ATP activates cationic currents and modulates the calcium current through GTP‐binding protein in rabbit portal vein.

Abstract

SUMMARY1. Effects of adenosine 5'-triphosphate (ATP) on ionic currents of dispersed smooth muscle cells of the rabbit portal vein were investigated using the voltageclamp procedure.2. ATP (> 300 ,M) produced transient and maintained inward currents. The former was inactivated within a few seconds, but the latter lasted more than several minutes. The transient but not the maintained current was blocked by pre-treatment with a,fl-methylene adenosine 5'-triphosphate (AMP-CPP). The amplitude of the latter was increased by ATP in a concentration-dependent manner. The following investigations were made on the ionic mechanism of the ATP-induced maintained inward current.3. In 2-5 mM-Ca2l-containing tetraethylammonium chloride (TEA-Cl) solution (2-5 mM-Ca2+-TEA+ solution), the reversal potential for the ATP-induced inward current was close to the Cl-equilibrium potential, and in 140 mM-Na' (nominally Ca2+-free or 0 3 mM-EGTA-containing) solution, the reversal potential was coincident with the Na+ equilibrium potential.4. In 2-5 mm-Ca2+-TEA+ solution but not in 140 mM-Na+ solution and in physiological salt solution (PSS), niflumic acid (10 pSM), a Cl-channel blocker, andCl--deficient perfusate in the pipette markedly inhibited the ATP-induced inward current. These results imply that in 2-5 mm-Ca2+-TEA+ solution the ATP-activated ion channel may admit Ca2+ which then accelerates the Ca2+-dependent Cl-current, but in 140 mM-Na+ solution and in PSS this channel may admit only Na+. 5. Intracellular perfusion of guanosine 5'-O-(3-thio triphosphate (GTPyS) did not provoke the current, but significantly increased the amplitude of the ATP-induced inward current in 2-5 mM-Ca2+-TEA+, 140 mM-Na+ and 2-5 mm-Ba2+-containing TEA+ (2-5 mM-Ba2+-TEA+) solutions. On the other hand, intracellular perfusion of guanosine 5'-O-(2-thiodiphosphate) (GDPpS) reduced the amplitude of the ATPinduced inward current in the above solutions. Z. XIONG, K. KITAMURA AND H. KURIYAMA inhibition was partly prevented by application of 20 mM-EGTA in the pipette. In 140 mM-Na' solution (with 0 3 mM-EGTA), ATP (3 mM) slightly inhibited the amplitude of the voltage-dependent inward current which was generated by permeation of the Na+ (Na+ current) through the voltage-dependent Ca2+ channel.7. In 140 mM-Na' solution (with 0-3 mM-EGTA), 2-5 mM-Ba2+-TEA+ solution and PSS, neither GTPyS nor GDP,fS in the pipette modified the amplitude of the voltage-dependent inward current. However, GTPyS pronounced but GDPflS prevented the inhibition of the voltage-dependent inward current induced by ATP. 8. Pertussis toxin (300 ng/ml) inhibited the ATP-induced inward current, and attenuated the ATP-induced inhibition of the voltage-dependent inward current in 2-5 mm-Ba2+-TEA' solution and PSS.9. These results indicate that ATP activates two different receptor-operated currents: AMP-CPP-sensitive (transient component) and -resistant (maintained component) currents. The latter appears to permeate only Na+ in PSS. The results also suggest that ATP transiently activates and then inhib...

Effects of excitatory neurotransmitters on Ca2+ channel current in smooth muscle cells isolated from guinea‐pig urinary bladder

“…The persistent enhancement of the Ca2" channel current and the lack of effect of desensitization by a,-methylene ATP suggest that this effect of ATP is not through purinoceptor stimulation, but probably through chelation of extracellular Mg2`(divalent cation block of Ca2" channel current carried by monovalent cations: Fukushima & Hagiwara, 1985). In rabbit portal vein, a similar phenomenon has been reported (Xiong et al, 1991). Figure 4 shows the effect of purinoceptor stimulation during a large depolarization.…”

Purinergic Signaling and Blood Vessels in Health and Disease

“…ATP activates cation currents in the rabbit portal vein (Xiong et al, 1991;Pacaud et al, 1994), consistent with P2X receptor activation (Orre et al, 1996). The P2 receptor mediating contraction of the longitudinal muscle of the rat portal vein is also the P2X receptor subtype , and P2X 1 receptors have been identified on rat portal vein myocytes (Orre et al, 1996;Mironneau et al, 2001).…”

Action of angiotensin II, 5‐hydroxytryptamine and adenosine triphosphate on ionic currents in single ear artery cells of the rabbit

“…G proteins are known to modulate the activity of a number of ion channels (Clapham, 1994) and acetylcholine has been reported to open a cation channel in guinea-pig ileal smooth muscle (Inoue & Isenberg, 1990a;Komori et al, 1992) through a G protein-dependent mechanism. Intracellular dialysis of rabbit portal vein cells with the non-hydrolysable analogue of GDP, GDP-,B-S has been reported to reduce ATP-induced cation currents (Xiong et al, 1991), and Oike and colleagues (1993) reported that a pertussis toxin-sensitive G protein participated in the activation of a cation current by phorbol 12,13-dibutyrate, a protein kinase C activator. Further studies will be necessary to explore the possibility that G proteins also mediate the effects of AIL, 5-HT and ATP on channels in vascular smooth muscle cells.…”