Thyroid status and postnatal changes in subsarcolemmal distribution and isoform expression of rat cardiac dihydropyridine receptors.
OBJECTIVE
The aim was to analyze the early postnatal changes in myocardial density, subsarcolemmal localization and isoform expression of dihydropyridine receptors in rat ventricle and the influence of thyroid status on these changes.


METHODS
Newborn rats were treated from postnatal day 2 with L-triiodothyronine (T3) or 6-n-propyl-2-thiouracil )PTU) and ventricles were collected on day 1, 7 and 14. Radioligand binding and cell fractionation (density gradient centrifugation) techniques were used to determine the tissue density of various receptors and their subcellular localization. To analyze dihydropyridine receptor alpha 1 subunit isoform expression, cDNA fragments corresponding to a large portion of motif IV were amplified by reverse transcriptase-polymerase chain reaction and treated with appropriate restriction endonucleases to determine the frequency of splicing events at the level of motif IV.


RESULTS
The myocardial density of dihydropyridine receptors increased 3-fold from day 1 to day 14 in control rats, and this increase occurred predominantly in membrane entities equilibrating at high densities in sucrose gradient, that is, presumably, in junctional structures (dyadic couplings). This maturation was delayed after PTU-treatment, and somewhat accelerated by excess T3. The proportion of mRNA variants typical of foetal heart (IVS3A variant and 'deleted' variant, showing a 33-nucleotide deletion at the level of the extracellular loop between IVS3 and IVS4) decreased with age in control rats. This reduction was delayed after treatment with PTU but was not influenced by excess T3.


CONCLUSIONS
Hypothyroidism impaired the early postnatal maturation of dihydropyridine receptors as regards both their concentration into junctional structures and the decrease in the relative expression of alpha 1-subunit mRNA variants typical of foetal heart.
Wibo
M
M
Laboratoire de Pharmacologie, Université Catholique de Louvain, Brussels, Belgium. wibo@farl.ucl.ac.be
Feron
O
O
Zheng
L
L
Maleki
M
M
Kolar
F
F
Godfraind
T
T
D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn / Q000378:metabolism*; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D005318:Fetal Heart / Q000378:metabolism; D007536:Isomerism; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D011441:Propylthiouracil; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012508:Sarcolemma / Q000378:metabolism*; D013963:Thyroid Hormones / Q000378:metabolism*; D014284:Triiodothyronine
D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D012333:RNA, Messenger; D013963:Thyroid Hormones; D014284:Triiodothyronine; D011441:Propylthiouracil