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O Candia

Publications and source records attributed to O Candia.

15 recordsLinked to original sources
PubMed1993

Influence of filter supports on transport characteristics of cultured A6 kidney cells.

Amphibian A6 kidney cells grown on Anocell filters developed a transepithelial potential difference of 37 mV, a short-circuit current (Isc) of 8 microA/cm2, and a resistance of 5 k omega.cm2. Other observations suggested a viable arginine vasopressin (AVP) V2 receptor-second messenger pathway in these cells: 1) AVP increased both an amiloride-sensitive Isc and adenosine 3',5'-cyclic monophosphate (cAMP) formation, and 2) scanning electron micrographs of A6 cells cultured on Anocell and ICN Cellagen filters demonstrated increased microvilli formation on the apical surface after AVP action. However, osmotic water flow (JV) across A6 cells on filter supports was not altered by either AVP or the permeable cAMP analogue dibutyryl cAMP (osmotic permeability coefficient = 2.5 x 10(-3) cm/s). Diffusional water flow (Jdw) measured across A6 cells on Anocell filters using tritiated water (THO) ranged from 6 to 8 microliters.min-1.cm-2. Neither AVP nor the membrane-permeabilizing agents amphotericin B and digitonin were able to enhance unidirectional THO fluxes, although amphotericin B increased the Isc. These results suggested that there was an unknown barrier in series with the A6 cells limiting water flow. THO fluxes across filter supports, without an associated cellular monolayer, gave Jdw values in the range 7-30 microliters.min-1.cm-2. Jv across the bare filter support was in the range of 0.3-1.5 microliters.min-1.cm-2, similar to that measured in the presence of an A6 monolayer. These observations suggest that the filter may be rate limiting for transepithelial water flow. Chloride fluxes across Anocell filters showed a stable value of 5 mu eq.h-1.cm-2. These observations exhibit the limitations of filter supports in the study of transport phenomena in cultured cells.

Amiloride↗
PubMed1980

Water permeability of the toad corneal epithelium: the effects of pH and amphotericin B.

The water diffusional permeability of the toad cornea was evaluated from THO measurements, while taking into account the influence of unstirred layers. The corneal epithelium is a restrictive barrier for water diffusion and its permeability can be increased by amphotericin B or Triton X-100. In animals maintained in tap water, the epithelial water permeability was reversibly inhibited by the acidification of the solution bathing the tear side of the cornea. When toads were adapted to a saline environment, a reduction of epithelial water permeability with a loss of sensitivity to changes in the tear side medium pH was observed.

Amphotericin B↗
PubMed1978

Nonhormonal mechanisms for the regulation of transepithelial sodium transport: the roles of surface potential and cell calcium.

An attempt to define the main categories of regulatory mechanisms of transepithelial sodium transport across tight epithelia is presented. In particular, evidence suggesting two types of mechanisms, changes in surface potential and the level of cell Ca, are described in greater detail. We have measured the effects of conditions that affect surface potential on the transepithelial sodium transport. Those conditions that increase the screening of negative charge and therefore depolarize the outer membrane are expected to have effects homologous to a depolarization caused by external current. Indeed, when the composition of the outside solution was modified by (i) increasing ionic strength, (ii) adding polyvalent cations (La+++, Co++, Ni++, Cd++), or (iii) lowering pH, an increase in active Na transport was detected. Moreover, the presence of small concentrations of polyvalent cations which screen surface charge, markedly dampens or even eliminates the effects of pH or ionic strength on Na transport. These findings provide additional support for the notion that a potential-sensitive component regulates Na movements across the apical membrane of the frog skin, and offer a framework to understand the effects of numerous cationic agents on transepithelial transport that hitherto remain unexplained. With respect to the role of intracellular Ca we have found that procedures that increase cell Ca, like removal of sodium in the basal solution or addition of ionophore A23187, reduce transepithelial Na transport. Moreover, conditions that block the increase in cell Ca prevent the inhibition of transport. These observations suggest that the level of intracellular Ca may determine the rate of transepithelial Na transport.

Animals↗
PubMed1977

Urea uptake and translocation in toad urinary bladder: the effect of antidiuretic hormone.

The uptake of C14-urea into everted and noneverted bladder sacs was compared, over short time periods (up to 2 min), with the transepithelial urea fluxes. This method allowed the study of the time course of urea uptake and distribution, while previously this problem was only studied in steady-state conditions. When mucosal uptake was studied no accumulation of C14-urea inside the tissue was observed, indicating that the mucosal border could be the limiting step. Comparative studies of urea and inulin uptake from the serosal side showed that urea equilibrated with the water epithelial cells in less than 30 sec. This accumulation suggested again that the mucosal border is an effective barrier for urea translocation. The kinetics of the increase in urea permeability induced by antidiuretic hormone was also studied and it was similar (T1/2:4.3 min) to the kinetics of the increase in water permeability induced by the hormone (T1/2:5.6 min). A strong parallelism was also observed between the time course of the increases in water and urea permeabilities induced by medium hypertonicity (T1/2 25 and 26 min, respectively). The values obtained for the permeability coefficient ktrans), either at rest or under ADH were similar to those previously reported employing steady-state techniques (28+/-8 and 432+/-25 cm-sec-1-10(-7), respectively).

Animals↗
PubMed1967

Brain stem structures responsible for the electroencephalographic patterns of desynchronized sheep.

Contrary to the results of transecting one half of the rostral pons, unilateral partial lesions of the rostral pons, involving either "specific" or "aspecific" structures, do not prevent the appearance of the desynchronized electroencephalographic patterns of deep sleep in the ipsilateral hemi sphere in cats. This effect, however, is obtained by lesions of the medial as well as lateral tegmental structures of the midbrain. These findings seem to indicate that (i) there is not a single pontine structure or group of structures of crucial importance for the EEG desynchronization of deep sleep; the whole rostral pons appears to contrib ute to the EEG-desynchronizing influ ence; (ii) this influence runs rostrally through the midbrain tegmentum, without following any known fiber pathway.

Animals↗