AJP - Renal Physiology, Vol 259, Issue 6 888-F894, Copyright © 1990 by American Physiological Society
Electrical properties of smooth muscle cell membrane in renal pelvis of rabbits
N. Seki and H. Suzuki
Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Intracellular recordings were made to study the electrical properties of
smooth muscle cells in the rabbit renal pelvis. The muscle cells exhibited
spontaneous oscillation in the membrane potential (slow wave). The slow
waves were regular and were resistant to tetrodotoxin and sympathomimetic
or parasympathomimetic antagonists, findings indicative of myogenic
activity. The membrane was depolarized by an increase in extracellular
concentration of K+ ([K+]o), decrease in [Na+]o, inhibition of the
electrogenic Na(+)-K+ pump by ouabain or K(+)-free solution, and the
application of norepinephrine (NE, greater than 10(-6) M). The maximum
slope of the membrane depolarization produced by a 10-fold increase in
[K+]o was approximately 48 mV. Reductions in [Ca2+]o inhibited the
generation of slow waves with no marked change in the membrane potential.
Depolarizations produced by any given method increased the frequency and
decreased the amplitude of the slow wave, and NE had the most potent
accelerating action on the frequency. Hyperpolarization of the membrane by
1-5 mV with extracellularly applied current stimuli reduced the frequency,
and a strong hyperpolarization (greater than 5 mV) blocked the generation
of slow waves. Electrophysiological properties of the slow waves obtained
with tissues of the renal pelvis and intestinal smooth muscles were
compared.
