Intracellular potassium activity in rabbit sinoatrial node. Evaluation during spontaneous activity and arrest.

Effects of block of the rapid delayed rectifier K+current ( I K,r) by E-4031 on the electrical activity of small ball-like tissue preparations from different regions of the rabbit sinoatrial node were measured. The effects of partial block of I K,r by 0.1 μM E-4031 varied in different regions of the node. In tissue from the center of the node spontaneous activity was generally abolished, whereas in tissue from the periphery spontaneous activity persisted, although the action potential was prolonged, the maximum diastolic potential was decreased, and the spontaneous activity slowed. After partial block of I K,r, the electrical activity of peripheral tissue was more like that of central tissue under normal conditions. One possible explanation of these findings is that the density of I K,r is greater in the periphery of the node; this would explain the greater resistance of peripheral tissue to I K,r block and help explain why, under normal conditions, the maximum diastolic potential is more negative, the action potential is shorter, and pacemaking is faster in the periphery.

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Acetylcholine inhibition in rabbit sinoatrial node is prevented by pertussis toxin

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y89-083 ◽

1989 ◽

Vol 67 (5) ◽

pp. 522-525 ◽

Cited By ~ 2

Author(s):

Paschalis-Adam Molyvdas ◽

Nick Sperelakis

Keyword(s):

Spontaneous Activity ◽

Pertussis Toxin ◽

Culture Medium ◽

Sinoatrial Node ◽

Sa Node ◽

Naturally Occurring ◽

Low Concentrations ◽

Organ Culture Medium ◽

Rabbit Sinoatrial Node ◽

Slow Action Potentials

The effects of acetylcholine (ACh) were examined on the naturally occurring slow action potentials (APs) of the isolated, organ-cultured, spontaneously beating sinoatrial (SA) node of the rabbit, in the presence or absence of pertussis toxin. The sensitivity of the SA-node preparations to ACh was not altered after 24 h incubation in organ culture medium. Activation of the muscarinic receptor hyperpolarized the cells and reduced the frequency of spontaneous activity at low concentrations (1 × 10−6 and 3 × 10−6 M), and completely abolished automaticity at higher concentrations (1 × 10−5 M). However, stimulated activity was maintained. Increased concentrations (1 × 10−4 M) of ACh completely abolished excitability. When the SA-node preparations were cultured in the presence of 0.5 μg/mL pertussis toxin, concentrations of ACh as high as 1 × 10−4 M had no effect on the AP parameters and frequency of spontaneous activity. The results indicate that inactivation of G proteins by pertussis toxin caused inhibition of the ACh effects on the automaticity of the SA node. In addition, the blocking effect of ACh to the naturally occurring slow APs was also inhibited by pertussis toxin. We conclude that in the rabbit SA node, the effects of ACh on automaticity and on the slow channels are mediated by G protein.Key words: sinoatrial node, acetylcholine, pertussis toxin.

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