Urocortin II enhances contractility in rabbit ventricular myocytes via CRF(2) receptor-mediated stimulation of protein kinase A.
OBJECTIVE
Urocortin II (UcnII), a peptide of the corticotropin-releasing factor (CRF) family, exerts profound actions on the cardiovascular system. Direct effects of UcnII on adult cardiomyocytes have not been evaluated before. Our aim was to characterize functional effects of UcnII on cardiomyocytes and to elucidate the underlying signaling pathway(s) and cellular mechanisms.


METHODS
Rabbit ventricular cardiomyocytes were stimulated at 0.5 Hz (22-25 degrees C). Unloaded cell shortening (FS, edge detection), [Ca(2+)](i) transients (Fluo-4), and L-type Ca(2+) currents (I(Ca), whole-cell patch clamping) were measured. Sarcoplasmic reticulum (SR) Ca(2+) load was assessed by rapid application of caffeine (20 mmol/L).


RESULTS
UcnII increased cell shortening and accelerated relaxation in a time- and concentration-dependent manner (EC(50): 10.7 nmol/L). The inotropic effect of UcnII was maximal at 100 nmol/L (35%+/-11% increase in FS, n=8, P<0.05). The inotropic and lusitropic actions of UcnII were largely eliminated by inhibition of CRF(2) receptors (10 nmol/L antisauvagine-30, n=5) or protein kinase A (PKA, 500 nmol/L H-89, n=5). UcnII increased [Ca(2+)](i) transient amplitude (by 63%+/-35%, n=7, P<0.05) and decreased the time constant for decay (from 800+/-63 to 218+/-27 ms, n=7, P<0.001). UcnII also increased SR Ca(2+) load (by 19%+/-7%, n=7, P<0.05) and fractional Ca(2+) release (from 57%+/-7% to 98%+/-2%, n=7, P<0.01). I(Ca) was augmented by 32.7%+/-10.0% (n=9, P<0.05) and the I(Ca)-V relationship was shifted by -15 mV during UcnII treatment.


CONCLUSIONS
UcnII exerts positive inotropic and lusitropic effects in cardiomyocytes via CRF(2) receptor-mediated stimulation of PKA which augments I(Ca) and SR Ca(2+) load to increase SR Ca(2+) release and [Ca(2+)](i) transients.
Yang
Li-Zhen
LZ
Department of Molecular Neuroendocrinology, Max Planck Institute for Experimental Medicine, Hermann-Rein-Strasse 3, D-37075 Göttingen, Germany.
Kockskämper
Jens
J
Heinzel
Frank R
FR
Hauber
Michael
M
Walther
Stefanie
S
Spiess
Joachim
J
Pieske
Burkert
B
D000818:Animals; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation; D006352:Heart Ventricles; D018613:Microscopy, Confocal; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology; D011817:Rabbits; D018019:Receptors, Corticotropin-Releasing Hormone / Q000378:metabolism*; D013268:Stimulation, Chemical; D054832:Urocortins
D010446:Peptide Fragments; D018019:Receptors, Corticotropin-Releasing Hormone; D054832:Urocortins; C116607:antisauvagine 30; D003346:Corticotropin-Releasing Hormone; D017868:Cyclic AMP-Dependent Protein Kinases