AJP - Heart and Circulatory Physiology, Vol 261, Issue 5 1437-H1442, Copyright © 1991 by American Physiological Society
gamma-Aminobutyric acid is a neuromodulator in sinus node of guinea pig heart
S. Matsuyama, N. Saito, K. Taniyama and C. Tanaka
Department of Pharmacology, Kobe University School of Medicine, Japan.
A possible neurotransmitter role for gamma-aminobutyric acid (GABA) in the
sinus node of guinea pig heart was examined. Among right atrium, left
atrium, right ventricle, left ventricle, and sinus node, the highest amount
of the endogenous GABA was found in the sinus node (1,240.6 +/- 120.8
nmol/g protein). The neuronal uptake of [3H]GABA was also the highest in
the sinus node and kinetic analysis of the [3H]GABA uptake system in the
sinus node showed one saturable component (Km = 17.3 microM, Vmax = 2.18
nmol.g protein-1.10 min-1). Autoradiography of [3H]GABA demonstrated heavy
labeling of [3H]GABA in the nonmyelinated nerve fibers within the sinus
node compared with findings in the atrial muscle. Electrical transmural
stimulation evoked a Ca(2+)-dependent tetrodotoxin-sensitive release of
[3H]GABA from the isolated sinus node preloaded with [3H]GABA in the
presence of beta-alanine, thereby indicating that the [3H]GABA in the nerve
is released from nerve terminals following electrical stimulation. These
results provide evidence for the neuromodulator role of GABA in the sinus
node of the guinea pig.
