RESUMO
To investigate whether ATP-sensitive K+ channels exist in gastric smooth muscle of the guinea pig and whether they are modulated by substance P, we recorded lemakalim-activated K+ currents from freshly isolated cells using the standard whole-cell configuration. With 0.1 mM ATP and 140 mM K+ in the pipette and 90 mM K+ in the bath solution and a holding potential of -80 mV, lemakalim (10 microM) activated a glibenclamide-sensitive inward current with a mean amplitude of -224+/-34 pA. These currents were voltage-independent from -90 to 0 mV and K+-selective. Increasing the intracellular ATP concentrations from 0.1 to 3 mM reduced the lemakalim-activated currents by about five-fold. External barium and cesium inhibited the lemakalim-activated currents in a dose-dependent manner. External tetraethylammonium (10 mM) inhibited the lemakalim-activated currents by 66+/-15%. Bath application of substance P (5 microM) inhibited the lemakalim-activated currents by 53+/-13% and this inhibition was absent when 0.5 mM guanosine 5'-O-(2-thiodiphosphate) (GDPbetaS) was in the pipette. Phorbol 12,13-dibutyrate (PDB) inhibited the lemakalim-activated currents by 71+/-3%. Chelerythrine (1 microM) reduced the substance P-induced inhibition of lemakalim-activated currents by 22.2+/-11.3%. These results suggest the presence of ATP-sensitive K+ channels in gastric smooth muscle and that substance P inhibits ATP-sensitive K+ channels via G-protein through protein kinase C activation.
Assuntos
Trifosfato de Adenosina/fisiologia , Músculo Liso/efeitos dos fármacos , Canais de Potássio/efeitos dos fármacos , Substância P/farmacologia , Potenciais de Ação/efeitos dos fármacos , Potenciais de Ação/fisiologia , Animais , Bário/farmacologia , Césio/farmacologia , Cromakalim/farmacologia , Feminino , Glibureto/farmacologia , Cobaias , Hipoglicemiantes/farmacologia , Masculino , Potenciais da Membrana/efeitos dos fármacos , Potenciais da Membrana/fisiologia , Contração Muscular/efeitos dos fármacos , Contração Muscular/fisiologia , Músculo Liso/citologia , Músculo Liso/fisiologia , Técnicas de Patch-Clamp , Potássio/metabolismo , Canais de Potássio/fisiologia , Antro Pilórico/citologia , Antro Pilórico/efeitos dos fármacos , Antro Pilórico/fisiologia , Tetraetilamônio/farmacologia , Vasodilatadores/farmacologiaRESUMO
The present study was to investigate a role for endothelium-derived nitric oxide (EDNO) system in the development and maintenance of 2-kidney, 1 clip (2K1C) hypertension. Effects of blocking the synthesis or supplementing the precursor of EDNO on the developmental phase of hypertension were examined in 2K1C rats. Responses of the isolated vasculature to phenylephrine, acetylcholine, sodium nitroprusside, and atrial natriuretic peptide were also examined in chronic 2K1C rats. Ingestion of NG-nitro-L-arginine methyl ester or L-arginine did not affect the development of hypertension in 2K1C rats. Contraction response to phenylephrine was enhanced and relaxation response to acetylcholine was attenuated in the thoracic aortic ring isolated from chronic hypertensive rats, both being more marked in the 12-week hypertensive than in the 7-week hypertensive. Indomethacin did not significantly affect the degree of the attenuated vasorelaxation response to acetylcholine. The vasorelaxation response to sodium nitroprusside and atrial natriuretic peptide remained unaltered in the hypertensives. These results indicate that EDNO does not affect the developmental phase of 2K1C hypertension, whereas an impaired endothelium-dependent vasorelaxation is associated with chronic 2K1C hypertension.