Positive and negative DC potential in the vestibular system of pigeons.

DC potential in the ampulla of pigeons was studied using a glass microelectrode. After the extirpation of the cochlear duct no change in the DC potential was found. A reduction of the negative DC potential due to anoxia (anoxia-sensitive negative potential, ASNP) was found in the ethacrynic acid (EA)-intoxicated ear, while this finding was minimal or absent in the ouabain-intoxicated ear. The perilymphatic perfusion with K(+)-substituted Ringer's solution resulted in a rapid reduction of the negativity due to EA or ouabain. These findings indicate that the positive DC potential in the ampulla seems to be produced by itself and K+ diffusion potential is the main source of negative DC potential. ASNP may be the unique potential in the EA-intoxicated ear in warm-blooded animals.

A new aspect in pathogenesis of experimental hydrops: role of calcium.

An imbalanced Ca++-homeostasis in the inner ear was demonstrated using an animal model for Menière's disease (MD). An increase of Ca++ concentration in the endolymph, as well as in some cells of the inner ear tissue, causes a rise of osmotic pressure and decrease of electric potential. Based on these results, we assume a new aspect in the pathophysiology of MD. It is proposed that the common denominator of MD, experimental endolymphatic hydrops (EEH), and space motion sickness (SMS) is primarily a shift of the inner ear Ca++ homeostasis towards a higher concentration of free Ca++ in the fluid compartments and adjacent intracellular spaces. It is postulated that an increase of Ca++ in this system might affect the transduction process and other functions associated with Ca++, such as turnover of otoconia.

Endolymph formation in the inner ear of pigeons.

The endolymphatic space of pigeons was studied by using double-barrelled electrodes with a potassium liquid ion exchanger. The K+ activity of the endolymph was 155 mM in the cochlea and 133 mM in the ampulla, respectively. Positive DC potential in the cochlea (+14.5 mV) was much lower than in guinea pigs (+80 mV) whereas in the ampulla of pigeons the DC potential (+7.4 mV) was 2 times higher than that of guinea pigs (+3.9 mV). General application of ethacrynic acid in pigeons induced a weak change in DC potential and no typical intercellular edema in the cochlea and ampulla. Local application of ethacrynic acid and ouabain in the cochlea and ampulla of pigeons induced a negative DC potential of between -30 and -40 mV. This negative DC potential was higher than the anoxia-induced negative potential. Short hypoxia during a drug-induced DC potential resulted in a decrease in DC potential above the diffusion potential. Below the diffusion potential additional hypoxia increased the DC potential independent of the cause of intoxication.

Cation transport in the ampulla of the semicircular canal and in the endolymphatic sac.

We examined the effects of anoxia and ethacrynic acid on the endolymphatic potential and cation activity in the superior ampulla of the guinea pig, using double-barrelled ion-exchanger microelectrodes. In normal guinea pigs the ampullar endolymphatic potential was + 3.9 +/- 1.2 mV (n = 32), the Cl- activity 130 +/- 4.6 mM (n = 9), and the Na+ activity 18.4 +/- 4.4 mM (n = 20). After anoxia, the ampullar DC potential decreased rapidly and reversed its polarity within 5 min. It then decreased gradually for 60 min and increased afterwards to approximately zero. K+ activity decreased gradually after a latency of 10 min, whereas Na+ activity increased. During the gradual decrease of a negative ampullar endolymphatic potential, an increase in Na+ activity was observed. Thirty minutes after the intravenous injection of ethacrynic acid (100 mg/kg), the potential began to decrease, changed to a negative polarity, and approached a maximum negative level 100 min after the injection. The decrease in K+ activity corresponded to the reduction of potential whereas Na+ activity remained unchanged. The DC potential of the endolymphatic sac in normal guinea pigs was + 14.7 +/- 5.1 mV (n = 17). The Na+ concentration was 103.3 +/- 14.7 mM (n = 14) and the K+ concentration was 11.6 +/- 0.8 mM (n = 4). After anoxia, the DC potential decreased rapidly and approached 0 mV within 8 min. No negative potential could be observed. The Na+ concentration began to increase 2 min after anoxia and reached the extracellular Na+ concentration about 30 min later.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium transport in the endolymphatic space of cochlea and vestibular organ.

