Parathyroid hormone improves contractile performance of adult rat ventricular cardiomyocytes at low concentrations in a non-acute way.
OBJECTIVE
In patients with congestive heart failure, plasma parathyroid hormone (PTH) levels are positively associated with cardiac function. PTH, used to mobilize stem cells from the bone marrow after myocardial infarction, causes an increased left ventricular ejection fraction. The aim of this study was to investigate whether low but plasma-relevant concentrations of PTH directly influence the contractile properties of cardiomyocytes.


RESULTS
Isolated adult rat ventricular cardiomyocytes were exposed to PTH(1-34) or full-length PTH at picomolar concentrations for 24 h. Cell shortening was measured at 2 Hz as a cellular correlate of inotropic responsiveness. Intracellular calcium was measured in Fura-AM-loaded cells. PTH(1-3) (20-200 pM) and full-length PTH (200 pM) increased cell shortening within 24 h. PTH had no effect on cell size, but resting and peak systolic calcium concentrations were elevated. The beneficial effect of PTH was mediated via its cAMP/protein kinase A-activating domain and attenuated by addition of a protein kinase A inhibitor. In contrast, PTH peptides representing a protein kinase C-activating domain but not a cAMP/protein kinase A-activating domain or peptides that represent none of these domains had no effect on cell shortening. The effect of PTH on cell shortening was strong at low concentrations of extracellular calcium but declined at higher calcium concentrations. PTH downregulated the expression of the calcium sensing receptor, a receptor known to antagonize the action of PTH on calcium transport. Furthermore, PTH antagonized the angiotensin II-induced loss of cell function.


CONCLUSIONS
Low concentrations of PTH improve cell shortening by increasing calcium load at rest. By this mechanism cardiomyocytes compensate reduced extracellular calcium levels as they occur in patients with heart failure.
Tastan
Ilhan
I
Justus-Liebig-Universität Giessen, Physiologisches Institut, Aulweg 129, D-35392 Giessen, Germany.
Schreckenberg
Rolf
R
Mufti
Solaiman
S
Abdallah
Yaser
Y
Piper
Hans Michael
HM
Schlüter
Klaus-Dieter
KD
D000804:Angiotensin II / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002304:Cardiac Pacing, Artificial; D048430:Cell Shape; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D044169:Receptors, Calcium-Sensing / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors
D010281:Parathyroid Hormone; D010446:Peptide Fragments; D047428:Protein Kinase Inhibitors; D044169:Receptors, Calcium-Sensing; D000804:Angiotensin II; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D002118:Calcium