Phosphatase inhibitors increase the open probability of ENaC in A6 cells.

We studied the cellular phosphatase inhibitors okadaic acid (OKA), calyculin A, and microcystin on the epithelial sodium channel (ENaC) in A6 renal cells. OKA increased the amiloride-sensitive current after approximately 30 min with maximal stimulation at 1-2 h. Fluctuation analysis of cell-attached patches containing a large number of ENaC yielded power spectra with corner frequencies in untreated cells almost two times as large as in cells pretreated for 30 min with OKA, implying an increase in single channel open probability (P(o)) that doubled after OKA. Single channel analysis showed that, in cells pretreated with OKA, P(o) and mean open time approximately doubled. Two other phosphatase inhibitors, calyculin A and microcystin, had similar effects on P(o) and mean open time. An analog of OKA, okadaone, that does not inhibit phosphatases had no effect. Pretreatment with 10 nM OKA, which blocks protein phosphatase 2A (PP2A) but not PP1 in mammalian cells, had no effect even though both phosphatases are present in A6 cells. Several proteins were differentially phosphorylated after OKA, but ENaC subunit phosphorylation did not increase. We conclude that, in A6 cells, there is an OKA-sensitive phosphatase that suppresses ENaC activity by altering the phosphorylation of a regulatory molecule associated with the channel.

[Limits of parathyroid scintigraphy before surgery for hyperparathyroidism of renal origin]. / Limites de la scintigraphie parathyroïdienne avant chirurgie pour hyperparathyroïdisme d'origine rénale (51 cas).

AIM OF THE STUDY: To evaluate the results of parathyroid scinti scans (sestamibi or tetrofosmin) for detection of hyperplastic parathyroid glands responsible for renal hyperparathyroidism. METHODS: Injection of 15 mCi sestamibi or tetrofosmin and gammacamera acquisition of images focused on neck and mediastinum, 20 minutes and 2 hours thereafter. Injection of 150 mCi Iodine 123, acquisition of images 2 hours afterwards and visual subtraction. PATIENTS: 51 patients with renal insufficency or renal transplant were referred for surgical treatment of hyperparathyroidism. 52 scintiscans (sestamibi n = 19, tetrofosmin n = 33) were performed before operation (subtotal parathyroidectomy, bilateral thymectomy and parathyroid tissue cryopreservation). RESULTS: 180 hyperplastic parathyroid glands were resected, 71 of which had been detected by scintiscan. The factors modifying the results were the weight of the resected lesion and reoperation. All hyperplastic glands were detected in only 1 out of 41 scintiscans performed before first hand operations, whereas all missed glands were imaged in 8 out of the 10 explorations performed before reoperation for persistent renal hyperparathyroidism. The radionuclide, the type of hyperparathyroidism, the parathyroid location, patient's age and gender did not influence the results. No false-positive result was observed. CONCLUSION: Parathyroid scintiscan should not be routinely performed before the first neck exploration for renal hyperparathyroidism. It is mandatory in those cases needing reoperation for recurrent disease.

The effect of racemic ketamine on the large conductance Ca(+2)-activated potassium (BK) channels in GH3 cells.

Recently, inhalation anesthetics have been reported to block BK channels in adrenal chromaffin cells. To determine if BK block was characteristic only of inhalation anesthetics or was also a property of other general anesthetics we examined the effects of ketamine, an intravenous general anesthetic which is structurally different than inhalation anesthetics. Cell-attached and excised patch single channel and standard whole cell recording techniques were used to examine the effect of racemic ketamine on the BK channel activity in GH3 cells. When solutions containing 150 mM KCl are used in both the pipette and bath, the BK channels are characterized as a voltage-dependent channel with a unit conductance of 150-300 pS. Racemic ketamine (at clinically relevant concentrations; 2-500 microM) selectively blocked BK channels in a dose-dependent, reversible manner as evidenced by decreases in NPo (number of channels x open probability). This decrease was due to both a decrease in mean open time and an increase in the mean closed time but without a decrease in single-channel current amplitude. Ketamine shifts the Po vs voltage curve to higher potentials without a change in the slope of the voltage dependence. Ketamine also shifts the Po vs [Ca+2] relationship to higher Ca+2 concentrations. The IC50 for the single-channel block by ketamine is 20.3 +/- 15.9 microM. In an effort to confirm that the effect of ketamine was predominantly due to a block of the BK channels, standard whole cell techniques were utilized.(ABSTRACT TRUNCATED AT 250 WORDS)

Tyrosine kinase regulates epithelial sodium transport in A6 cells.

