[Different sensitivity of sinus node and atrioventricular node to adenosine triphosphate].
We showed that higher concentration of adenosine 5'-triphosphate (ATP) was required to prolong the spontaneous cycle length of the sinus node (SN) than that required to prolong the spontaneous cycle length of the atrioventricular node (AVN). Spontaneously beating preparations of SN and AVN of rabbit (n = 8) were superfused with Tyrode solution containing 10(-8)-10(-3)M ATP, and action potential was recorded. The negative chronotropic action of ATP was dependent on the concentration. The required concentration of ATP to prolong spontaneous cycle length significantly (p less than 0.01) was 10(-5)M in SN and 10(-6)M in AVN, respectively. At concentrations higher than 10(-6)M, the degree of prolongation was greater in AVN than in SN (p less than 0.01). 10(-7)M dipyridamole enhanced this effect of ATP, while 10(-4)M theophylline reduced it. Action potential duration of 50% repolarization was not changed significantly in either SN or AVN at concentrations up to 10(-3)M. Maximum diastolic potential (MDP) was hyperpolarized from 10(-8)M to 10(-4) M. Hyperpolarization of MDP induced by ATP was greater in AVN than in SN but it was not statistically significant. MDP was depolarized by 10(-3) M ATP in both SN and AVN. The maximum velocity of depolarization was slightly larger in both SN and AVN as the concentration of ATP was increased in the perfusate. However, it was not statistically significant. 10(-3) M ATP decreased the maximum velocity of depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)
Shirayama
T
T
Second Department of Medicine, Kyoto Prefectural University of Medicine.
Inoue
D
D
Omori
I
I
Tatsumi
T
T
Tatsukawa
H
H
Asayama
J
J
Katsume
H
H
Nakagawa
M
M
Tsuji
Y
Y
D000200:Action Potentials / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001283:Atrioventricular Node / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D006329:Heart Conduction System / Q000187:drug effects*; D066298:In Vitro Techniques; D011817:Rabbits; D012849:Sinoatrial Node / Q000187:drug effects*
D000255:Adenosine Triphosphate