 15.9 ± 0.7 pA/pF for 1, 6, 10, 15, 30-day-old and adult rats, respectively. Charge transfer by Cd-sensitive Ca current during 200 ms voltage pulse from –45 mV to 0 mV increased from 7.18 ± 1.00 pC at day one to 24.80 ± 1.80 pC in the adult rat heart (P < 0.001). When normalized to the capacitive surface area of the myocytes the charge transfer by L-type Ca current was more than double in newborns (0.429 ± 0.074 pC/pF) as compared to the adults (0.188 ± 0.016 pC/pF) (P < 0.01). The difference is explained by slower inactivation rate of Ca current in newborn than adult rats. Time constant of the fast component was 5.92 ± 0.62 ms and 4.5 ± 0.4 ms (P < 0.05) for 1-day-old and adult rat, respectively. Time constant of the slow component decreased from 27.7 ± 2.0 to 21.7 ± 3.0, although the difference was not statistically significant (P = 0.26). The increment in total cellular Ca due to Ca influx through Ca channels was 54 ± 9 µmol l–1 in 1-day-old rat and decreased steadily during postnatal maturation to 8 ± 1 µmol l–1 in the adult rat (P < 0.001). The change is partly due to faster inactivation of Ca current in adults but mainly as a consequence of decreasing surface-to-volume ratio of growing myocytes. Sarcolemmal surface area increases almost 9 times from 1.001 x 103 µm2 at day 1 to 8.675 x 103 µm2 for the adult rat, whereas increase in cell volume is about 28-fold from 0.991 x 103 to 27.74 x 103 µm3: accordingly surface-to-volume ratio decreases from 1.05 ± 0.02 at day 1 to 0.36 ±0.01 in the adult rat (P < 0.01). Conclusions: Contribution of sarcolemmal Ca influx through L-type Ca channels is over 6 times higher in newborn than mature rats. Therefore, the strong dependence of neonatal rat heart on extracellular Ca for contractile activation is, at least partially, explained by greater contribution of L-type Ca current to intracellular Ca.
KEYWORDS Calcium channel, L-type; Age; Development; Calcium fluxes; Calcium, intercellular concentration; Cell size; Excitation—contraction coupling; Rat, ventricular myocytes
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  L. J. Wang and E. A. Sobie Mathematical model of the neonatal mouse ventricular action potential Am J Physiol Heart Circ Physiol, June 1, 2008; 294(6): H2565 - H2575. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. Huang, L. Xu, M. Thomas, K. Whitaker, L. Hove-Madsen, and G. F. Tibbits L-type Ca2+ channel function and expression in neonatal rabbit ventricular myocytes Am J Physiol Heart Circ Physiol, June 1, 2006; 290(6): H2267 - H2276. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. L. Escobar, R. Ribeiro-Costa, C. Villalba-Galea, M. E. Zoghbi, C. G. Perez, and R. Mejia-Alvarez Developmental changes of intracellular Ca2+ transients in beating rat hearts Am J Physiol Heart Circ Physiol, March 1, 2004; 286(3): H971 - H978. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. A. Bassani and J. W. M. Bassani Contribution of Ca2+ transporters to relaxation in intact ventricular myocytes from developing rats Am J Physiol Heart Circ Physiol, June 1, 2002; 282(6): H2406 - H2413. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M Vornanen Na+/Ca2+ exchange current in ventricular myocytes of fish heart: contribution to sarcolemmal Ca2+ influx J. Exp. Biol., January 7, 1999; 202(13): 1763 - 1775. [Abstract] [PDF]
|
|
|
|
 |
|
 M. Wibo, O. Feron, L. Zheng, M. Maleki, F. Kolar, and T. Godfraind Thyroid status and postnatal changes in subsarcolemmal distribution and isoform expression of rat cardiac dihydropyridine receptors Cardiovasc Res, January 1, 1998; 37(1): 151 - 159. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. A. Bassani and J. W. M. Bassani Contribution of Ca2+ transporters to relaxation in intact ventricular myocytes from developing rats Am J Physiol Heart Circ Physiol, June 1, 2002; 282(6): H2406 - H2413. [Abstract] [Full Text] [PDF]
|
|