A1 adenosine receptors modulate respiratory activity of the neonatal mouse via the cAMP-mediated signaling pathway

The effects of adenosine and its analogs on the function of the respiratory center were studied in the spontaneously active rhythmic slice of neonatal and juvenile mice (4-14 days old). Whole cell, spontaneous postsynaptic currents (sPSCs) and single channel K-ATP currents were recorded in inspiratory neurons of the pre-Botzinger complex. Adenosine (50-600 mu M) inhibited the respiratory rhythm. This was accompanied by increase in the activity of K-ATP channels in cell-attached patches. The A(1) adenosine receptor agonist, 2-chloro-N-6-cyclopentyladenosine (CCPA, 0.3-2 mu M), inhibited the respiratory rhythm, sPSCs, and enhanced activity of K-ATP channels. The A(1) adenosine receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 1-3 mu M), showed opposite effects and occluded the CCPA actions. Agents specific for A(2) adenosine receptors (CGS 21860 and NECA, both applied at 1-10 mu M) were without effect. Elevation of intracellular cAMP concentration ([cAMP]i) by 8-Br-cAMP (200-500 mu M), forskolin (0.5-2 mu M), or isobutylmethylxantine (IBMX, 30-90 mu M) reinforced the rhythm, whereas NaF (100-800 mu M) depressed it. The open probability of single K-ATP channels in cell-attached patches decreased after application of forskolin and increased in the presence of NaF. [cAMP](i) elevation reversed the effects of A(1) receptors both on the respiratory rhythm and K-ATP channels. A(1) receptors and [cAMP](i) modified the hypoxic respiratory response. In the presence of A(1) agonists the duration of hypoxic augmentation shortened, and depression of the respiratory rhythm occurred earlier. Elevation of [cAMP](i) prolonged augmentation and delayed the development of the depression. We conclude that A(1) adenosine receptors modulate the respiratory rhythm via inhibition of intracellular cAMP production and concomitant activation of K-ATP channels.