Nucleoside influx and efflux in guinea-pig ventricular myocytes. Inhibition by analogues of lidoflazine.
Adenosine influx and formycin B influx and efflux were characterized in guinea-pig ventricular myocytes at 22 degrees. Transport by both modes was saturable and inhibited by nitrobenzylthioinosine (NBMPR), indicating the presence of an equilibrative NBMPR-sensitive nucleoside transporter in the cardiomyocytes. The kinetic constants for influx and efflux of formycin B, a non-metabolized nucleoside, were similar, suggesting that the nucleoside transporter exhibits symmetrical kinetics (apparent Km 490 +/- 160 and 700 +/- 140 microM; Vmax 6.5 +/- 1.7 and 3.5 +/- 0.3 nmol/10(6) cells per min for influx and efflux, respectively). No evidence was found of either NBMPR-insensitive equilibrative nucleoside transport or sodium-dependent concentrative nucleoside transport. Inhibition of adenosine influx (apparent Km100 +/- 33 microM), by lidoflazine and the analogues mioflazine, soluflazine and R73-335, gave average Ki values of 730, 100, 64 and 2.9 nM, respectively. These compounds also inhibited formycin B efflux with a similar potency to that of adenosine influx. NBMPR-sensitive nucleoside transport was associated with high affinity binding of NBMPR (apparent Kd approximately 1 nM; 9.6 x 10(5) sites/cell). Specific binding of NBMPR was also inhibited by lidoflazine and its analogues. Mioflazine and soluflazine were 20-30-fold more potent at inhibiting NBMPR-sensitive nucleoside influx in guinea-pig erythrocytes than ventricular myocytes, indicating that the potency of some of the compounds studied is tissue dependent.
Conant
A R
AR
Research School of Biosciences, University of Kent, Canterbury, U.K.
Jarvis
S M
SM
D000241:Adenosine / Q000378:metabolism*; D000345:Affinity Labels; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D005573:Formycins / Q000378:metabolism; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008013:Lidoflazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D013868:Thioinosine / Q000031:analogs & derivatives / Q000494:pharmacology
D000345:Affinity Labels; D005573:Formycins; C034561:formycin B; D013868:Thioinosine; C001789:4-nitrobenzylthioinosine; D008013:Lidoflazine; D000241:Adenosine