Abstract

The actions of 8-tert-butyl-6,7-dihydropyrolo[3,2-e]-5- methylpyrazolo[1,5-a]pyrimidine-3-carbonitrile (LP-805) on membrane K+ currents in cultured bovine pulmonary artery endothelial cells were investigated using the patch-clamp technique. In the whole-cell voltage clamp experiments, with 11 mM ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) in the pipette, membrane currents revealed only an inwardly rectifying K+ current, and no outward current could be observed at depolarized potentials. Using a pipette solution containing 0.3 mM EGTA, outward K+ current was present in response to depolarizing voltage steps from a holding potential of -60 mV. LP-805 (1-10 microM) significantly increased outward K+ currents in a concentration-dependent manner. The increase of this K+ current was inhibited by 5 mM tetraethylammonium and 5 mM tetrabutylammonium to a level less than the control. Partial recovery occurred on washout. However, the increase of outward K+ current by 10 microM LP-805 was unaffected by 5 mM 4-aminopyridine and 1 microM glibenclamide. LP-805 (1-10 microM) significantly decreased the inwardly rectifying K+ current in a concentration-dependent manner. In cell-attached patches, inward single K+ currents were recorded at negative membrane potentials, and single channel conductance was 23 +/- 2 pS (n = 5). No outward current could be observed at positive potentials. LP-805 (10 microM) inhibited the inwardly rectifying K+ currents. Thus LP-805 inhibits inwardly rectifying K+ currents but activates outward Ca(++)-dependent K+ currents in bovine pulmonary artery endothelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)