Prostaglandin receptors mediate effects of substances released from ischaemic rat hearts on non-ischaemic cardiomyocytes.
BACKGROUND
After ischaemia and during reperfusion, rat hearts release cardiodepressive substances that are putatively cyclooxygenase-2-dependent. The present study analyses the mechanisms by which these substances mediate their effect downstream of cyclooxygenase-2.


METHODS
After 10 min of global stop-flow ischaemia, isolated rat hearts were reperfused and post-ischaemic coronary effluent was collected over a period of 30 s. Non-ischaemic effluent collected before ischaemia was used as a control. We investigated the effect of the effluents on cell shortening and Ca(++)-metabolism, by application of fluorescence microscopy of field-stimulated adult rat cardiomyocytes incubated with fura-2. Cells were pre-incubated with inhibitors of protein kinase A and C and with antagonists of protein kinase A-dependent prostaglandin receptors. We examined the expression of prostaglandin receptors in cardiomyocytes by Western blotting.


RESULTS
In contrast to non-ischaemic effluent, post-ischaemic effluent induced reduction of Ca(++) transient and cell shortening in the cardiomyocytes. In contrast to protein kinase C inhibitor Myr-PKC [19-27], the protein kinase A inhibitor Rp-cAMPS completely blocked the effect of post-ischaemic effluent. Furthermore, we determined a cyclic adenosine monophosphate increase in cardiomyocytes that were pre-incubated with post-ischaemic effluent. The antagonist of prostaglandin E-receptor EP2 AH6809 and the antagonist of receptor subtype EP4 AH23848 attenuated the effect of post-ischaemic effluent in contrast to other antagonists of prostaglandin D and I receptors, which did not influence the effect. In lysates of adherend cardiomyocytes, expression of prostaglandin D, E and I receptors was detected by Western blotting.


CONCLUSIONS
The effect of post-ischaemic effluent is mediated by the protein kinase A-dependent prostaglandin-receptor subtypes EP2 and EP4 downstream of cyclooxygenase-2.
Birkenmeier
K
K
Klinik für Innere Medizin B, Ernst-Moritz-Amdt-Universität Greifswald, Greifswald, Germany.
Janke
I
I
Schunck
W-H
WH
Trimpert
C
C
Krieg
T
T
Landsberger
M
M
Völker
U
U
Felix
S B
SB
Staudt
A
A
D000818:Animals; D015153:Blotting, Western; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D016861:Cyclooxygenase Inhibitors / Q000378:metabolism; D006321:Heart / Q000187:drug effects*; D017202:Myocardial Ischemia / Q000378:metabolism*; D015425:Myocardial Reperfusion; D032383:Myocytes, Cardiac / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D011982:Receptors, Prostaglandin / Q000037:antagonists & inhibitors / Q000502:physiology*
D016861:Cyclooxygenase Inhibitors; D011982:Receptors, Prostaglandin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C