Interaction between cyclic GMP protein kinase and cyclic AMP may be diminished in stunned cardiac myocytes

We tested the hypothesis that the importance of the negative functional eff ects of the cyclic GMP protein kinase would be reduced in stunned (simulate d ischemia/reperfusion) cardiac myocytes. Ventricular cardiac myocytes were isolated from New Zealand white rabbits (N = 7). Myocytes were studied at baseline and after simulated ischemia (15 min of 95% N-2-5% CO2 at 37 degre esC) followed by simulated reperfusion (reoxygenation). Cell shortening was studied with a video edge detector; O-2 consumption was measured using O-2 electrodes. Protein phosphorylation was measured autoradiographically afte r gel electrophoresis. Functional and metabolic data were acquired after: ( 1) 8-(4-chlorophenylthio)guanosine-3',5'-monophosphate (PCPT, cGMP protein kinase agonist) 10(-7) or 10(-5) M; (2) 8-Br-cAMP 10(-5) M followed by PCPT 10(-7) or 10(-5) M; (3) beta -phenyl-1, N-2-etheno-8-bromoguanosine-3',5'- monophosphorothioate, SP-isomer (SP, cGMP protein kinase agonist) 10(-7) or 10(-5) M; (2) 8-Br-cAMP 10(-5) M followed by SP 10(-7) or 10(-5) M. At bas eline, percent of shortening (Pcs) and maximal rate of shortening (Rs) were significantly lower in the stunned myocytes (Pcs: 5.0 +/- 0.2% control vs. 3.8 +/- 0.3 stunned; Rs: 64.8 +/- 5.9 mum/s control vs. 46.9 +/- 4.8 stunn ed). In both groups, PCPT and SP dose-dependently decreased Pcs and Rs. The effects were slightly, but not significantly, less in stunned myocytes. 8- Br-cyclic AMP significantly increased function in control, but not stunned myocytes (Pes, 4.5 +/- 0.5 to 6.2 +/- 0.8 control vs. 3.1 +/- 0.2 to 3.6 +/ - 0.2 stunned). The negative functional effects of PCPT and SP were diminis hed after 8-Br-cyclic AMP in control (from -39% to - 29%) and diminished si gnificantly more in the stunned myocytes (- 19%). PCPT and cyclic AMP phosp horylated similar protein bands. In stunned myocytes, three (22, 31 and 53 kDa) bands were enhanced less by PCPT. (C) 2001 Elsevier Science B.V. All r ights reserved.