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At least 1,117 records · Page 62Linked to original sources
PubMed1989

Volume receptors in guinea pig labyrinth: relevance with respect to ADH and Na control.

We tested the hypothesis that changes in extracellular fluid volume are reflected by pressure changes within structures of the inner ear and that through neural pathways, a control mechanism exerts an influence on antidiuretic hormone (ADH) release and Na excretion. The study was performed on 35 guinea pigs. In protocol 1, 13 animals were studied before and after decompression of the inner ear by bilateral fluid withdrawal in an experimental setting of sustained isotonic expansion that kept the osmoreceptor partially activated and the intrathoracic volume receptors suppressed. A group of six sham-operated animals served as control. In protocol 2, nine animals were studied before and after a unilateral rise in their inner ear pressure during slightly hypertonic low-rate infusions that kept the osmoreceptor and thoracic volume receptors stimulated. A group of seven sham-operated guinea pigs served as controls. Decompression of the inner ear was attended by a rise in plasma ADH from 11.9 +/- 2.4 to 29.1 +/- 6.9 pg/ml, in urine osmolality (Uosmol) from 470 +/- 48 to 712 +/- 46 mosmol/kg (P less than 0.001), and a fall in urine flow rate (V) from 184 +/- 47 to 71 +/- 11 microliters/min (P less than 0.01), whereas plasma Na (PNa) and osmolality (Posmol) did not change. During inner ear hypertension, plasma ADH fell from 25.6 +/- 3.9 to 18.4 +/- 3.1, Uosmol from 829 +/- 58 to 627 +/- 43 (P less than 0.001), and V rose from 51 +/- 11 to 130 +/- 23 (P less than 0.001), whereas glomerular filtration rate, PNa, and Posmol did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Electrophysiological properties of vestibular sensory and supporting cells in the labyrinth slice before and during regeneration.

The whole cell patch-clamp technique in combination with the slice preparation was used to investigate the electrophysiological properties of pigeon semicircular canal sensory and supporting cells. These properties were also characterized in regenerating neuroepithelia of pigeons preinjected with streptomycin to kill the hair cells. Type II hair cells from each of the three semicircular canals showed similar, topographically related patterns of passive and active membrane properties. Hair cells located in the peripheral regions (zone I, near the planum semilunatum) had less negative resting potentials [0-current voltage in current-clamp mode (Vz) = -62.8 +/- 8.7 mV, mean +/- SD; n = 13] and smaller membrane capacitances (Cm = 5.0 +/- 0.9 pF, n = 14) than cells of the intermediate (zone II; Vz = -79.3 +/- 7.5 mV, n = 3; Cm = 5.9 +/- 1.2 pF, n = 4) and central (zone III; Vz = -68.0 +/- 9.6 mV, n = 17; Cm = 7.1 +/- 1.5 pF, n = 18) regions. In peripheral hair cells, ionic currents were dominated by a rapidly activating/inactivating outward K+ current, presumably an A-type K+ current (IKA). Little or no inwardly rectifying current was present in these cells. Conversely, ionic currents of central hair cells were dominated by a slowly activating/inactivating outward K+ current resembling a delayed rectifier K+ current (IKD). Moreover, an inward rectifying current at voltages negative to -80 mV was present in all central cells. This current was composed of two components: a slowly activating, noninactivating component (Ih), described in photoreceptors and saccular hair cells, and a faster-activating, partially inactivating component (IK1) also described in saccular hair cells in some species. Ih and IK1 were sometimes independently expressed by hair cells. Hair cells located in the intermediate region (zone II) had ionic currents more similar to those of central hair cells than peripheral hair cells. Outward currents in intermediate hair cells activated only slightly more quickly than those of the cells of the central region, but much more slowly than those of the peripheral cells. Additionally, intermediate hair cells, like central hair cells, always expressed an inward rectifying current. The regional distribution of outward rectifying potassium conductances resulted in macroscopic currents differing in peak-to-steady state ratio. We quantified this by measuring the peak (Gp) and steady-state (Gs) slope conductance in the linear region of the current-voltage relationship (-40 to 0 mV) for the hair cells located in the different zones. Gp/Gs average values (4.1 +/- 2.1, n = 15) from currents in peripheral hair cells were higher than those from intermediate hair cells (2.3 +/- 0.8, n = 4) and central hair cells(1.9 +/- 0.8, n = 21). The statistically significant differences (P < 0.001) in Gp/Gs ratios could be accounted for by KA channels being preferentially expressed in peripheral hair cells. Hair cell electrophysiological properties in animals pretreated with streptomycin were investigated at approximately 3 wk and approximately 9-10 wk post injection sequence (PIS). At 3 wk PIS, hair cells (all zones combined) had a statistically significantly (P < 0.001) lower Cm (4.6 +/- 1.1 pF, n = 24) and a statistically significantly (P < 0.01) lower Gp(48.4 +/- 20.8 nS, n = 26) than control animals (Cm = 6.2 +/- 1.6 pF, n = 36; Gp = 66 +/- 38.9 nS, n = 40). Regional differences in values of Vz, as well as the distribution of outward and inward rectifying currents, seen in control animals, were still obvious. But, differences in the relative contribution of the expression of the different ionic current components changed. This result could be explained by a relative decrease in IKA compared with IKD during that interval of regeneration, which was particularly evident in peripheral hair cells. (ABSTRACT TRUNCATED)

Animals↗
PubMed1981

Compensation mechanisms for experimental reduction of the functional capacity in the guinea pig placenta. II. Changes in the trophoblast of the labyrinth.

The functional capacity of the placenta of the guinea pig has been reduced in four different ways. It has been investigated whether changes in the trophoblast of the labyrinthine part of the placenta occurred which could be interpreted as a compensation mechanism for the reduction of the capacity. No significant decrease of the thickness of the maternofetal barrier could be measured nor did enlargement by microvilli of the apical and basal surface of the syncytium change significantly. Activities of the enzymes glucose-6-phosphate dehydrogenase, lactate dehydrogenase, glucose-6-phosphatase and adenosine triphosphatase showed a great variation, but no differences in activities could be demonstrated. Further, the number of cytotrophoblastic cells was widely spread and no significant difference could be observed, although sometimes large and apparently newly formed parts of lobulus were observed.

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