Increased sensitivity of neonate atrial myocytes to adenosine A1 receptor stimulation in regulation of the L-type Ca2+ current.
Adenosine has cardioprotective effects against ischemia, and newborn hearts show high resistance to ischemia. The effects of purinoceptor stimulation by adenosine and ATP on the L-type Ca2+ current (ICa) were examined in atrial cells from neonate and adult rabbits. ICa was measured by the membrane-perforated patch method. Adenosine inhibited the isoproterenol-stimulated ICa more potently in neonate cells than in adult cells. The high sensitivity of neonate myocytes to adenosine was accompanied not only by an increased maximum response but also by a lower IC50 concentration. ATP also inhibited isoproterenol-stimulated ICa. The effect of ATP on neonate cells was stronger than that on adult cells at high concentrations (greater than or = 100 microM). The effect of adenosine was antagonized by an A1 adenosine receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX). DPCPX or an ecto-5'-nucleosidase inhibitor (alpha,beta-methylene-ADP) blocked most (approximately 60%) of the effect of ATP (30 microM), and co-addition of DPCPX and suramin (P2 receptor blocker) abolished the effect of ATP. Suramin alone did not reduce the effect of ATP significantly in neonate cells. Both the effects of adenosine and ATP were eliminated by pre-treatment with pertussis toxin or by superfusion with forskolin plus 3-isobutyl-1-methylxanthine (IBMX). Inhibitors of the nitric oxide-cyclic GMP pathway did not affect the adenosine inhibition of ICa. In summary, neonatal myocardial cells are highly sensitive to adenosine A1 receptor stimulation. ATP stimulates both the adenosine A1 and P2 receptors. Adenosine A1 receptor stimulation, as a result of hydrolysis of ATP, predominantly mediates the effect of ATP, and the role of P2 receptors in the ATP inhibition of ICa is relatively small in neonate cells. The high sensitivity to adenosine may contribute to the ischemic tolerance of newborn hearts.
Suto
F
F
Department of Pediatrics, Children's Research Hospital, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji, Kyoto 602-0841, Kamigyo-ku, Japan.
Habuchi
Y
Y
Yamamoto
T
T
Tanaka
H
H
Hamaoka
K
K
D000241:Adenosine / Q000494:pharmacology*; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects* / Q000502:physiology; D006325:Heart Atria / Q000166:cytology / Q000187:drug effects; D011817:Rabbits; D018047:Receptors, Purinergic P1 / Q000187:drug effects* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D000889:Anti-Arrhythmia Agents; D020746:Calcium Channels, L-Type; D018047:Receptors, Purinergic P1; D000255:Adenosine Triphosphate; D000241:Adenosine