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. Materials and 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.