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Biomedical subjects

C A Berry

Publications and source records attributed to C A Berry.

At least 55 records · Page 3Linked to original sources
PubMed1983

Lack of effect of peritubular protein on passive NaCl transport in the rabbit proximal tubule.

The effect of peritubular protein removal on passive NaCl transport was examined in the isolated rabbit proximal convoluted tubule (PCT). Three modes of passive NaCl transport were tested: (a) paracellular backflux of NaCl, (b) convective flow of NaCl through junctional complexes, and (c) anion gradient-dependent NaCl transport. The effect of peritubular protein removal on the paracellular permeability to NaCl was examined using transepithelial specific resistance. Eight PCT were perfused with ultrafiltrate (UF) and bathed in either serum or UF. Transepithelial specific resistance averaged 14.5 +/- 1.9 in the presence and 13.7 +/- 1.7 omega cm2 in the absence of peritubular protein. The effect of peritubular protein removal on the convective flow of a NaCl solution across functional complexes was examined in the absence of active transport by using colloid osmotic pressure (COP) gradients. 12 PCT were perfused with simple salt solutions in Donnan equilibrium with and without protein at 20 degrees C. A COP gradient of 60.1 and -60.1 mmHg drove only 0.06 and -0.23 nl/min, respectively. These values are approximately 10% of the value predicted for an effect of peritubular protein on NaCl solution flow (1.98 nl/min) and are approximately equal to the value predicted for pure water equilibration for the small osmotic pressure difference between solutions in Donnan equilibrium (0.17-0.18 nl/min). The effect of peritubular protein removal on the passive absorption of NaCl driven by anion concentration gradients was examined in seven PCT perfused with a high chloride solution simulating late proximal tubular fluid and bathed in either serum or UF at 20 degrees C. Volume absorption averaged 0.34 +/- 0.20 in the presence and 0.39 +/- 0.20 nl/mm min in the absence of peritubular protein. In conclusion, peritubular protein removal did not significantly affect any of the three distinct modes of passive NaCl transport tested. The lack of effect of peritubular protein removal on passive paracellular NaCl transport suggests that protein modulates an active transcellular NaCl transport process.

Absorption↗
PubMed1982

Effect of luminal and peritubular HCO3(-) concentrations and PCO2 on HCO3(-) reabsorption in rabbit proximal convoluted tubules perfused in vitro.

The effect of luminal and peritubular HCO3(-) concentrations and PCO2 on HCO3(-) reabsorption was examined in rabbit proximal convoluted tubules perfused in vitro. Increasing luminal HCO3(-) concentration from 25 to 40 mM without changing either peritubular HCO3(-) concentration or PCO2, stimulated HCO3(-) reabsorption by 41%. When luminal HCO3(-) concentration was constant at 40 mM and peritubular HCO3(-) concentration was increased from 25 to 40 mM without changing peritubular PCO2, a 45% reduction in HCO3(-) reabsorption was observed. This inhibitory effect of increasing peritubular HCO3(-) concentration was reversed when peritubular pH was normalized by increasing PCO2. Passive permeability for HCO3(-) was also measured and found to be 1.09 +/- 0.17 X 10(-7) cm2 s-1. Using this value, the passive flux of HCO3(-) could be calculated. Only a small portion (less than 23%) of the observed changes in net HCO3(-) reabsorption can be explained by the passive HCO3(-) flux. We conclude that luminal and peritubular HCO3(-) concentrations after HCO3(-) reabsorption by changing the active H+ secretion rate. Analysis of these data suggest that both luminal and peritubular pH are major determinants of HCO3(-) reabsorption.

Animals↗
PubMed1981

Electrical effects of acidification in the rabbit proximal convoluted tubule.

