Biomedical subjects

Q R Smith

Publications and source records attributed to Q R Smith.

At least 55 records · Page 3Linked to original sources

PubMed1988

Regulation of brain and cerebrospinal fluid calcium by brain barrier membranes following vitamin D-related chronic hypo- and hypercalcemia in rats.

Male Fischer-344 rats, 21 days old, were fed diets containing 0 (LOD), 2,200 (CONT), or 440,000 (HID) international units of vitamin D3 per kilogram for 12 weeks. [Ca] was measured in plasma, CSF, brain, and choroid plexus. In addition, 45Ca and 36Cl transfer coefficients (KCa and KCl) for uptake from blood into CSF and brain were determined. Although plasma ionized [Ca]s in LOD and HID rats were 50% and 136%, respectively, of values in CONT animals, CSF and brain [Ca]s ranged from only 85% to 110% of respective CONT values. Choroid plexus [Ca] was increased by 37% after HID diet, but was decreased only 10% after LOD. KCa values at CSF, parietal cortex, and pons-medulla were negatively correlated with plasma ionized [Ca], whereas KCl values at CSF and brain were not different between the diet groups. The findings demonstrate that central nervous system [Ca] is maintained during chronic hypo- or hypercalcemia by saturable transport of Ca at brain barrier membranes. This transport does not seem to involve modulation by 1,25-dihydroxyvitamin D3.

Animals↗

PubMed1988

Blood-brain barrier transport of 1-aminocyclohexanecarboxylic acid, a nonmetabolizable amino acid for in vivo studies of brain transport.

Regional transport of 1-aminocyclohexanecarboxylic acid (ACHC), a nonmetabolizable amino acid, across the blood-brain barrier was studied in pentobarbital-anesthetized rats using an in situ brain perfusion technique. The concentration dependence of influx was best described by a model with a saturable and a nonsaturable component. Best-fit values for the kinetic constants of the frontal cortex equaled 9.7 X 10(-4) mumol/s/g for Vmax, 0.054 mumol/ml for Km, and 1.0 X 10(-4) ml/s/g for KD in the absence of competing amino acids. Saturable influx could be reduced by greater than 85% by either L-phenylalanine or 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid, consistent with transport by the cerebrovascular neutral amino acid transport system. The transport Km for ACHC was one-fifth that for the more commonly used homologue, 1-aminocyclopentanecarboxylic acid, and was similar to values for several natural amino acids, such as L-methionine, L-isoleucine, and L-tyrosine. The results indicate that ACHC may be a useful probe for in vivo studies of amino acid transport into brain.

Amino Acids↗

PubMed1988

A compartmental analysis of solute transfer and exchange across blood-nerve barrier.

A three-compartment model was derived to analyze solute exchange among plasma, peripheral nerve epineurium, and endoneurium. The model was fit to measured tibial-nerve epineurial and endoneurial contents of [14C]sucrose after intravenous bolus injection of tracer in pentobarbital sodium-anesthetized rats. The transfer constant (K) for tracer at epineurial vessels approximated 1.1 X 10(-3) ml.s-1.g whole-nerve-1. K at the blood-nerve barrier (BNB) equaled 1.36-1.51 X 10(-5) ml.s-1.g endoneurium-1. The endoneurial uptake data were analyzed also by a simplified two-compartment model incorporating solute exchange between plasma and endoneurium. K at the BNB (1.46 X 10(-5) ml.s-1.g endoneurium-1), determined by multiple uptake time graphic analysis, was only threefold greater than K at the blood-brain barrier. The transfer constant at the perineurium alone was determined in situ and equaled (1 X 10(-6) ml.s-1.g endoneurium-1. Calculated permeability coefficients (X 10(-8) cm/s) equaled 3.2 at the perineurium, 23 at the endoneurial capillaries, and 3.2 at the brain vasculature. The results demonstrate that for hydrophilic nonelectrolytes 1) flux across the perineurium contributes significantly to solute uptake from plasma into the endoneurium; 2) although nerve capillaries are more permeable than brain capillaries, the tissues of the BNB function as a unit to markedly restrict solute diffusion into the endoneurium; and 3) a two-compartment analysis accurately describes hydrophilic solute transfer from plasma into peripheral nerve.

Animals↗

PubMed1987

Facilitated transport of melphalan at the rat blood-brain barrier by the large neutral amino acid carrier system.

Melphalan has been reported to be actively transported into tumor cells by two amino acid carrier systems. As amino acids are transported across cerebral capillaries by a facilitated mechanism, studies were undertaken to assess whether or not melphalan was transported similarly, and additionally to determine melphalan's plasma and brain pharmacokinetics. The brain uptake of [14C]melphalan was measured by an in situ brain perfusion technique in the anesthetized rat utilizing [14C]-melphalan. The cerebrovascular permeability-surface area product of [14C]melphalan was calculated at cold melphalan concentrations from O to 16.3 mumol/ml. The permeability-surface area product was concentration dependent and decreased from 10.8 +/- 0.6 (+/- SE) X 10(-4)S-1 at 0.02 mumol/ml melphalan to 5.4 +/- 0.3 X 10(-4)S-1 at 16.3 mumol/ml. The system became saturated at a concentration in excess of 0.1 mumol/ml. The Michaelis-Menten parameters Vmax and Km, determined by nonlinear regression analysis of the permeability-surface area product data, equaled 0.9 +/- 0.3 X 10(-4) mumol/s/g and 0.15 +/- 0.06 mumol/ml, respectively, for the saturable component of melphalan's brain uptake. The Kd of the nonsaturable component was 5.3 +/- 0.03 X 10(-4)S-1. Addition of the amino acid 1-phenylalanine to the brain perfusate inhibited the saturable component of melphalan's brain uptake. The analysis of the plasma and brain concentrations of melphalan by high-performance liquid chromatography, following i.v. melphalan administration, demonstrated that approximately 15% of the drug that was present in plasma entered the brain. These data suggest that the brain uptake of melphalan is facilitated, demonstrating concentration-dependent uptake, saturation, and inhibition, and that melphalan shares the large neutral amino acid carrier system at the blood-brain barrier.

Amino Acids↗

PubMed1987

Altered blood-nerve barrier permeability to small molecules in experimental diabetes mellitus.

Permeability-surface area products (PA) were determined with a quantitative in vivo injection technique at the blood-nerve barrier of tibial nerve, and at the blood-brain barrier, in control and streptozotocin-induced diabetic rats. The PA product for [14C]mannitol at the blood-nerve barrier was increased by 100% in diabetic animals, 3.12 +/- 0.15 X 10(-5) ml X s-1 X g-1, compared with controls, 1.61 +/- 0.10 X 10(-5) ml X s-1 X g-1. In contrast, PA for [14C]mannitol at the blood-brain barrier was unaltered in the diabetic animals. Following intravenous injection, no leakage of microperoxidase across the perineurium or endoneurial vessels of diabetic rats could be demonstrated by morphological techniques. Nerve blood-space, as determined with intravenous [3H]inulin, and blood-nerve barrier surface area as determined by morphometric methods, did not differ in diabetic when compared to control animals. Thus, the calculated permeability coefficient for [14C]mannitol at the blood-nerve barrier was about 100% greater in diabetic nerve compared to control nerves. The increased permeability was accompanied by a 7% increase in nerve-water content and a 32% decrease in motor-nerve conduction velocity. The results demonstrate a specific vulnerability of nerve as compared to brain in an animal model of diabetes mellitus. Chronically altered permeability to small water-soluble molecules reduces the protective effect of salt impermeability at the blood-nerve barrier against nerve edema, and may be an important pathogenic mechanism in diabetic neuropathy.

Animals↗

PubMed1987

Kinetics of neutral amino acid transport across the blood-brain barrier.

Neutral amino acid (NAA) transport across the blood-brain barrier was examined in pentobarbital-anesthetized rats with an in situ brain perfusion technique. Fourteen of 16 plasma NAAs showed measurable affinity for the cerebrovascular NAA transport system. Values of the transport constants (Vmax, Km, KD) were determined for seven large NAAs from saturation studies, whereas Km values for five small NAAs were estimated from inhibition studies. These data, together with our previous work, provide a complete set of constants for prediction of NAA influx from plasma. Among the NAAs, Vmax varied at least fivefold and Km varied approximately 700 fold. The apparent affinity (1/Km) of each NAA was related linearly (r = 0.910) to the octanol/water partition coefficient, a measure of NAA side-chain hydrophobicity. Predicted influx values from transport constants and average plasma concentrations agree well with values measured using plasma perfusate. These results provide accurate new estimates of the kinetic constants that determine NAA transport across the blood-brain barrier. Furthermore, they suggest that affinity of a L-alpha-amino acid for the transport system is determined primarily by side-chain hydrophobicity.

Amino Acids↗

PubMed1987

Phenylalanine transport across the blood-brain barrier as studied with the in situ brain perfusion technique.

Unidirectional L-phenylalanine transport into six brain regions of pentobarbital-anesthetized rats was studied using the in situ brain perfusion technique. This technique allows both accurate measurements of cerebrovascular amino acid transport and complete control of perfusate amino acid composition. L-Phenylalanine influx into the brain was sodium independent and could be described by a model with a saturable and a nonsaturable component. Best-fit values for the kinetic constants in the parietal cortex equaled 6.9 X 10(-4) mumol/s/g for Vmax, 0.011 mumol/ml for Km, and 1.8 X 10(-4) ml/s/g for KD during perfusion with fluid that did not contain competing amino acids. D-Phenylalanine competitively inhibited L-phenylalanine transport with a Ki approximately 10-fold greater than the Km for L-phenylalanine. There were no significant regional differences in Km, KD, or Ki, whereas Vmax was significantly greater in the cortical lobes than in the other brain regions. L-Phenylalanine influx during plasma perfusion was only 30% of that predicted in the absence of competing amino acids. Competitive inhibition increased the apparent Km during plasma perfusion by approximately 20-fold, to 0.21 mumol/ml. These data provide accurate new estimates of the kinetic constants that describe L-phenylalanine transport across the blood-brain barrier. In addition, they indicate that the cerebrovascular transfer site affinity (1/Km) for L-phenylalanine is three- to 12-fold greater than previously estimated in either awake or anesthetized animals.

Amino Acids↗

PubMed1987

Transfer of nonelectrolytes from blood into peripheral nerve endoneurium.

Permeability-surface area (PA) products were determined for the transfer of seven nonelectrolytes across the blood-nerve barrier (BNB) of rat tibial nerve using a quantitative in vivo injection technique. PA values at the BNB for slowly penetrating nonelectrolytes such as urea, mannitol, L-glucose, and sucrose differed by less than threefold from values at the blood-brain barrier in the same animals. Permeability coefficients for transfer across the BNB were calculated assuming both endoneurial capillaries and perineurium contribute to solute flux into endoneurium. Total BNB surface area was determined as 175 cm2/g with morphometric techniques. Calculated permeability coefficients for slowly penetrating nonelectrolytes ranged from 7 X 10(-8) cm/s for sucrose to 4 X 10(-7) cm/s for urea and were directly proportional to solute lipid solubility as measured by the octanol-water partition coefficient. BNB permeability coefficients for sucrose, mannitol, L-glucose, and urea were within 60% of values at cerebral capillaries, of the same order of magnitude as values at aporous lipid membranes, and 100-1,000 times less than values at most nonneural capillaries, such as in skeletal muscle. These results demonstrate that the BNB markedly restricts the transfer of hydrophilic nonelectrolytes between plasma and endoneurium and that diffusion restriction of the BNB is comparable to that of the blood-brain barrier.

Animals↗

PubMed1986

Calcium influxes into brain and cerebrospinal fluid are linearly related to plasma ionized calcium concentration.

Unidirectional Ca influxes into brain and cerebrospinal fluid (CSF) were measured at different plasma concentrations of ionized Ca ([Ca]i) in pentobarbital-anesthetized rats. Plasma [Ca]i was varied acutely from 0.6 to 3.0 mumol/ml by intravenous infusion of EGTA, NaCl or CaCl2 or by thyroparathyroidectomy. Ca influx was determined from the 15-min uptake of 45Ca after intravenous injection. There were significant regional differences in 45Ca uptake into the CNS, with a approximately 20-fold greater rate into ventricular CSF than into frontal cortex. Autoradiographs of 45Ca uptake demonstrated that uptake into frontal cortex reflects primarily transport across the cerebral capillaries, whereas uptake into ventricular CSF reflects transport across the choroid plexuses. At both sites, Ca influx was a linear function of plasma [Ca]i and extrapolated to zero at [Ca]i = 0. Infusion of EGTA or CaCl2 did not alter the integrity of the blood-brain barrier, as determined by the permeability to [14C]sucrose. These results indicate that Ca influx into the CNS is not regulated by a saturable mechanism that is sensitive to acute changes in plasma [Ca]i. The proportionality between influx and concentration is suggestive of passive diffusional transport. The brain is protected from acute changes in plasma [Ca]i by the low cerebrovascular permeability to Ca, approximately 5 X 10(-8) cm/s.

Animals↗

PubMed1986

Cerebrovascular permeability coefficients to sodium, potassium, and chloride.

CSF and regional brain concentrations of 42K, 22Na, 36Cl, and [14C]mannitol were determined 3-45 min after intravenous injection of the tracers in pentobarbital-anesthetized rats. Rapid influx of 36Cl and 22Na into ventricular CSF immediately established concentration gradients from CSF to brain extracellular fluid. The CSF contribution to brain uptake of tracers was greatest in periventricular brain regions, where brain 36Cl concentrations were up to ninefold higher than concentrations in regions distant from ventricular CSF. Acetazolamide (20 mg kg-1 i.p.), an inhibitor of CSF formation, decreased 36Cl uptake into CSF and into periventricular brain regions but not into frontal cortex. 36Cl uptake into brain was unidirectional for 10 min after intravenous injection, and, during that period, diffusion from ventricular CSF did not contribute to uptake in the frontal cortex. Therefore, cerebrovascular permeability coefficients could be calculated from tracer concentrations in frontal cortex at 10 min and equaled, in cm s-1, 13.5 X 10(-7) for 42K, 1.4 X 10(-7) for 22Na, 0.9 X 10(-7) for 36Cl, and 1.5 X 10(-7) for [14C]mannitol. The low cerebrovascular permeabilities to K, Na, and Cl, comparable to those of some cell membranes, and the permselectivity (K much greater than Na greater than Cl) suggest that a significant fraction of ion transport across cerebral capillaries is transcellular, i.e., across the endothelial cell membrane.

Acetazolamide↗

PubMed1986

Homeostasis of brain and cerebrospinal fluid calcium concentrations during chronic hypo- and hypercalcemia.

Three-week-old rats were made hypocalcemic or hypercalcemic by being fed diets low or high in Ca. Both total and ionized [Ca]s in the plasma decreased about 40% and remained depressed for 4 weeks in rats fed a low-Ca diet. Plasma [Ca]s in rats fed a high-Ca diet increased by 30% and remained elevated for 7 weeks. After 8 weeks on the diets, cerebrospinal fluid (CSF) [Ca] changed by less than 30% whereas brain [Ca] changed by less than 20% of the chronic changes in plasma ionized [Ca]. Assuming a brain extracellular volume of 20% and noting that brain extracellular volume equilibrates freely with CSF, the findings demonstrate only small perturbations in the Ca content of the brain cellular compartment during sustained hypo or hypercalcemia. Partial regulation of CSF and brain extracellular Ca suggests a role for the blood-brain barrier in regulating CNS [Ca] during chronic changes in plasma [Ca].

Animals↗

PubMed1986

Kinetics of amino acid transport at the blood-brain barrier studied using an in situ brain perfusion technique.

The in situ brain perfusion technique of Takasato et al. allows accurate measurements of regional amino-acid influx across the blood-brain barrier. Influx can be determined in the absence of competing amino acids, using saline perfusate, or in the presence of physiological concentrations of amino acids, using plasma or blood perfusate. The concentration dependence of cerebrovascular LNAA transport is best described by a model with a Michaelis-Menten saturable and a nonsaturable component. Vmax values for four LNAAs are similar and average 10 X 10(-4) mumol X sec-1 X g-1. In contrast, Km values differ by up to 10-fold with the lowest value for leucine. Competitive inhibition increases the apparent Km for transport from plasma by approximately 20-fold. These data provide accurate new estimates of the kinetic constants that describe amino-acid transport across the blood-brain barrier. In addition, they indicate that the cerebrovascular transport capacity (Vmax) and affinity (1/Km) are greater than previously reported with the brain uptake index technique.

Amino Acids↗

PubMed1985

Regional cerebrovascular transport of leucine as measured by the in situ brain perfusion technique.

Leucine influx into six brain regions was determined in anesthetized rats with the in situ brain perfusion technique using either saline or plasma perfusate. This technique has several advantages over other methods such as the brain uptake index (BUI) technique. The concentration dependence of L-leucine influx was best described by a model with a saturable and a nonsaturable component. For the saturable component, Vmax equaled 10.67 +/- 0.21 X 10(-4) mumol s-1 g-1 and Km equaled 0.0257 +/- 0.0009 mumol ml-1, whereas the constant of nonsaturable diffusion (Kd) equaled 0.957 +/- 0.067 X 10(-4) s-1 in the parietal lobe during saline perfusion. Vmax was higher in the cortical lobes than in other brain areas, probably owing to a greater capillary surface area. There were no regional differences in Km or Kd. The apparent Km for L-leucine during plasma perfusion was 20 times greater than the Km during saline perfusion, and 3 to 4 times greater than the plasma leucine concentration, owing to competitive inhibition of leucine transport by other large neutral amino acids in plasma. These results for Vmax, Km, and Kd differ by three- to fourfold from previous estimates obtained with the BUI technique. The high apparent Km during plasma perfusion indicates that leucine influx is a linear function of plasma concentration up to 0.5 mumol ml-1 when the plasma concentrations of other amino acids remain constant, whereas influx would be approximately constant when plasma concentrations of all large neutral amino acids increased or decreased by a constant fraction.

Amino Acids↗

PubMed1985

Facilitated transport of glucose from blood into peripheral nerve.

D-Glucose is the major substrate for energy metabolism in peripheral nerve. The mechanism of transfer of glucose across the blood-nerve barrier is unclarified. In this study an in situ perfusion technique was utilized, in anesthetized rats, to examine monosaccharide transport from blood into peripheral nerve. Unidirectional influxes of D-[14C]glucose, L-[14C]glucose, and [14C]3-O-methyl-D-glucose across capillaries of the tibial nerve were measured at different perfusate concentrations of unlabelled D-glucose. The permeability-surface area product (PA) for D-[14C]glucose and [14C]3-O-methyl-D-glucose decreased, whereas the PA for L-[14C]glucose remained constant, as the perfusate concentration of D-glucose was increased. In the presence of no added unlabelled D-glucose in the perfusate, the PA for L-[14C]glucose equaled one-fifth the PA for D-[14C]glucose. These results demonstrate self-saturation, competitive inhibition, and stereospecificity of glucose transfer, and for the first time show a unidirectional facilitated transport mechanism for D-monosaccharides at capillaries of mammalian peripheral nerve. The data were fit to a model for facilitated transport and passive diffusion. The half-saturation constant and maximal rate of transport for the saturable component of D-glucose influx equaled 23 +/- 11 mumol X ml-1 and 6.6 +/- 3.2 X 10(-3) mumol X s-1 X g-1, respectively. The constant of nonsaturable glucose influx equaled 0.5 +/- 0.1 X 10(-4) s-1. At normal plasma glucose concentrations, the saturable component comprises about 80% of total D-glucose influx into nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

Kinetic analysis of cerebrovascular isoleucine transport from saline and plasma.

The concentration dependence of regional isoleucine transport across the blood-brain barrier was determined in anesthetized rats with the in situ brain perfusion technique of Takasato et al. [Am. J. Physiol. 247, H484-493 (1984)]. This technique allows, for the first time, accurate measurements of cerebrovascular amino acid transport in the absence of competing amino acids using saline perfusate, and in the presence of physiological concentrations of amino acids using plasma perfusate. Cerebrovascular isoleucine transport from saline perfusate followed Michaelis-Menten saturation kinetics where Vmax = 9 - 11 X 10(-4) mumol X s-1 X g-1 and Km = 0.054-0.068 mumol X ml-1 in six brain regions. A component of nonsaturable transport was not detected in any brain region even though perfusate isoleucine concentration was increased to greater than or equal to 150 times the normal plasma concentration. Isoleucine influx during plasma perfusion was only 8% of that predicted from the saline perfusion data due to transport inhibition by competing amino acids in plasma. Competitive inhibition increased the apparent Km for isoleucine transport from plasma by greater than or equal to 24-fold to 1.5-1.7 mumol X ml-1. These data provide accurate new estimates of the kinetic constants that describe amino acid transport across the blood-brain barrier. In addition, they indicate that the cerebrovascular transfer-site affinity (1/Km) for isoleucine is approximately fivefold greater than previously reported with the brain uptake index technique.

Animals↗

PubMed1985

Sciatic nerve blood flow measured by laser Doppler flowmetry and [14C]iodoantipyrine.

Blood flow was examined in sciatic nerves of pentobarbital-anesthetized rats by means of laser Doppler flowmetry (LDF) and intravenous [14C]iodoantipyrine infusion. Continuous LDF signals demonstrated slow oscillations and acute, pressure-related changes in flow. The steady-state LDF signal was related linearly to nerve blood flow, as measured with [14C]iodoantipyrine, in intact nerves and nerves stripped of the epineurium. In 14 intact nerves, nerve blood flow averaged 0.27 +/- 0.03 (SE) ml X min-1 X g-1, whereas it averaged 0.13 +/- 0.01 in 5 stripped nerves. Autoradiographs of [3H]-nicotine-infused nerves and intra-arterial injection of 57Co-labeled microspheres demonstrated that flow was not uniform throughout the nerve cross section. The results indicate that LDF can be used to examine nerve blood flow in vivo, demonstrate a linear relation between the LDF signal and flow, and establish absolute values for blood flow in intact and stripped nerves of the anesthetized rat.

Animals↗

PubMed1985

Active transport of chloride by lateral ventricle choroid plexus of the rat.

The nature of Cl transport and its relation to Na and K transport were analyzed in adult rat lateral ventricle choroid plexus incubated in cerebrospinal fluid (CSF) medium at 37 degrees C and PCO2 = 30 mmHg. In synthetic CSF (extracellular Cl [( Cl]o) = 130 mM), the intracellular Cl [( Cl]i) was three times that estimated for passive distribution. Choroid plexus [Cl]i was not determined by Donnan distribution because [Cl]i remained constant at approximately 50 mM while the [K]i/[K]o ratio was varied 10-fold by drugs and cation substitutions. A [Cl]i/[Cl]o ratio of approximately 0.38 was found when [Cl]o was varied from 15 to 130 mM by isosmotic replacement of Cl with methyl sulfate or isethionate. However, the [Cl]i/[Cl]o ratio increased to greater than 1.0 when [Cl]o was lowered below 5 mM. Reduction in bath temperature to 15 degrees C (CSF PCO2 = 50 mmHg) increased both [Cl]i/[Cl]o and [HCO3]i/[HCO3]o to approximately 0.6. SITS, an inhibitor of Cl-HCO3 transport, reduced [Cl]i by 18 mM, decreasing the [Cl]i/[Cl]o ratio close to the equilibrium value. In contrast, neither furosemide (10(-3) M) nor low CSF [Na]o (3 mM) reduced Cl accumulation. It is concluded that uphill movement of Cl into choroid plexus epithelium occurs primarily by Cl-HCO3 antiport and not by Na-Cl symport.

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

PubMed1985

Cl-HCO3 exchange in choroid plexus: analysis by the DMO method for cell pH.

[14C]DMO distribution was used to measure steady-state intracellular pH (pHi) and [HCO3]i in adult rat choroid plexus (CP) incubated in synthetic cerebrospinal fluid (CSF) for 30 min. In controls at 37 degrees C, mean pHi (6.95 at PCO2 = 30 mmHg) was close to corresponding in vivo values; and [HCO3]i/[HCO3]csf, i.e., rHCO3, was 0.37. At normal [HCO3]csf = 18 mM, cell HCO3 was accumulated threefold above electrochemical equilibrium (as estimated from Em = -50 mV). [HCO3]i decreased proportionally with [HCO3]csf, as the latter was altered from 47 to 9 mM; in severe extracellular acidosis [( HCO3]csf = 3.7 mM), [HCO3]i was not reduced further and so rHCO3 rose to 0.66. Except in low [HCO3]csf, acetazolamide and ouabain (10(-4) M) caused small depletion of cell HCO3. 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid lowered [HCO3]i by 60%, thus decreasing rHCO3 (0.16) and rCl (0.25) to values close to estimated equilibrium distribution (0.15). Substitution of CSF Cl with isethionate resulted in marked alkalinization of pHi when [Cl]csf was depleted to 12 mM. Augmented PCO2 associated with temperature reduction to 15 degrees C elevated [HCO3]i, thereby increasing rHCO3 (to 0.66) as well as rCl. Anion distribution ratios indicate heteroanion exchange in mammalian CP.

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