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A S Segal

Publications and source records attributed to A S Segal.

At least 19 recordsLinked to original sources
PubMed1995

A calcium-activated and nucleotide-sensitive nonselective cation channel in M-1 mouse cortical collecting duct cells.

We recently reported that M-1 mouse cortical collecting duct cells show nonselective cation (NSC) channel activity (Proc. Natl. Acad. Sci. USA 89:10262-10266, 1992). In this study, we further characterize the M-1 NSC channel using single-channel current recordings in excised inside-out patches. The M-1 NSC channel does not discriminate between Na+, K+, Rb+, Cs+, and Li+. It has a linear I-V relation with a conductance of 22.7 +/- 0.5 pS (n = 78) at room temperature. The Pcation/P(anion) ratio is about 60 and there is no measurable conductance for NMDG, Ca2+, Ba2+, and Mn2+. Cytoplasmic calcium activates the M-1 NSC channel at a threshold of 10(-6) M and depolarization increases channel activity (NPo). Cytoplasmic application of adenine nucleotides inhibits the M-1 NSC channel. At doses of 10(-4) M and 10(-3) M, ATP reduces NPo by 23% and 69%, respectively. Furthermore, since ADP (10(-3) M) reduces NPo by 93%, the inhibitory effect of adenine nucleotides is not dependent on the presence of a gamma-phosphoryl group and therefore does not involve protein phosphorylation. The channel is not significantly affected by 8-Br-cGMP (10(-4) M) or by cGMP-dependent protein kinase (10(-7) M) in the presence of 8-Br-cGMP (10(-5) M) and ATP (10(-4) M). The NSC channel is not sensitive to amiloride (10(-4) M cytoplasmic and/or extracellular) but flufenamic acid (10(-4) M) produces a voltage-dependent block, reducing NPo by 35% at depolarizing voltages and by 80% at hyperpolarizing voltages. We conclude that the NCS channel of M-1 mouse cortical collecting duct cells belongs to an emerging family of calcium-activated and nucleotide-sensitive nonselective cation channels. It does not contribute to amiloride-sensitive sodium absorption and is unlikely to be a major route for calcium entry. The channel is normally quiescent but may be activated under special physiological conditions, e.g., during volume regulation.

Animals↗
PubMed1995

Stimulation of chloride transport by cAMP in rat proximal tubules.

We have previously demonstrated that formate and oxalate stimulate transcellular Cl- absorption (JCl) in the rat proximal tubule by a mechanism involving DIDS-sensitive anion exchange across the luminal membrane and diphenylamine-2-carboxylate (DPC)-sensitive Cl- channels in the basolateral membrane. Recent evidence indicates cAMP activation of Cl- channels in apical and basolateral membranes of proximal tubule cells. We therefore tested the effect of cAMP on Cl- and fluid transport in rat proximal tubule studied by luminal and capillary microperfusion in situ. The luminal perfusate contained 5 mM HCO3- and 145 mM Cl-, and the capillary perfusate contained 25 mM HCO3- and 110 mM Cl-, simulating conditions in the late proximal tubule. Addition of 0.5 mM dibutyryl cAMP markedly stimulated fluid absorption (Jv) and JCl. Similar effects resulted from addition of forskolin (10 microM) to stimulate cAMP production. The increments in Jv and JCl due to dibutyryl cAMP were abolished when the Cl- channel blocker DPC (200 microM) was added to the capillary perfusate but not when it was added to the lumen. The increments in Jv and JCl due to dibutyryl cAMP were unaffected by luminal DIDS (100 microM), which abolishes the increments in Jv and JCl induced by addition of oxalate. In contrast, the increments in Jv and JCl due to dibutyryl cAMP were abolished by luminal 5-nitro-2-(3-phenylpropylamino)benzoate (NPPB; 10 microM), another Cl- channel blocker. Luminal NPPB had no effect on baseline Jv and JCl nor on the increments in Jv and JCl induced by addition of oxalate.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1994

A novel approach allows identification of K channels in the lateral membrane of rat CCD.

