Na+/H+ exchanger blockade is involved in the protection afforded by phosphodiesterase-5A inhibition by sildenafil after myocardial infarction. P

PÉREZ NG; ENNIS IL; GARCIARENA CD; CINGOLANI OH; CHIAPPE DE CINGOLANI GE; YANG X-P; CINGOLANI HE

Chicago, Illinois, EEUU

Congreso; 79th Scientific Sessions of The American Heart Association; 2006

An increased protein kinase G (PKG-1) activity has been reported to inhibit the Na+/H+ exchanger (NHE) activity in mesangial (NHE-1) and Caco (NHE-3) cells. The objective of this work was to evaluate if this effect can be detected in rat myocardium. The experiments were performed in isolated left ventricle papillary muscles from Wistar rats. The NHE-1 activity was evaluated by the initial (maximal) H+ efflux (JH+) from an acute acid load (ammonium prepulse) in the absence of bicarbonate, condition under which the NHE is the only operative pHi regulatory mechanism. Inhibition of the cGMP catabolic enzyme phosphodiesterase-5A (PDE5A) was induced by 1 mmol/L sildenafil (S). S did not significantly modify the immediate pHi recovery after the ammonium washout (JH+ in mmol/L/min: 0.81±0.11, n=5 in control vs. 0.68±0.05, n=4 in S). Since sustained acidosis is a common feature of different pathologies like ischemia, and it was shown that prolongation of acidosis for more than 3-5 min activate kinase pathways leading to additional increase of the NHE activity, we tested whether increasing PKG-1 activity may affect pHi recovery after sustained acidosis induced by washing out the ammonium pulse with Na+-free solution. Na+ re-addition after arbitrary selected 25 min of acidosis revealed a drastic reduction of NHE activity after S treatment (JH+ decreased from 1.50±0.06 to 0.20±0.10 mmol/L/min, n=5 each, P<0.05). This effect was reproduced by EMD360527/5 (0.1 mmol/L) another PDE5A inhibitor (JH+: 0.19±0.16 mmol/L/min, n=4, P<0.05 vs. control). To get further insight on this phenomenon the effect of the PKG inhibitor KT5823 (1 mmol/L) on the NHE-1 activity after acute inhibition of PDE5A by S was examined. Under these conditions, initial JH+ was not found to be statistically different from controls (2.13±0.61 mmol/L/min, n=4), giving support to the notion that PKG inhibition blunted the inhibitory effect of S on NHE-1 activity. KT5823 alone did not altered the initial JH+ after the acidic load (2.01±0.10 mmol/L/min, n=4). In conclusion, the results allow to propose a previously unknown PKG-mediated NHE-1 inhibition in the myocardium, manifested only after sustained acidosis, and that may explain the beneficial effects of increasing PKG activity in different pathologies