The NHE3 inhibitor AVE1599 stimulates phrenic nerve activity in the rat

The effect of AVE1599, an inhibitor of the sodium/proton exchanger type 3 (NHE3), on phrenic nerve (PN) activity was investigated using the working heart brainstem preparation (WHBP). Hypercapnia (Delta pH: -0.1) applied for 10 min reversibly increased PN frequency (f) by 66.0 +/- 19.5% and decreased burst duration by 23.3 +/- 3% (mean +/- SE, n = 21). Similarly, AVE1599 (0.3 microM) increased f after 10 and 30 min by 75.1 +/- 13.2 and 176 +/- 36.2% (n = 10), respectively, and reduced duration of PN bursts by 24.9 +/- 10.8%. Hypercapnia-induced increases of f were attenuated by AVE1599. An elevated concentration of AVE1599 (0.9 microM) had no significant effect on PN. As AVE1599 accumulates in brain tissue and might interfere with the less affine NHE1, we furthermore tested the NHE1-inhibitor HOE642. In fact, HOE642 (0.9 microM) diminished f by 88.5 +/- 9.2 and 58.6 +/- 10.0% after 10 and 30 min (n = 6), respectively, but did not abolish hypercapnic responses. We conclude that AVE1599 augments central respiratory drive in the WHBP via NHE3 but not NHE1 inhibition.