The electrical characteristics of acidification were examined in isolated rabbit proximal convoluted tubules (PCT). In PCT perfused and bathed with an ultrafiltrate-like solution, the transepithelial potential difference due to active transport (transport PD) averaged -2.4 mV. The transport PD shifted in a negative direction by 1 mV (to -3.4 mV) when carbonic anhydrase inhibitors were added to the bath solution, and in a positive direction by 1.4 mV (to -1.0 mV) when bath sodium bicarbonate concentration was lowered. The positive shift was prevented by addition of either carbonic anhydrase inhibitors or the anion transport inhibitor SITS to the bath. These findings suggested electrogenic acidification. However, when electrogenic sodium transport was inhibited by removal of glucose and alanine from the luminal fluid, a positive PD suggesting electrogenic acidification was not observed. In tubules lacking glucose and alanine in the luminal fluid the rate of total CO2 absorption was 97.2 before and 35.4 pmol.mm-1.min-1 after inhibition of carbonic anhydrase. These findings do not support an independent electronic acidification mechanism. Nonelectrogenic acidification may secondarily after transepithelial PD by changes in transcellular current flow or by changes in paracellular resistance.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
PubMed1981

Influence of peritubular protein on solute absorption in the rabbit proximal tubule. A specific effect on NaCl transport.

The effect of removal of peritubular protein on the reabsorption of various solutes and water was examined in isolated rabbit proximal convoluted tubules (PCT) perfused in vitro. In 22 PCT perfused with ultrafiltrate (UF) and bathed in serum, volume absorption (Jv) was 1.44 nl/mm per min and potential difference (PD) was -3.6 mV. When these same PCT were bathed in a protein-free UF, Jv was reduced 38% without a change in PD. Simultaneous measurements of total CO2 net flux (JTCO2) and glucose efflux (JG) showed that less than 2% of the decrease in JV could be accounted for by a reduction in JTCO2 and JG, suggesting that removal of peritubular protein inhibited sodium chloride transport (JNaCl). Therefore, in eight additional PCT, JNaCl was measured, in addition to PD, Jv, JG, and JTCO2. In these PCT, the decrease in total solute transport induced by removal of bath protein was 201.7 +/- 37.5 posmol/mm per min. JG decreased slightly (9.1 +/- 3.9 posmol/mm per min); NaHCO3 transport did not change (9.2 +/- 6.6 posmol/mm per min); but JNaCl decreased markedly (160.6 +/- 35.7 posmol/mm per min). 80% of the decrease in Jv could be accounted for by a decrease in JNaCl. In 13 additional PCT perfused with simple NaCl solutions, a comparable decrease in Jv and JNaCl was observed when peritubular protein was removed without an increase in TCO2 backleak. In summary, removal of peritubular protein reduced Jv and JNacl, but did not significantly alter PD, JG, JTCO2, or TCO2 backleak. The failure to inhibit JG and JTCO2, known sodium-coupled transport processes, indicates that protein removal does not primarily affect the Na-K ATPase pump system. Furthermore, since PD and TCO2 backleak were not influenced, it is unlikely that protein removal increased the permeability of the paracellular pathway. We conclude that protein removal specifically inhibits active transcellular or passive paracellular NaCl transport.

Animals↗
PubMed1978

Ion selectivity and proximal salt reabsorption.

Electrophysiological techniques were used in isolated perfused superficial (S) and juxtamedullary (JM) rabbit proximal convoluted tubules (PCT) to examine the relative sodium-to-chloride (PNa/PCl) and bicarbonate-to-chloride (PHCO3/PCl) permeability ratios. We found that the great majority of PCT are sodium selective and that PHCO3/PCl depends on the experimental conditions. In the presence of active sodium transport, PHCO3/PCl is high and increases with PNa/PCl. When PHCO3/PCl is determined after inhibition of active sodium transport or at 25 degrees C, PHCO3/PCl approximates the free solution anion mobility ratio of 0.5 and is independent of PNa/PCl. The difference between PHCO3/PCl determined in the presence of and in the absence of active transport suggests that the lowering of bath bicarbonate concentration in the presence of active transport changes both paracellular and transcellular current flow. In addition, we found that during luminal perfusion with high chloride, low bicarbonate, organic solute-free solutions, the transepithelial electrical potential depends on PNa/PCl and PHCO3/PCl. This potential is approximately 4.0 mV in S PCT with low PNa/PCl and falls progressively to zero in JM PCT with high PNa/PCl. From these data we conclude that anion concentration gradients drive an important diffusive flux of sodium chloride through the paracellular pathway only in PCT with low PNa/PCl ratios.

