L-type Ca2+ currents in ventricular myocytes from neonatal and adult rats

Citation
Y. Katsube et al., L-type Ca2+ currents in ventricular myocytes from neonatal and adult rats, CAN J PHYSL, 76(9), 1998, pp. 873-881
Citations number
33
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Pharmacology & Toxicology
Journal title
CANADIAN JOURNAL OF PHYSIOLOGY AND PHARMACOLOGY
ISSN journal
0008-4212 → ACNP
Volume
76
Issue
9
Year of publication
1998
Pages
873 - 881
Database
ISI
SICI code
0008-4212(199809)76:9<873:LCCIVM>2.0.ZU;2-G
Abstract
Postnatal changes in the slow Ca2+ current (I-Ca(L)) were investigated in f reshly isolated ventricular myocytes from neonatal (1-7 days old) and adult (2-4 months old) rats, using whole-cell voltage clamp and single-channel r ecordings. The membrane capacitance (mean +/- SEM) averaged 23.2 +/- 0.5 pF in neonates (n = 163) and 140 +/- 4.1 pF in adults (n = 143). Ica(L) was m easured as the peak inward current at a test potential of +10 mV (or +20 mV ) by applying a 300-ms pulse from a holding potential of -40 mV; 1.8 mM Ca2 + was used as charge carrier. The basal ICa(L) density was 6.7 +/- 0.2 pA/p F in neonatal and 7.8 +/- 0.2 pA/pF in adult cells (p < 0.05). The time cou rse of inactivation of the fast component (at +10 ms) was significantly lon ger in the neonatal (10.7 +/- 1.4 ms) than in the adult (6.6 +/- 0.4 ms) ce lls (p < 0.05). Ryanodine (10 mu M) significantly increased this value to 1 8.0 +/- 1.9 in neonate (n = 8) and to 17.7 +/- 2.0 in adult (n = 9). For st eady-state inactivation, the half-inactivation potential (V-h) was not chan ged in either group. For steady-state activation, V-h was 5.1 mV in the neo natal (n = 6) and -7.9 mV in the adult cells (n = 7). Single-channel record ings revealed that long openings (mode-2 behavior) were occasionally observ ed in the neonatal cells (11 events from 1080 traces/11 cells), but not in the adult cells (400 traces/4 cells). Slope conductance was 24 pS in both t he neonatal and adult cells. Results in rat ventricular myocytes suggest th e following: (i) the peak Ca2+ current density is already well developed in the neonatal period (being about 85% of the adult value); (ii) the fast co mponent of inactivation is slower in neonates than in adults; and (iii) nat urally occurring long openings are occasionally observed in the neonatal st age but not in the adult. Thus, the L-type Ca2+ channels of the neonate wer e slightly lower in density, were inactivated more slowly, and occasionally exhibited mode-2 behavior as compared with those of the adult.