Insulin increases epithelial Na+ reabsorption, and many of its actions involve tyrosine kinase. We used tyrosine kinase inhibitors to examine the role of tyrosine kinase in the action of insulin. Pretreatment of Na+ transporting cells with tyrosine kinase inhibitors attenuates the subsequent action of insulin, suggesting that the action of insulin on epithelial Na+ transport involves tyrosine kinase activity. In addition to their effect on insulin-induced Na+ transport, the tyrosine kinase inhibitors also significantly reduce Na+ transport in Na(+)-transporting epithelial cells, suggesting that there is a significant tonic tyrosine kinase activity that modulates epithelial Na+ transport. Using patch-clamp methods, we found that one inhibitor, genistein, reduces the number of active Na+ channels in cell-attached patches without significantly affecting the open probability of any remaining channels. The effects of the tyrosine kinase inhibitors are not due to inhibition of protein kinase A (PKA), since H89, a PKA inhibitor, does not affect Na+ transport of control cells (as the tyrosine kinase inhibitors do), and the tyrosine kinase inhibitor, genistein or tyrphostin 23, does not alter the stimulation of ion transport by 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate, a membrane-permeable adenosine 3',5'-cyclic monophosphate analogue (as H89 does).

Regulation of renal epithelial sodium channels.

The high selectivity, low conductance, amiloride-blockable, sodium channel of the mammalian distal nephron (i.e. cortical collecting tubule) is the site of discretionary regulation which allows maintainance of total body sodium balance. In order to understand the physiological events that participate in this regulation, we have used the patch-clamp technique which allows us to measure individual Na+ channel currents and permits access to the cytosolic side of the channel-protein as well as its associated regulatory components. Most of our experiments have utilized the A6 amphibian renal cell line, which when grown on permeable supports is an excellent model for the mammalian distal nephron. Different mechanisms have been examined: (1) regulation by hormonal factors such as Anti-Diuretic Hormone (ADH) and aldosterone, (2) regulation by G-proteins, (3) modulation by protein kinase C (PK-C), and (4) modulation by products of arachidonic acid metabolism. Consistent with noise analysis of tight epithelial tissues, ADH treatment increased the number of active channels in apical membrane patches of A6 cells, without any apparent change in the open probability (Po) of the individual channels. Agents that increased intracellular cAMP mimicked the effects of ADH. In contrast, aldosterone was found to act through a dramatic increase in Po rather than through changes in channel density. Inhibition of methylation by deazaadenosine antagonizes the stimulatory effect of aldosterone. In excised inside-out patches GTP gamma S inhibits channel activity, whereas GDP beta S or pertussis toxin stimulates activity suggesting regulatory control by G-proteins. PK-C has been shown to contribute to 'feed-back inhibition' of apical Na+ conductance in tight epithelia.(ABSTRACT TRUNCATED AT 250 WORDS)

Potassium and chloride conductances in rat Leydig cells: effects of gonadotrophins and cyclic adenosine monophosphate.