Animals↗
PubMed1978

Relative sodium-to-chloride permeability in the proximal convoluted tubule.

Electrophysiological techniques were used in isolated perfused proximal convoluted tubules (PCT) to examine the effect of changes in bath protein concentration on paracellular properties and of active salt transport on relative sodium-to-chloride permeability (PNa/PCl). Control transepithelial potential difference (PD) and NaCl dilution potentials were determined in tubules perfused and bathed with an ultrafiltrate-like solution. PNa/PCl was calculated from the NaCl dilution potential. In the first series of experiments PD and PNa/PCl were redetermined in the same PCT following three experimental maneuvers known to inhibit active salt transport. Addition of 10(-5) M ouabain to the bath, removal of luminal glucose and alanine, and removal of luminal glucose, alanine, bicarbonate, and acetate reduced PD but did not alter the NaCl dilution potential, and therefore PNa/PCl was constant. Constant PNa/PCl in these experiments suggests a) that lowering bath NaCl concentration does not change transcellular current flow, b) that PNa/PCl reflects the ion selectivity of the paracellular pathway, and c) that the ion selectivity of the paracellular pathway is independent of active salt transport. In the second set of experiments PD and PNA/PCl were redetermined following addition of protein to the bath. Neither PD nor PNa/PCl was altered. Analyses of these data argue against modulation of paracellular permeability by bath protein in the in vitro rabbit PCT and suggest that the ion selectivity of the paracellular pathway is determined predominantly by junctional complexes rather than lateral intercellular spaces.

Animals↗
PubMed1976

Alteration of basal ganglia evoked responses by reserpine and L-dopa.

The effects of reserpine and L-Dopa on basal ganglia evoked potentials were investigated in cats. The caudate response resulting from substantia nigra stimulation and the substantia nigra response elicited by globus pallidus stimulation were increased at several hours after the systemic administration of reserpine. L-Dopa in the presence of dopa decarboxylase inhibition (MK-486) depressed these responses and reversed the effect of reserpine at 0.5 h after administration. Reserpine did not reverse the L-Dopa effect. Reserpine and L-Dopa caused no significant change in responses between other basal ganglia structures. These data give evidence that the basal ganglia are major sites for reserpine and L-Dopa action.

Animals↗
PubMed1976

Medical legacy of Skylab as of May 9, 1974: the manned Skylab missions.

The purpose of these summary remarks is to put into proper focus the magnificent achievement created by the Skylab Medical Team in concert with their engineering colleagues and most importantly, the astronauts who had to serve as both investigators and subjects. Indeed, by their ingenuity and capability of handling the numerous problems encountered due to engineering deficiencies, they have shown man to be indispensable in long-duration space flight.

Adult↗
PubMed1975

Nonelectrolyte permeability of the paracellular pathway in Necturus proximal tubule.

Micropuncture experiments were performed on Necturus proximal tubule using stationary microperfusion and microrecollection techniques. The transepithelial movement of the extracellular marker, sucrose, was used to investigate the passive permeability of the paracellular shunt pathway under steady-state conditions, during spontaneous reabsorption and water flow induced by an external osmotic gradient. Measurements were made of the sucrose permeability (P-s) efflux, net flux, and of net volume flow. True P-s determined in the absence of net volume flow and transepithelial gradient was 0.96 10-6 cm s-1. Both ouabain and isotonic volume expansion decreased shunt P-s. During reabsorption, solute-coupled water flow increased apparent P-s and net sucrose flux equalled efflux. Osmotic water flow from lumen to plasma decreased apparent P-s, with net sucrose flux equal to efflux; whereas osmotic flow from plasma to lumen increased apparent P-s but no net flux was observed. It is concluded that changes in P-s can be interpreted as relative alterations of the tight junction and the lateral spaces and that a portion of the volume flow from lumen to plasma proceeds via the tight junction.

Animals↗