Electrical properties of smooth muscle cell membrane in renal pelvis of rabbits

Abstract

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.