1. The effects of gonadotrophins (luteinizing hormone and human chorionic gonadotrophin) and cyclic AMP on ionic conductances were investigated using the tight-seal whole-cell recording technique in Leydig cells freshly isolated from nature rat testis by enzymatic treatment. 2. In resting cells, the predominant ionic conductance is a voltage-dependent K+ conductance resembling the delayed rectifier K+ conductance of T-lymphocytes. This conductance is characterized by: (1) a time-dependent inactivation for potentials more positive than +20 mV, (2) a reversal potential near -65 mV, (3) a sensitivity to intracellular Cs+, and (4) a sensitivity to extracellular TEA and 4-aminopyridine. 3. A Cl- conductance is also present resembling the Cl- background conductance in squid axons and heart cells. In resting cells, this conductance contributes only a small component of the total outward current obtained with depolarizing pulses. 4. Gonadotrophins (human chorionic gonadotrophin, porcine luteinizing hormone and ovine luteinizing hormone) have little effect on the K+ conductance. They transiently increase a Cl- conductance after a delay of up to 30 s. This response does not occur if the hormones are applied late in the whole-cell recording. Gonadoliberine (GnRH) does not affect the Cl- or K+ conductance. 5. Internal cyclic AMP (100 microM) mimics all these effects while internal application of a GTP-ATP mixture induces a similar response, which is, however, sustained rather than transient. 6. The Cl- conductance was studied quantitatively with a GTP-ATP internal solution. This conductance is activated by depolarizing voltage steps to test potentials of -40 mV or more. Under these conditions, the instantaneous current observed as soon as the depolarizing pulse is applied displays outward rectification and reverses near ECl. During the pulses, a strong inactivation is observed for potentials greater than +40 mV. This conductance is independent of external and internal calcium. 7. It is concluded that the gonadotrophins act through a cyclic AMP-dependent process to activate a Cl- conductance. This conductance is different to the hyperpolarization-activated Cl- conductance and the calcium-activated Cl-conductance also present in the membrane of resting cells.

Electrophysiological studies of the action of gonadotropins on Leydig and Sertoli cells from rat testis.

Using intracellular microelectrode recordings, it was observed that FSH caused the hyperpolarization of cultured Sertoli cells from the testis of 17-day old rats; this hyperpolarization was related to the activation of a Na/K pump and an increase in Na/Ca influx and K efflux. The effect was irreversible and mediated by cAMP. Some other results suggested an initial effect of FSH on the junctional complex between the Sertoli cells and then its calcium dependence. Voltage-clamped membrane currents were investigated from whole-cell patch clamp recordings performed on single Leydig cells isolated from adult rat testis. Two outward currents were evoked by depolarizing voltage steps: a potassium current recorded in cells dialyzed with low-calcium media (10(-9)-10(-8) M) and a chloride current recorded in cells dialyzed with high-calcium media (10(-7)-10(-6) M). These responses to modifications of intracellular calcium were not affected by hCG. However, this hormone induced an early change of the K current to a Cl current when the cells were dialyzed by a low-buffered EGTA-calcium medium. These results suggest that hCG stimulation involved the blockade of a potassium current and the activation of a chloride current through an increase of intracellular calcium.

Ca-dependent-chloride and potassium currents in rat Leydig cells.

Voltage-clamped membrane currents have been investigated from whole-cell patch-clamp recordings performed on single Leydig cells isolated from the adult rat testis. Two outward membrane currents were evoked by depolarizing voltage steps. A potassium current was recorded in cells dialyzed with low (10(-9)-10(-8) M) calcium media. This current was decreased by TEA (10 mM). A chloride current was recorded in cells dialyzed with high (10(-7)-10(-6) M) calcium media. This current was decreased by an external exposure to glutamate. Comparison of the currents at low and high internal calcium concentrations suggests that an increase of the intracellular calcium activates a chloride current.

[Specific renal lesions revealing the presence of sarcoidosis (author's transl)]. / L'atteinte rénale spécifique révélatrice de la sarcoïdose.

Three cases of granulomatous nephropathy are reported. In two patients this was definitely related to a true renal sarcoidosis, while the third case raised the problem of the significance of an "isolated sarcoidosis nodule". The authors discuss the frequency, clinical symptoms, and pathological appearances of these renal lesions which reveal the presence of sarcoidosis, as well as the relationship between renal insufficiency and the parenchymatous lesions observed, and therapy.