Ca++ concentrations and d.c. potential within the endolymphatic space of the cochlear duct and the semicircular canal following acute anoxia or ethacrynic acid intoxication (100 mg/kg i.v.) were measured by means of double-barrelled microelectrodes. Ionic calcium content and d.c. potential were found to change in a roughly biphasic fashion after either intervention. The maximal increase in Ca++ concentration coincided with the decline in the d.c. potential, which after a rapid decline finally reached and maintained negative voltages. This phenomenon was more pronounced in the cochlear part than in the semicircular canal. A model of calcium homeostasis is proposed in an attempt to reconcile the data presented with earlier evidence.

[Effect of aminoglycosides on experimentally induced endolymphatic hydrops]. / Zur Wirkung von Aminoglykosiden auf den experimentell erzeugten endolymphatischen Hydrops.

Gentamycin or kanamycin have no effect on endolymph formation in experimental induced endolymphatic hydrops. The increase of endolymphatic volume after obliteration of endolymphatic duct and sac is not influenced by aminoglycosides as well as the decrease of DC-potential and the increase of sodium-activity in endolymphatic hydrops. The way of action of intratympanal injected gentamycin seems to be in a partial chemical induced labyrinthectomy.

Calcium transport in the endolymphatic sac.

Ca++ activity and DC potential were measured in vivo in the endolymphatic sac (ES) of guinea pigs by means of double-barrelled ion-sensitive microelectrodes. We found a positive DC potential of 14 mV and a Ca++ activity of 4.7 X 10(-4) M. Anoxia induced a decrease in the DC potential and an increase in Ca++ activity; however, no negative DC potential was measured during permanent anoxia. The Ca++ activity measured was in agreement with the Ca++ value calculated with the Nernst equation, assuming a positive DC potential. On the basis of these data, it was suggested that the Ca++ in the ES is in electrochemical equilibrium with the surrounding fluid and no active Ca++ transport is necessary in the ES of guinea pigs.

Changes in Ca++ activity and DC potential in experimentally induced endolymphatic hydrops.

We found changes in Ca++ activity and DC potential during the development of experimentally induced endolymphatic hydrops in guinea pigs. These findings indicate that there is some correlation between Ca++ activity and DC potential in the cochlear endolymph.

Ca++ activity in the endolymphatic space.

We measured Ca++ activity in the different parts of the endolymphatic space by using a double-barrelled electrode with calcium liquid ionic exchanger. In the region of the endolymphatic sac, Ca++ activity (4.7 X 10(-4) M) was much higher than in the cochlear duct (2.7 X 10(-5) M) and semicircular canal (2.6 X 10(-4) M). These findings suggest that Ca++ may also have a significant role in abnormal states.

Adrenergic and peptidergic innervation of cochlear blood vessels.

Guinea pig cochlear blood vessels were investigated with regard to their supply of adrenergic and peptidergic nerve fibers. Using the glyoxylic acid histofluorescence technique, numerous adrenergic fibers were seen around the labyrinthine artery, whereas the spiral modiolar artery contained only few such fibers. Immunocytochemistry revealed nerve fibers containing immunoreactive avian pancreatic polypeptide, vasoactive intestinal peptide, substance P, or gastrin-releasing peptide around the labyrinthine and spiral modiolar arteries. Adrenergic or peptidergic nerve fibers were not seen around the blood vessels of the stria vascularis. Upon removal of the superior cervical ganglion, adrenergic fibers disappeared and fibers displaying avian pancreatic polypeptide immunoreactivity were reduced in number. These data suggest co-occurrence of catecholamines and immunoreactive avian pancreatic polypeptide in a population of adrenergic nerves.