We have developed a novel approach to study K channels in the lateral membrane of principal cells (PC) in rat cortical collecting ducts (CCD). The technique consists of 1) exposing the CCD apical membrane, 2) removing the intercalated cells adjoining a PC by gentle suction through a pipette, and 3) applying patch-clamp technique to the lateral membrane of PC. Functional viability of the PC was confirmed by three indexes: 1) maintenance of physiological cell membrane potentials (-85 +/- 3 mV); 2) depolarization of the cell membrane potential with 1 mM Ba2+; and 3) hyperpolarization of the cell potential with 0.1 mM amiloride. Two types of K channels were identified: a low-conductance K channel and an intermediate-conductance K channel. In cell-attached patches the slope conductance of the low-conductance K channel was 27 pS and that of the intermediate-conductance K channel was 45 pS. The open probability (Po) of the 27-pS K channel was 0.81 +/- 0.02 and was not voltage dependent. In contrast, the Po of the 45-pS K channel was 0.23 +/- 0.01 at the spontaneous cell membrane potential and was increased by hyperpolarization. In addition, decrease of the bath pH from 7.4 to 6.7 reduced the 27-pS K channel current amplitude in a voltage-dependent manner, but the Po was not affected. Finally, two time constants were required to fit open- and closed-time histograms of both populations of K channels. Application of 1 mM Ba2+ completely blocked these K channels. We conclude that two types of K channel are present in the basolateral membrane of PC.

Amiloride↗
PubMed1992

Mouse cortical collecting duct cells show nonselective cation channel activity and express a gene related to the cGMP-gated rod photoreceptor channel.

Apical nonselective cation channels with an average single-channel conductance of 34 +/- 2.3 pS were found in M-1 mouse cortical collecting duct cells. Channel activity is increased by depolarization and abolished by cytoplasmic calcium removal. Cytoplasmic application of 0.1 mM cGMP decreases channel open probability by 27%. cDNAs corresponding to approximately 40% of the coding region of the photoreceptor channel were isolated by the polymerase chain reaction from M-1 cells and a rat kidney cDNA library. The rat kidney-derived sequence differs by a single base, and the M-1-cell-derived sequence differs by only two bases, from the photoreceptor sequence. A second clone from M-1 cells differs by 20 out of 426 bases from the photoreceptor sequence. In all three clones, the deduced amino acid sequence is identical to that of the rat photoreceptor channel. Northern blot analysis of poly(A)+ RNA from M-1 cells reveals the presence of a 3.2-kilobase band hybridizing with a retinal cGMP-gated cation channel probe. The results suggest the expression in M-1 cells of more than one gene coding for nonselective cation channels or channel subunits, one of which is identical to the cGMP-gated cation channel gene of rod photoreceptors.

Animals↗
PubMed1984

Electromagnetic dosimetry in a Crawford cell: 225 to 500 MHz.

A Crawford cell exposure chamber (main section 30 cm square) was used for electromagnetic dosimetry in the 225 to 500 MHz frequency range. Electric field patterns were measured within the cell. No higher-order modes were observed at any of the frequencies studied below 500 MHz, but significant field perturbations were seen at 2450 MHz. Energy absorption in a prolate spheroidal hamster phantom and in saline-filled spheres of various sizes was measured. The normalized whole-body specific absorption rate (SAR) in watts/kg per mW/cm2 increased from 0.11 (at 225 MHz) to 0.42 (at 450 MHz) for the hamster phantom in E polarization, from 0.06 (at 325 MHz) to 0.20 (at 500 MHz) for K polarization, and from 0.03 (at 325 MHz) to 0.12 (at 500 MHz) for H polarization. Although these values exceed predictions from the long-wavelength far-field approximation for power absorption, the measured SARs were corroborated directly using calorimetry. In addition, calorimetric data obtained using saline-filled spheres suggests that absorbed power in a Crawford cell converges to the far-field plane wave theoretical values only for objects occupying less than 20% of the vertical dimension from the septum to the outer wall.

Electromagnetic Fields↗
PubMedDate not supplied

[Prostaglandin E1 in the diagnosis and therapy of erectile disorders].

Intracavernous injections (ICI) of prostaglandin E1 (PGE1) of German produce (Schwarz Pharma A. G.) have been tested for diagnosis of erectile disorders in 63 patients (age 32-71, the majority at the age 45-65) and for autotherapy in 22 patients. In 76% of males with erectile impotency PGE1 ICI in a dose 10-20 micrograms result in marked erection which emerged within 5-15 min after the injection and persisted for 90 min on the average in spite of ejaculation. 86% of patients suffering from erectile dysfunction found this method of impotency correction satisfactory as it warrants normal coitus in 91% of cases (dose regimen 10-20 micrograms). ICI of PGE1 in the above dose 1-2 times a week for 2 months is safe, entail no systemic and insignificant local side effects. The risk of priapism and cavernous body fibrosis is minimal. The duration of the effect is related to the dose. The above advantages make PGE1 superior to papaverin and phentolamine. PGE1 ICI are recommended as the treatment of choice for therapy of erectile dysfunctions.

Adult↗