Multiple regulation by external ATP of nifedipine-insensitive, high voltage-activated Ca(2+) current in guinea-pig mesenteric terminal arteriole.
We investigated the receptor-mediated regulation of nifedipine-insensitive, high voltage-activated Ca(2+) currents in guinea-pig terminal mesenteric arterioles (I(mVDCC)) using the whole-cell clamp technique. Screening of various vasoactive substances revealed that ATP, histamine and substance P exert modulatory effects on I(mVDCC). The effects of ATP on I(mVDCC) after complete P2X receptor desensitization exhibited a complex concentration dependence. With 5 mM Ba(2+), ATP potentiated I(mVDCC) at low concentrations (approximately 1-100 microM), but inhibited it at higher concentrations (>100 microM). The potentiating effects of ATP were abolished by suramin (100 microM) and PPADS (10 microM) and by intracellular application of GDPbetaS (500 microM), whereas a substantial part of I(mVDCC) inhibition by milimolar concentrations of ATP remained unaffected; due probably to its divalent cation chelating actions. In divalent cation-free solution, I(mVDCC) was enlarged and underwent biphasic effects by ATPgammaS and ADP, while 2-methylthio ATP (2MeSATP) exerted only inhibition, and pyrimidines such as UTP and UDP were ineffective. ATP-induced I(mVDCC) potentiation was selectively inhibited by anti-Galpha(s) antibodies or protein kinase A (PKA) inhibitory peptides and mimicked by dibutyryl cAMP. In contrast, ATP-induced inhibition was selectively inhibited by Galpha(q/11) antibodies or protein kinase C (PKC) inhibitory peptides and mimicked by PDBu. Pretreatment with pertussis toxin was ineffective. The apparent efficacy for I(mVDCC) potentiation with PKC inhibitors was: ATPgammaS > ATP>/=ADP and for inhibition with PKA inhibitors was: 2MeSATP > ATPgammaS > ATP > ADP. Neither I(mVDCC) potentiation nor inhibition showed voltage dependence. These results suggest that I(mVDCC) is multi-phasically regulated by external ATP via P2Y(11)-resembling receptor/G(s)/PKA pathway, P2Y(1)-like receptor/G(q/11)/PKC pathway, and metal chelation.
Morita
Hiromitsu
H
Department of Pharmacology, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan.
Sharada
Thapaliya
T
Takewaki
Tadashi
T
Ito
Yushi
Y
Inoue
Ryuji
R
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001160:Arterioles / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D005260:Female; D019204:GTP-Binding Proteins / Q000502:physiology; D006168:Guinea Pigs; D007700:Kinetics; D008297:Male; D009543:Nifedipine / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D011493:Protein Kinase C / Q000502:physiology; D018048:Receptors, Purinergic P2 / Q000502:physiology; D013152:Splanchnic Circulation / Q000187:drug effects* / Q000502:physiology*
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018048:Receptors, Purinergic P2; D000255:Adenosine Triphosphate; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D009543:Nifedipine