title: Cardiac Na+-H+ exchanger during postnatal development in the rat: changes in mRNA expression and sarcolemmal activity.
abstract: We examined Na+-H+ exchanger isoform 1 (NHE-1) mRNA expression in ventricular myocardium and its correlation with sarcolemmal NHE activity in isolated ventricular myocytes, during postnatal development in the rat. The expression of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) mRNA did not change in ventricular myocardium between 2 and 42 days after birth. Therefore, at seven time points within that age range. GAPDH expression was used to normalize NHE-1 mRNA levels, as determined by reverse transcription polymerase chain reaction analysis. There was a progressive five-fold reduction in NHE-1 mRNA expression in ventricular myocardium from 2 days to 42 days of age. As an index of NHE activity, acid efflux rates (J(H)) were determined in single neonatal (2-4-day-old) and adult (42-day-old) ventricular myocytes (n=16/group) loaded with the pH fluoroprobe carboxy-seminaphthorhodafluor-1. In HEPES-buffered medium, basal intracellular pH (pH(i)) was similar at 7.28+/-0.02 in neonatal and 7.31+/-0.02 in adult myocytes, but intrinsic buffering power was lower in the former age group. The rate at which pH(i) recovered from a similar acid load was significantly greater in neonatal than in adult myocytes (0.36+/-0.07 v 0.16+/-0.02 pH units/min at pH(i)=6.8). This was reflected by a significantly greater J(H) (22+/-4 v 9+/-1 pmol/cm2/s at pH(i)=6.8), indicating greater sarcolemmal NHE activity in neonatal myocytes. The concomitant reductions in tissue NHE-1 mRNA expression and sarcolemmal NHE activity suggest that myocardial NHE-1 is subject to regulation at the mRNA level during postnatal development.
authors.affiliation: Cardiovascular Research, The Rayne Institute, St Thomas' Hospital, London, UK.
authors.forename: R S
authors.initials: RS
authors.lastname: Haworth
authors.forename: M
authors.initials: M
authors.lastname: Yasutake
authors.forename: G
authors.initials: G
authors.lastname: Brooks
authors.forename: M
authors.initials: M
authors.lastname: Avkiran
mesh_terms: D000818:Animals; D002021:Buffers; D048429:Cell Size; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000235:genetics; D006352:Heart Ventricles / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D012333:RNA, Messenger / Q000096:biosynthesis*; D051381:Rats; D017208:Rats, Wistar; D012508:Sarcolemma / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics*; D013499:Surface Properties
chemical_list: D002021:Buffers; D012333:RNA, Messenger; D017923:Sodium-Hydrogen Exchangers; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases