Biomedical subjects

A Aperia

Publications and source records attributed to A Aperia.

At least 91 records · Page 5Linked to original sources

PubMed1993

Growth regulation of LLC-PK1 cells: lack of effect of Na(+)-loading.

To gain more information about the growth regulation of renal epithelial cells, we examined the growth stimulatory effect of serum and intracellular sodium in the renal epithelial cell line, LLC-PK1. In subconfluent LLC-PK1 cells serum-starved for 5 days and exposed to [3H]thymidine for 24 h, 22.9% of the cells synthesized DNA. Stimulation with 10% foetal calf serum (FCS) caused an almost three-fold increase in the fraction of labelled nuclei (62.2%). Serum-starved LLC-PK1 cells exposed to 10% FCS responded with an increased abundance of c-jun transcripts. The maximal expression of the c-jun transcripts occurred at 60 min and declined 120 min after serum stimulation. It has been suggested that an increase in Na+ influx plays a role in the growth regulation of renal epithelial cells. This prompted us to study the effect of intracellular Na+ loading on the growth response of LLC-PK1 cells. Serum-starved LLC-PK1 cells were incubated in a low K+ medium or exposed to Nystatin. Incubation in a low K+ medium or with Nystatin resulted in a marked increase in intracellular Na after only 5 min. A low K+ medium did not significantly influence the intracellular pH. No effect was observed on DNA synthesis or the abundance of c-jun transcripts in LLC-PK1 cells. Nor did Na+ loading enhance the growth stimulatory effect of serum. The results suggest that an increase in intracellular sodium does not directly regulate the growth of renal epithelial cells.

Animals↗

PubMed1993

Renal Na+,K(+)-ATPase in Dahl salt-sensitive rats: K+ dependence, effect of cell environment and protein kinases.

Na+,K(+)-ATPase in renal epithelial cells plays an important role in the regulation of Na+ balance, extracellular volume and blood pressure. The function of renal Na+,K(+)-ATPase in Dahl salt-sensitive (DS) rats, an animal model for salt-sensitive hypertension, and Dahl salt-resistant (DR) rats has been studied. In Na+,K(+)-ATPase partially purified from renal cortex, affinities and the Hill coefficients for Na+ and K+ activation were similar in DS and DR rats. Only one component of low ouabain affinity site was found in both strains, indicating the presence of the alpha 1 isoform. Protein kinase C and cAMP-dependent protein kinase phosphorylated Na+,K(+)-ATPase alpha subunit in DS and DR rats, and the phosphorylation by protein kinase C was associated with an inhibition of enzyme activity. The kinetic parameters for K+ activation were also studied in a preparation of basolateral membranes and were found to be similar in DS and DR rats. In a preparation of cortical tubule cells, Na+,K(+)-ATPase activity was determined as ouabain-sensitive oxygen consumption (OS QO2). Maximal OS QO2, measured in Na+ loaded cells, was the same in DS and DR rats. The K0.5 for K+ was significantly lower in DS than DR rats (0.163 +/- 0.042 vs. 0.447 +/- 0.061 mM, P < 0.05), indicating that factors regulating Na+,K(+)-ATPase activity in intact cells are altered in DS rats. Kinetic parameters for Na+ activation in cells were the same in both strains. In summary, the function of renal Na+,K(+)-ATPase molecule is not altered in DS rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

High-salt diet upregulates activity and mRNA of renal Na(+)-K(+)-ATPase in Dahl salt-sensitive rats.

We examined the effect of a high-salt (HS) diet on the regulation of renal cortical Na(+)-K(+)-adenosinetriphosphatase (Na(+)-K(+)-ATPase) in young Dahl salt-sensitive (DS) and salt-resistant (DR) rats. The activity of Na(+)-K(+)-ATPase, determined in permeabilized proximal tubule segments, was similar in DS and DR rats on normal salt (NS) diet. HS diet resulted in a twofold increase in proximal tubule Na(+)-K(+)-ATPase activity in DS rats but not in DR rats. The mRNA abundance, which was also similar in DS and DR rats on NS diet, increased after 2 days on HS diet in both innervated and denervated kidneys from DS rats but had no effect in DR rats. The activity of Na(+)-K(+)-ATPase and the content of alpha 1- and beta-protein in cortical homogenate were similar in DS and DR rats on both NS and HS diets. Treatment with benserazide, an inhibitor of dopa decarboxylase, upregulated proximal tubule Na(+)-K(+)-ATPase activity and increased Na(+)-K(+)-ATPase mRNA in DR rats on HS diet. Taken together, these data indicate that there is a primary defect in the dynamic hormonal regulation of Na(+)-K(+)-ATPase activity in intact tubular cells, which might stimulate Na(+)-K(+)-ATPase transcription.

Animals↗

PubMed1993

Dopamine regulation of renal Na+,K(+)-ATPase activity is lacking in Dahl salt-sensitive rats.

Dopamine is a natriuretic hormone that acts by inhibiting tubular Na+, K(+)-ATPase activity by activation of the dopamine-1 receptor (the thick ascending limb [TAL] of Henle) or by a synergistic effect of dopamine-1 and dopamine-2 receptors (the proximal tubule). The dopamine-1 receptor is coupled to adenylate cyclase. In this article we show that prehypertensive Dahl salt-sensitive (DS) rats have a blunted natriuretic response to dopamine determined during euvolemic conditions compared with Dahl salt-resistant (DR) rats. Furthermore, we have examined the renal tubular effects of dopamine in DS and DR rats. Basal Na+,K(+)-ATPase activity was similar in DS and DR rats. In proximal tubule, dopamine (10(-5) M) inhibited Na+,K(+)-ATPase activity in DR but not in DS rats. The dopamine-2 agonist LY171555 (10(-5) M) together with dibutyryl cyclic AMP (10(-6) M) inhibited proximal tubule Na+,K(+)-ATPase activity in both DS and DR rats. LY171555 alone had no effect. In TAL, the dopamine-1 agonist fenoldopam (10(-5) M) inhibited Na+,K(+)-ATPase activity in DR but not in DS rats. Dibutyryl cyclic AMP (10(-5) M) inhibited TAL Na+,K(+)-ATPase activity in both DS and DR rats. In cell suspensions from the cortex and the medulla, activation of the dopamine-1 receptor significantly increased cyclic AMP content in DR but not in DS rats. The results indicate that DS rats lack the capacity to inhibit tubular Na+,K(+)-ATPase activity because of a defective dopamine-1 receptor adenylate cyclase coupling. This defect may contribute to the impaired natriuretic capacity in DS rats.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1993

Sensitive periods for glucocorticoids' regulation of Na+,K(+)-ATPase mRNA in the developing lung and kidney.

We have previously reported that in the infant rat renal cortex, a saturating dose of glucocorticoid hormones (GC) rapidly increases the abundance of Na+,K(+)-ATPase mRNA. We now show that this effect is dose dependent. In the renal cortex of 10-d-old rats, an increase in renal Na+,K(+)-ATPase mRNA occurs with 2.5 micrograms betamethasone/100 g body weight. In subsequent experiments, performed 6 h after a saturating dose (60 micrograms/100 g body weight), we show that the effect is age dependent. The most marked effects on renal cortical alpha-mRNA were found at 10 d of age (5.3- +/- 0.9-fold). A significant increase was also found in 20-d-old rats (1.6- +/- 0.2-fold), but no effect was found in fetal and 5-d-old rats. Studies were also performed on the lung, where the most marked effect was noted in the perinatal period (2.0- +/- 0.1-fold 2 d before birth and 1.76 +/- 0.2 at 5 d of age), but no effect on alpha-mRNA was found at 10 and 20 d. In one protocol, the effect of betamethasone on renal Na+K(+)-ATPase mRNAs abundance was determined in adult adrenalectomized rats. In these rats, betamethasone induced a significant 1.6- +/- 0.2-fold and 1.8- +/- 0.3-fold increase in renal Na+,K(+)-ATPase mRNA. This effect, however, was significantly smaller than the increase induced in intact 10-d-old rats. GC induction of Na+,K(+)-ATPase mRNA is age and tissue dependent and is dependent on factors other than GC-receptor availability. The GC-sensitive period appears to coincide with the physiologic need for organ maturation.

Age Factors↗

PubMed1993

The effect of dopamine on adenylate cyclase and Na+,K(+)-ATPase activity in the developing rat renal cortical and medullary tubule cells.

Dopamine has an age-dependent natriuretic and diuretic effect. We have investigated the ontogeny of the dopamine response on adenylate cyclase activity and Na+,K(+)-ATPase activity in two different cell populations in the infant (10-d-old) and the adult (40-d-old) rat kidney. Basal- and forskolin-stimulated adenylate cyclase activity in tubular suspensions of renal cortex was 5.4-fold (p < 0.05) higher in the 10-d-old rats than in the 40-d-old rats but unchanged between the ages in a suspension of medullary tubules. The dopamine-1-specific agonist fenoldopam did not stimulate adenylate cyclase activity in the cortical cells from 10-d-old rats but did stimulate activity 51 +/- 16% (p < 0.05) in the 40-d-old rats. In the medullary suspension, fenoldopam stimulated adenylate cyclase activity by 43.5 +/- 5% (p < 0.001) in the 10-d-old rats and by 32.0 +/- 7% (p < 0.01) in the 40-d-old rats. In the isolated proximal convoluted tubule, dopamine inhibited Na+,K(+)-ATPase activity in both the 10-d-old (34 +/- 3%, p < 0.001) and 40-d-old rats (44 +/- 7%, p < 0.001). In contrast, in the medullary thick ascending limb of Henle, inhibition of Na+,K(+)-ATPase activity by fenoldopam was more pronounced in the 10-d-old (56 +/- 6%, p < 0.001) than in the 40-d-old rat (33 +/- 6%, p < 0.001). In summary, the renal tubular effects of dopamine on adenylate cyclase and Na+,K(+)-ATPase activity change during postnatal development in a cell-specific manner.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

PubMed1993

Molecular mechanisms involved in catecholamine regulation of sodium transport.

The catecholamines dopamine and norepinephrine, play a central role in the regulation of sodium homeostasis and blood pressure. Dopamine inhibits tubular Na+, K(+)-ATPase activity and increases sodium excretion. Norepinephrine stimulates Na+, K(+)-ATPase activity and decreases urinary sodium excretion. The signaling pathway by which these two opposite first messengers regulate Na+, K(+)-ATPase activity involves the dopamine-specific protein phosphatase-1 inhibitor, DARPP-32, and the norepinephrine-activated protein phosphatase-2B, calcineurin. Aberrations in the renal dopamine/norepinephrine system may be the cause of alterations in the regulation of sodium excretion during ontogeny and in salt-sensitive hypertension.

Animals↗

PubMed1992

Calcineurin mediates alpha-adrenergic stimulation of Na+,K(+)-ATPase activity in renal tubule cells.

The alpha-adrenergic agonist oxymetazoline increased Na+,K(+)-ATPase activity of single proximal convoluted tubules dissected from rat kidney. Activation of the enzyme by oxymetazoline was prevented by either the alpha 1-adrenergic antagonist prazosin or the alpha 2-adrenergic antagonist yohimbine and was mimicked by the calcium ionophore A23187. The effect of oxymetazoline on Na+,K(+)-ATPase activity was prevented by a specific peptide inhibitor of calcineurin, as well as by FK 506, an immunosuppressant agent known to inhibit calcineurin; these results indicate that the action of oxymetazoline is mediated via activation of calcineurin (a calcium/calmodulin-dependent protein phosphatase). Activation of the Na+,K(+)-ATPase by either oxymetazoline or A23187 was associated with a greater than 2-fold increase in its affinity for Na+. The results provide a biochemical mechanism by which norepinephrine, released from renal nerve terminals, stimulates Na+ retention.

Animals↗

PubMed1992

Sorbinil does not prevent hyperfiltration, elevated ultrafiltration pressure and albuminuria in streptozotocin-diabetic rats.

The effects of aldose reductase inhibition on kidney function were studied in rats with streptozotocin-induced diabetes mellitus. Diabetic rats were fed sorbinil (20 and 50 mg/kg) by daily gastric gavage and were compared with untreated diabetic rats and normal rats. The rats were under daily supervision with regard to blood glucose control, insulin administration and body weight. The aim was to promote continuous body growth and to maintain the blood glucose concentration at around 22 mmol/l without large day-to-day fluctuations. The renal functional changes observed in this well-established diabetic model closely resembled those reported in human Type 1 (insulin-dependent) diabetes mellitus. Sorbinil treatment completely prevented renal cortical sorbital accumulation, but did not abolish kidney enlargement or the increase in ultrafiltration pressure and glomerular filtration rate. Albumin excretion was increased to the same extent in the sorbinil-treated and in the untreated diabetic rats. We conclude that increased metabolism of glucose to sorbitol does not cause the hyperfiltration in rats with streptozotocin-induced diabetes.

Albuminuria↗

PubMed1992

Renal function in very low birth weight infants: normal maturity reached during early childhood.

Development of glomerular and tubular renal function is delayed in preterm infants. To study the pattern of maturation during infancy and childhood, we re-evaluated renal function in 22 very low birth weight infants--in 14 of the infants at 18 months postconceptional age (9 months corrected age) and in the remaining 8 infants at 8 years of age. The glomerular filtration rate remained lower at 9 months corrected age than in term infants of the same postconceptional age: 82 +/- 23 versus 125 +/- 18 ml/min per 1.73 m2 (p < 0.001). At 8 years of age the glomerular filtration rate did not differ from that of healthy control subjects. Effective renal plasma flow, filtration fraction, albumin excretion, maximal concentrating ability, and kidney size determined by ultrasonography were all normal at 8 years of age. We conclude that renal function, which is markedly reduced during the neonatal period in very low birth weight infants, reaches normal maturity by 8 years of age but not by 9 months corrected age.

Albuminuria↗

PubMed1992

Ontogeny of aromatic L-amino acid decarboxylase-containing tubule cells in rat kidney.

Dopamine plays an important role in regulation of renal sodium transport. Proximal tubule cells produce dopamine after decarboxylation of L-DOPA via the enzyme aromatic L-amino acid decarboxylase (AADC). The presence and cellular localization of AADC-like immunoreactivity (-LI) and AADC mRNA were examined during pre- and postnatal development in rat kidney by indirect immunofluorescence and in situ hybridization histochemistry. Few scattered condensations of AADC-immunoreactive (-IR) tubule cells forming a lumen were detected on gestational day 18. From gestational day 21, many AADC-IR tubule cells were observed in the inner cortex, whereas the outer cortex lacked AADC-LI. Within 24 hours of birth, AADC-IR cells in the inner cortex could be identified as proximal tubule cells. During day 3 and 5 there was an increase in number of AADC-IR proximal tubule cells in the inner cortex, leaving less amount of AADC-negative cells in the outer cortex. Starting from day 8, AADC-IR cells could be seen in the outer cortex. An apparent decrease in AADC-immunofluorescence intensity was observed at 40 days, and at 80 days virtually no AADC-LI could be demonstrated. Intrarenal levels of dopamine showed a tendency to increase between 3 and 20 days, and showed significant decreases between 20 to 40 days and between 40 to 80 days. AADC mRNA was not detected in the kidney at 18 hours after birth, but could be observed in the inner cortex at 6 days. At 12, 19 and 40 days AADC mRNA was seen in the entire cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1992

Control of electrolyte transport in the kidney through a dopamine- and cAMP-regulated phosphoprotein, DARPP-32.

1. DARPP-32 is a phosphoprotein regulated by dopamine and cAMP. In its phosphorylated form it acts as an inhibitor of protein phosphatase-1, thereby regulating the phosphorylation state of phosphoproteins in the basal ganglia. 2. In the kidney, DARPP-32 has been detected in the medullary thick ascending limb of Henle (mTAL) and, to a lesser degree, in the proximal convoluted tubule by means of immunohistochemistry and in situ hybridization. 3. In single microdissected tubules of rat kidney, Na+, K(+)-ATPase activity, measured as ouabain-sensitive ATP hydrolysis, has been shown to be inhibited to the same degree by the DA1 agonist fenoldopam, cAMP and a synthesized and phosphorylated DARPP-32 peptide, D32(8-38). 4. It is concluded that the DA1 receptor-mediated inhibition of Na+ transport in the mTAL by dopamine occurs via cAMP accumulation and the phosphoprotein, DARPP-32.

Animals↗

PubMed1992

Sodium-dependent regulation of sodium, potassium-adenosine-tri-phosphatase (Na+, K(+)-ATPase) activity in medullary thick ascending limb of Henle segments. Effect of cyclic-adenosine-monophosphate guanosine-nucleotide-binding-protein activity and arginine vasopressin.

This study examine the regulation Na+, K(+)-ATPase activity in the medullary thick ascending limb of Henle Na+, K(+)-ATPase activity was determined in medullary thick ascending limb of Henle (mtal) segments dissected from rat kidneys. The sodium concentration in the medium (Nam) was 20 or 70 mM. Since the segments were permeabilized, intracellular Na+ (Nai) was assumed to be the same as Nam. Dibuturyl cyclic adenosine monophosphate (dbcAMP) and forskolin inhibited Na+, K(+)-ATPase activity independently of Nam. Arginine vasopressin (AVP) receptors coupled to adenylate cyclase have been identified in the medullary thick ascending limb of Henle. At Nam = 20 mMAVP caused a dose-dependent inhibition of Na+, K(+)-ATPase activity with a maximal effect (49%) at 10(-8) M. This inhibition was abolished in the presence of the adenylate cyclase inhibitor 2,5-dideoxyadenosine (2, 5-DDA). AVP had no effect on Na+, K(+)-ATPase activity in the mTAL at Nam = 70 mM. The guanosine-diphosphate analogue GDP beta S inhibited Na+, K(+)-ATPase activity at Nam = 70 mM but not at Nam = 20 mM. We conclude that increased cyclic adenosine monophosphate (cAMP) levels inhibit Na+, K(+)-ATPase activity in mTAL. AVP can, depending on Nai, produce this effect by adenylate cyclase activation. The guanonine nucleotide binding protein G-protein might be the site of Na(+)-dependence.

Adenosine Triphosphate↗

PubMed1992

High salt diet down-regulates proximal tubule Na+, K(+)-ATPase activity in Dahl salt-resistant but not in Dahl salt-sensitive rats: evidence of defective dopamine regulation.

We examined the regulation of Na+,K(+)-ATPase activity in proximal tubule segments during a high salt diet in prehypertensive Dahl salt-sensitive and salt-resistant rats. Rats were placed on normal salt or high salt diets (0.9% saline as drinking water). During the normal salt diet, Na+,K(+)-ATPase activity was not different between Dahl salt-sensitive and salt-resistant rats. After 2 days and 10 days on a high salt diet, Na+,K(+)-ATPase activity in Dahl salt-resistant rats significantly decreased when compared to Dahl salt-resistant rats on a normal salt diet (P less than 0.01). The decreased Na+,K(+)-ATPase activity in Dahl salt-resistant rats during a high salt diet was reversed by treatment with an inhibitor of aromatic L-amino acid decarboxylase (dopamine synthesizing enzyme), benserazide. In contrast, Na+,K(+)-ATPase activity did not decrease during the high salt diet and benserazide had no effect on Na+,K(+)-ATPase activity in Dahl salt-sensitive rats. These results indicate that Dahl salt-sensitive rats do not have the capacity to down-regulate the proximal tubule Na+,K(+)-ATPase activity during a high salt diet. Indirect evidence suggests that the regulation of Na+,K(+)-ATPase activity by locally produced dopamine is absent in Dahl salt-sensitive rats.

Animals↗

PubMed1992

Calcium supplementation and thyroid hormone protect against gentamicin-induced inhibition of proximal tubular Na+,K(+)-ATPase activity and other renal functional changes.

Gentamicin can cause proximal tubule necrosis. We have shown that inhibition of PT Na+,K(+)-ATPase activity is rapidly induced by gentamicin. We have now investigated whether manipulations known to attenuate the negative effects of gentamicin on renal excretory capacity, i.e. high calcium intake and L-thyroxine treatment, will also attenuate gentamicin-induced inhibition of Na+,K(+)-ATPase activity and ameliorated signs of proximal tubule damage. Rats were gentamicin- or vehicle-treated for 7 days. Sub-groups were given 4% calcium (Ca) supplements or L-thyroxine 20 micrograms 100 g-1 body weight daily. Gentamicin significantly reduced the glomerular filtration rate and increased the urinary excretion of the proximal tubule lysosomal enzyme, N-acetyl-beta-D-glucosaminidase. Gentamicin significantly reduced proximal tubule Na+,K(+)-ATPase activity, measured in single permeabilized proximal tubule segments. Sodium excretion was inversely correlated to proximal tubule Na+,K(+)-ATPase activity. Both calcium and L-thyroxine alleviated all gentamicin-induced side-effects on renal function as well as on proximal tubule Na+,K(+)-ATPase activity. Calcium and L-thyroxine had no significant effect on renal function. L-thyroxine, but not calcium, increased proximal tubule Na+,K(+)-ATPase activity in control rats. Renal cortical tissue gentamicin concentration was not influenced by calcium but was significantly lowered by L-thyroxine. Two procedures which, via different mechanisms, afford protection from gentamicin-induced changes in renal function also give protection from gentamicin-induced inhibition of Na+,K(+)-ATPase activity. This suggests that loss of integrity of the Na+,K(+)-ATPase enzyme contributes to gentamicin-induced nephrotoxicity.

Acetylglucosaminidase↗

PubMed1992

Protein kinase C activity in rat renal proximal tubule cells.

The presence of protein kinase C (PKC) in proximal tubule cells of the rat kidney is established by means of immunodetection and by the demonstration of calcium- and phospholipid-dependent, staurosporine-inhibitable histone phosphorylation. The calcium-dependence of renal PKC is described. Maximal activation of the enzyme (178.2 and 258.8 pmol P1 mg-1 min-1 for cytosol and membrane respectively) was achieved with 5 microM of Ca2+. Phorbol 12, 13 dibutyrate (PDBu) translocated PKC from cytosol to membrane in a dose- and time-dependent fashion, while 4 alpha-phorbol 12,13-didecanoate produced no significant effect on translocation. Cytosolic PKC activity was compared in immature and mature tissues (10- and 40-day-old kidneys). Basal activity was found to be significantly higher (P less than 0.05) in immature cells (272.8 vs. 157.5 pmol Pi mg-1 min-1). PDBu at 10(-6) M for 15 min reduced immunoreactivity in the soluble fraction of both groups, which was accompanied by a significant decrease in kinase activity. We speculate that the high PKC activity in the infant kidney plays a role in cell growth.

Aging↗

PubMed1992

Regulation of glomerular angiotensin II receptor densities in renovascular hypertension: response to reduced sympathetic and vasopressin influence.

The regulation of the density of angiotensin II receptors in renal glomeruli in response to changes in salt intake is altered in Sprague-Dawley rats with renovascular hypertension due to aortic constriction, and in hypertensive salt-sensitive Dahl rats (Sahlgren 1989, Sahlgren & Aperia 1989). This study examines the modulatory role of sympathetic activity and arginine-vasopressin on angiotensin II receptors in hypertensive Sprague-Dawley rats with aortic constriction as well as in normotensive control rats. Denervation of the left kidney caused a 50% increase in the glomerular angiotensin II receptor density in the denervated kidney in both hypertensive rats and normotensive controls. An even more marked increase in glomerular receptor density occurred in both hypertensive rats and controls after blocking the sympathetic nervous system with guanethidine. To block the effects of arginine-vasopressin we used a blocker of the V1-receptors (predominant in vessels) and found an approximately 100% increase in the glomerular receptor density of angiotensin II in rats with aortic constriction. There was no reduction in blood pressure. Thus, on the receptor level the renin-angiotensin system is markedly influenced by the activity of other major pressor systems.

Animals↗

PubMed1992

Intracellular pH regulation in cultured renal proximal tubule cells in different stages of maturation.

This study examines the ontogeny of cellular pH regulation in renal proximal tubule cells (RPTC). RPTC from 8- to 40-day-old Sprague-Dawley rats (RPTC-8 to RPTC-40) were studied after 48 h of primary culture. Intracellular pH (pHi) was measured by quantitative fluorescence microscopy using 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. Recordings were made under basal conditions and after imposing a cytoplasmic alkalosis and acidosis using 15 mM NH4+ salt. The net recovery rate (dpHi/dt) from intracellular acidosis increases significantly between 10 and 12 days of age from 0.39 +/- 0.04 to 0.54 +/- 0.06 pH units/min (P < 0.05, n = 10 vs. 6). This increase can be completely accounted for by an increase in the rate of amiloride (100 microM)-inhibitable Na(+)-H+ exchange (0.29 +/- 0.04 vs. 0.42 +/- 0.05 pH units/min, P < 0.05, n = 6 vs. 6). The rate of Na(+)-H+ exchange increases similarly in RPTC-10 and RPTC-40 when the transmembrane Na+ gradient is increased by Na+ depleting the cells (48 and 49%, respectively). The amiloride-insensitive recovery is Na+ independent and insensitive to 4-acetamido-4'-isothiocyanostilbene-2-2'-disulfonic acid (SITS, 500 microM) (range 0.08-0.14 pH units/min). The net recovery rate from intracellular alkalosis is significantly lower in RPTC-10 than in RPTC-40 (0.16 +/- 0.02 vs. 0.28 +/- 0.02 pH units/min, P < 0.01, n = 4 vs. 5). SITS (500 microM) inhibits the recovery by 27 +/- 8 and 26 +/- 9%, respectively, whereas amiloride has no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

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