Guanosine 3 ': 5 '-cyclic monophosphate-dependent pathway alterations in ventricular cardiomyocytes of spontaneously hypertensive rats

1 We investigated the effect of the NO-donor S-nitroso-N-acetyl-DL-penicill amine (SNAP) on cardiomyocytes isolated from control normotensive Wistar Ky oto (WKY) and spontaneously hypertensive (SHR) rats. 2 Ventricular cardiomyocytes were isolated from SHR and WKY hearts and imag ing analysis of fura-2-loaded cells was performed in order to evaluate calc ium transient in electrical field paced (0.5 Hz) cells. 3 In WKY cardiomyocytes, 1-200 mum SNAP dose-dependently increased cyclic G MP content. In basal conditions, cyclic GMP content of SHR cardiomyocytes w as significantly higher than in WKY, but SNAP failed to further increase cy clic GMP over the basal level. 4 In control conditions, the DeltaF/F and decay time of the calcium transie nt were similar in both strains. In WKY cardiomyocytes, SNAP (1-100 mum) re duced the decay time. In SHR cardiomyocytes, SNAP was ineffective. Dibutyry l cyclic GMP (10(-6)-10(-8) M), a membrane permeable cyclic GMP analogue, b ehaved similarly to SNAP. 5 In WKY and SHR cardiomyocytes, 10(-8) m isoprenaline similarly increased DeltaF/F and decreased the decay time. SNAP and dibutyryl cyclic GMP preven ted the effect of isoprenaline in WKY, whereas both molecules were ineffect ive in SHR cardiomyocytes. In WKY, SNAP effects were blocked by pretreating cells with the cGK inhibitor KT-5823. 6 Western blotting analysis of cGK type I showed that the enzyme was expres sed in WKY isolated cardiomyocytes, but absent in four out of five SHR prep arations. 7 We concluded that the low expression of cGKI may determine the lack of NO /cyclic GMP-dependent regulation on calcium transient in SHR cardiomyocytes . This alteration may contribute to the development of heart hypertrophy in hypertensive status.