Membrane properties and the excitatory junction potentials in smooth muscle cells of cochlear spiral modiolar artery in guinea pigs

Blood circulation changes in the inner ear play an important role in many p hysiological and pathological conditions of hearing function. The spiral mo diolar artery (SMA) is the terminal artery to the cochlea. It was surrounde d with nerve fibers immunostained by an antibody for tyrosine hydroxylase. By using intracellular recording techniques on the acutely isolated SMA, me mbrane properties of the smooth muscle cells and the neuromuscular transmis sion in this preparation were investigated. With minimum tension and normal extracellular K+ concentration (5 mM), the majority of muscle cells showed a resting potential near - 80 mV and an input resistance of about 8 M Omeg a. V/I plot showed an inward rectification in these cells. Barium (50-500 m u M) caused strong depolarization and an increase in input resistance. Tran smural electrical stimulation evoked stimulation intensity-dependent depola rizations (2-31 mV) following a short latency (similar to 20 ms). The evoke d potential by a low intensity stimulus was completely blocked by I CIM tet rodotoxin. The potential and a depolarization induced by norepinephrine (10 mu M) was usually partially (40-90%) blocked by a-receptor antagonists pra zosin and/or idazoxan with concentrations up to 1 mu M. Action potentials w ere observed when the depolarization was more than -40 mV. It is concluded that SMA smooth muscle cells, similar to those in other brain small arterie s, highly express inward rectifying potassium channels; the cells receive c atecholaminergic innervation, and stimulation of the nerves elicited an exc itatory junction potential that is partially mediated by adrenergic recepto rs. (C) 1999 Elsevier Science B.V. All rights reserved.