Effects of extracellular sodium, quinidine, and ryanodine on slow response excitability in rabbit atrial trabeculae.
1. We investigated Na(+)-Ca2+ exchange and the involvement of the sarcoplasmic reticulum in frequency-dependent slow response excitability enhancement in rabbit atrial trabeculae. 2. Slow responses were induced in a modified Tyrode solution containing high K+ and Ba2+ and conventional electrophysiological techniques were used for stimulating and recording membrane potentials. 3. Under these conditions, the frequency-dependence of slow response excitability can be demonstrated with excitability enhancement as stimulation frequency is increased (0.25 to 1.0 Hz). 4. The frequency-dependent excitability enhancement depends on external Na+, increasing in high-[Na+]o (173.8 mM) and decreasing in low-[Na+]o (103.8 mM) media. 5. Quinidine (10 microM) and ryanodine (10 microM) decrease frequency-dependent slow response excitability enhancement. 6. These results indicate that the Na(+)-Ca2+ exchange might have an important role in frequency-dependent excitability enhancement of slow responses. Moreover, we suggest that the control of internal Ca2+ by the sarcoplasmic reticulum might have an additional role in regulating the excitability enhancement process in depolarized atrial trabeculae.
Nascimento
J H
JH
Instituto de Biofisica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Brasil.
Masuda
M O
MO
Cukierman
S
S
D000818:Animals; D016275:Atrial Function; D002118:Calcium / Q000378:metabolism; D004558:Electric Stimulation; D004594:Electrophysiology; D005110:Extracellular Space / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D011802:Quinidine / Q000494:pharmacology; D011817:Rabbits; D012433:Ryanodine / Q000494:pharmacology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
D012433:Ryanodine; D012964:Sodium; D011802:Quinidine; D002118:Calcium