Purinoceptor-stimulated phosphoinositide hydrolysis in Madin-Darby canine kidney (MDCK) cells.
Extracellular nucleotides, acting through P2-purinoceptors, have been implicated in the regulation of ion transport in epithelia, including Madin-Darby canine kidney (MDCK) cells. In this study, experiments were conducted to characterize the P2-purinoceptor subtype on MDCK cells responsible for stimulating inositol phosphate (IP) accumulation using a range of nucleotide analogues. In Ca2+- and Mg2+-free Krebs-Henseleit solution (KHS), ATP, UTP, and ATPgammaS caused an increase in IP accumulation as a function of concentration with comparable kinetics. The order of potency for the nucleotide analogues was UTP = ATPgammaS > ATP = 2-chloro ATP (Cl-ATP) >> alpha,beta-methylene ATP (alpha,beta-MeATP) = 2-methylthio ATP (2MeSATP). Selective agonists for P1-, P2X- and P2Y-purinoceptors, such as N6-cyclopentyl adenosine, AMP, alpha,beta-MeATP, and 2MeSATP, had little effect. Stimulation of MDCK cells with maximally effective concentrations of ATP and UTP showed no additive effect and furthermore, ATP, UTP, and ATPgammaS induced cross-desensitization of the IP response, suggesting that ATP and UTP act upon a common nucleotide receptor, i.e. a P2U-purinoceptor. In Ca2+- and Mg2+-containing KHS, the concentration-response curves of ATP, UTP, and ATPgammaS were shifted to the right of those obtained in Ca2+- and Mg2+-free buffer, and asymptotic maxima were not reached, indicating that ATP4- and not MgATP2- or CaATP2- was the active agonist. Pretreatment of MDCK cells with pertussis toxin (PTX) inhibited ATP- and UTP-induced IP accumulation in a concentration-dependent fashion but did not completely abolish the IP accumulation, indicating that a PTX-sensitive G protein was partially involved in the IP response. In conclusion, ATP- and UTP-stimulated IP accumulation in MDCK cells appears to be mediated through the activation of P2U-purinoceptors coupled to a G protein that is partially sensitive to PTX. A form of nucleotide uncomplexed with divalent ions such as ATP4- seems to be the preferential agonist form for the purinoceptors on MDCK cells.
Yang
C M
CM
Department of Pharmacology, Chang Gung College of Medicine and Technology, Tao-Yuan, Taiwan.
Tsai
Y J
YJ
Pan
S L
SL
Tsai
C T
CT
Wu
W B
WB
Chiu
C T
CT
Luo
S F
SF
Ou
J T
JT
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D004285:Dogs; D006868:Hydrolysis; D066298:In Vitro Techniques; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000378:metabolism*; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2 / Q000145:classification / Q000502:physiology*; D014544:Uridine Triphosphate / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D010716:Phosphatidylinositols; D058910:Purinergic P2 Receptor Agonists; D018048:Receptors, Purinergic P2; D010566:Virulence Factors, Bordetella; C022571:adenosine 5'-O-(3-thiotriphosphate); D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D014544:Uridine Triphosphate