Inhibition of amiloride-sensitive apical Na+ conductance by acetylcholine in rabbit cortical collecting duct perfused in vitro.
We examined effects of acetylcholine (ACh) on the electrical parameters and intracellular Ca2+ concentration ([Ca2+]i) in the isolated rabbit cortical collecting duct (CCD) perfused in vitro using the conventional microelectrode technique and microscopic fluorescence spectrophotometry. ACh (10(-8) to 10(-5) M) in the bath caused a positive deflection of the transepithelial voltage (VT) and an increase in [Ca2+]i. Carbachol also showed similar but smaller effects. The effects of ACh were antagonized by muscarinic receptor antagonists. ACh at 10(-6) M hyperpolarized the apical membrane voltage and increased the fractional resistance of the apical membrane of the collecting duct cells accompanied by a positive deflection of VT and an increase in transepithelial resistance, whereas it did not affect these parameters in the beta-intercalated cells. In the presence of 10(-5) M amiloride in the lumen, the effects of ACh were almost completely abolished. The ACh-induced increase in [Ca2+]i is accounted for by the release of Ca2+ from intracellular store and Ca2+ entry from the bath. In the absence of Ca2+ in the bath, the ACh-induced changes in electrophysiological parameters were significantly smaller than those observed in the presence of Ca2+. Both phorbol-12-myristate-13-acetate (PMA) and phorbol-12,13-dibutylate (PDBu), activators of protein kinase C (PKC), also inhibited the apical Na+ conductance. In the presence of PMA or PDBu in the bath, ACh did not show further inhibitory effect. 1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine, an inhibitor of PKC, partially attenuated the effect of ACh. These observations indicate that ACh inhibits the apical Na+ conductance partly by both increasing [Ca2+]i and activating PKC. Such an action of ACh may partially explain its natriuretic effect.
Takeda
M
M
Department of Pharmacology, Jichi Medical School, Tochigi, Japan.
Yoshitomi
K
K
Taniguchi
J
J
Imai
M
M
D000109:Acetylcholine / Q000494:pharmacology*; D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D018118:Chloride Channels / Q000187:drug effects; D007672:Kidney Cortex / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D011493:Protein Kinase C / Q000502:physiology; D011817:Rabbits; D011976:Receptors, Muscarinic / Q000502:physiology; D012964:Sodium / Q000378:metabolism*; D015222:Sodium Channels / Q000187:drug effects
D018118:Chloride Channels; D011976:Receptors, Muscarinic; D015222:Sodium Channels; D000584:Amiloride; D012964:Sodium; D011493:Protein Kinase C; D000109:Acetylcholine; D002118:Calcium