Modulation of L-type Ca2+ current by extracellular ATP in ferret isolated right ventricular myocytes.
1. The effects of extracellular adenosine triphosphate (ATP) on the basal L-type Ca2+ current (ICa) were investigated in ferret isolated right ventricular myocytes using the gigaohm seal voltage clamp in the whole-cell and cell-attached configurations. 2. Micromolar levels of extracellular ATP reversibly inhibited ICa in a concentration-dependent manner, without any significant changes in the voltage dependence of either the peak ICa I-V relationship or steady-state activation curve. 3. In contrast, micromolar levels of extracellular ATP did significantly alter the inactivation characteristics of ICa. Ten micromolar ATP: (i) increased the degree of steady-state inactivation of ICa; (ii) altered the time constants of ICa inactivation at 0 mV; and (iii) decreased the time constant of ICa recovery from inactivation at -70 mV. 4. The inhibitory effect of ATP on ICa was not blocked by atropine, a muscarinic cholinergic receptor antagonist, or CPDPX (8-cyclopentyl-3,4-dipropylxanthine), an A1 adenosine receptor antagonist. In contrast, the inhibitory effect of 10 microM ATP could be nearly completely antagonized by 100 microM suramin, a purinergic P2 receptor antagonist. 5. The potency order of ATP analogues in inhibiting ICa was 2-methyl-thio-ATP > ATP > alpha,beta-methylene-ATP, indicating involvement of a P2Y-type ATP receptor. 6. Pretreatment of cells with pertussis toxin (PTX) did not prevent the ATP-induced decrease in ICa. However, (i) ATP produced an irreversible decrease of ICa in the presence of intracellular GTP gamma S, and (ii) the inhibitory effect was significantly attenuated in the presence of intracellular GDP beta S, indicating the involvement of a PTX-insensitive G protein in the P2Y receptor-coupling process. 7. Neither (i) replacing extracellular Ca2+ with 1 mM Ba2+, nor (ii) intracellular perfusion of 10 mM BAPTA for at least 30 min attenuated the inhibitory effect of ATP on the current through Ca2+ channels, suggesting that the inhibitory effect was not obligatorily dependent upon influx of Ca2+ or changes in [Ca2+]i. 8. Ensemble-average current behaviour constructed from cell-attached patch recordings of single L-type Ca2+ channels (110 mM BaCl2) demonstrated that when 10 microM ATP was added to the superfusate on the outside of the patch electrode the inhibition of ICa was still observed, providing evidence for the involvement of intracellular diffusible second messenger(s).(ABSTRACT TRUNCATED AT 400 WORDS)
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Department of Pharmacology, Duke University Medical Center, Durham, NC 27710.
Campbell
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Strauss
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D000241:Adenosine / Q000378:metabolism / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004594:Electrophysiology; D005289:Ferrets; D019204:GTP-Binding Proteins / Q000378:metabolism; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D017136:Ion Transport / Q000187:drug effects; D008297:Male; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D037342:Pertussis Toxin; D011493:Protein Kinase C / Q000378:metabolism; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000378:metabolism; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology; D013498:Suramin / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D007295:Inositol Phosphates; D018047:Receptors, Purinergic P1; D010566:Virulence Factors, Bordetella; D013498:Suramin; D000255:Adenosine Triphosphate; D037342:Pertussis Toxin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D000241:Adenosine; D002118:Calcium