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D M Berman

Publications and source records attributed to D M Berman.

At least 19 recordsLinked to original sources
PubMed1996

GAIP and RGS4 are GTPase-activating proteins for the Gi subfamily of G protein alpha subunits.

A novel class of regulators of G protein signaling (RGS) proteins has been identified recently. Genetic evidence suggests that RGS proteins inhibit G protein-mediated signaling at the level of the receptor-G protein interaction or the G protein alpha subunit itself. We have found that two RGS family members, GAIP and RGS4, are GTPase-activating proteins (GAPs), accelerating the rate of GTP hydrolysis by Gi alpha 1 at least 40-fold. All Gi subfamily members assayed were substrates for these GAPs; Gs alpha was not. RGS4 activates the GTPase activity of certain Gi alpha 1 mutants (e.g., R178C), but not others (e.g., Q204L). The GAP activity of RGS proteins is consistent with their proposed role as negative regulators of G protein-mediated signaling.

Base Sequence↗
PubMed1995

Expression and regulation of steroid 5 alpha-reductase in the urogenital tract of the fetal rat.

Two androgens, testosterone and dihydrotestosterone, are required for the development of the male urogenital tract in the rat. Testosterone is secreted by the fetal testes and is thought to elicit differentiation of the Wolffian ducts into seminal vesicles, vas deferens, and epididymides. Testosterone is converted into dihydrotestosterone by steroid 5 alpha-reductase in the urogenital tract, and this conversion is necessary for the differentiation of the prostate and external genitalia. Genes encoding two 5 alpha-reductase isozymes, designated type 1 and type 2, have been identified. We examined the expression and regulation of these genes on days 17-21 in the urogenital tracts of male and female fetuses. Expression of the type 1 gene predominated in epithelial cells, whereas type 2 gene expression was limited to mesenchymal cells. Surprisingly, this expression pattern was detected in both testosterone-dependent and dihydrotestosterone-dependent anlagen of the urogenital tract and was the same in both male and female fetuses. Furthermore, transcripts encoding the two isozymes were present in their respective cell types before the overt differentiation of internal genitalia. Androgens stimulated expression of the type 2 gene in the urogenital tracts of both sexes, but did not effect expression of the type 1 gene or the cell type-specific expression patterns of the 5 alpha-reductase genes. In the adult prostate, 5 alpha-reductase gene expression is under feedforward control, in which the product of the enzyme, dihydrotestosterone, stimulates the expression of the gene. However, no evidence for feedforward regulation of either 5 alpha-reductase gene was detected in the fetus.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1994

Changes in membrane potential associated with cell swelling and regulatory volume decrease in barnacle muscle cells.

Our aim was to test the effect of hypotonicity and extracellular Ca2+ (Cao) on cell volume and membrane potential (VM) in barnacle muscle cells. Under isotonic conditions the resting VM of isolated cells mounted in the experimental chamber exposed to either Ca(2+)-free or Ca(2+)-containing (11 mM) solutions was -46.3 +/- 1.0 mV (n = 24) and -56.2 +/- 0.9 mV (n = 38), respectively. In the absence of Cao, the cells depolarized at a rate of 2.3 +/- 0.47 mV/hr; the presence of Cao reduced this rate of depolarization by 2.9-fold. Both in the absence or presence of Cao, the cells swelled in response to hypotonicity but underwent regulatory volume decrease (RVD) when Cao was present. Addition of the Ca2+ channel blocker, verapamil (0.1 mM), inhibited the Cao-dependent RVD. The percentage of cells responding with RVD increased with larger hypotonic challenges. There was a Cao-independent direct relationship between cell swelling and membrane depolarization which can be explained by dilution of the concentration of intracellular K+ ([K+]i). RVD was accompanied by a small hyperpolarization (3.0 +/- 0.38 mV/2 hr) which may represent increases in [K+]i during cell shrinking and activation of a conductive pathway. The results indicate the following: (1) the presence of Cao stabilizes VM; (2) cell swelling produces a depolarization which can be explained by dilution of [K+]i; (3) cell swelling activates a verapamil-sensitive Ca2+ influx responsible for promoting RVD; and (4) RVD is accompanied by a hyperpolarization which may result from activation of a conductive pathway.

Animals↗
PubMed1994

Ca2+ stores in smooth muscle cells: Ca2+ buffering and coupling to AVP-evoked inositol phosphate synthesis.

Cytosolic Ca2+ concentrations ([Ca2+]cyt) and [3H]inositol phosphates ([3H]InsP) were correlated while decreasing the Ca2+ content of sarcoplasmic reticulum (SR) stores in cultured A7r5 cells at rest and after activation with 8-arginine vasopressin (AVP). Decreasing Ca2+ influx by reducing extracellular Ca2+ or by treatment with verapamil had no effect on resting [Ca2+]cyt but significantly inhibited the AVP-evoked Ca2+ transients (delta Ca2+). Neither treatment affected basal [3H]InsP, but both treatments increased AVP-evoked synthesis of [3H]InsP. Likewise, basal [3H]InsP were unaffected by brief (10-30 s) exposures to thapsigargin (TG), while AVP-induced [3H]InsP synthesis was significantly augmented. Similar treatment with TG rapidly increased resting [Ca2+]cyt and decreased SR Ca2+ by 9-25% as manifested by decreased delta Ca2+. By contrast, ryanodine induced slow increases in [Ca2+]cyt that stabilized within 30 min; subsequent AVP-induced delta Ca2+ were attenuated by 50%. Ryanodine had no effect on either basal or stimulated [3H]InsP levels. Agents that elevate adenosine 3',5'-cyclic monophosphate (cAMP) such as caffeine, 8-bromo-cAMP, and forskolin inhibited AVP-evoked [3H]InsP formation. These observations provide further characterization of a communication pathway between the AVP-sensitive Ca2+ stores in the SR and the plasmalemmal enzyme system involved in the synthesis of inositol 1,4,5-trisphosphate. This pathway is manifested by an inverse relationship between the Ca2+ content of an AVP-sensitive, ryanodine-insensitive SR Ca2+ store and evoked [3H]InsP synthesis and may represent an important component in the tonic regulation of resting [Ca2+]cyt and vasoconstrictor- and hormone-evoked SR Ca2+ release.

Arginine Vasopressin↗
PubMed1994

Atrial natriuretic peptide inhibited the natriferic and hydrosmotic effects of arginine vasotocin on toad skin.

The effect of rat atrial natriuretic peptide (rANP) on hormonal stimulated osmotic water permeability (Jw, hydrosmotic effect) and net ion transport (short-circuit current, SCC, natriferic effect) was studied on toad skin, a tissue with functional similarities to the mammalian distal nephron, in order to assess actions on transport mechanisms. Rat atrial natriuretic peptide, rANP-99-126 (rANP) inhibited stimulated SCC and Jw to submaximal concentrations of arginine vasotocin (AVT) at a site before cyclic AMP generation. The angiotensin-converting enzyme inhibitor (ACEI) MK-422 did not modify the inhibitory effect of ANP in the stimulated Jw.

Animals↗
PubMed1993

Cell-type-specific expression of rat steroid 5 alpha-reductase isozymes.

The enzyme steroid 5 alpha-reductase (EC 1.3.99.5) is a component of an intercellular signaling pathway that determines cell fate in the primordium of the mammalian reproductive tract. During male phenotypic sexual differentiation, the dihydrotestosterone product of this enzyme binds to the androgen receptor and initiates development of the external genitalia and prostate. Genes encoding two isozymes of steroid 5 alpha-reductase with different biochemical properties and tissue distributions have recently been isolated. In the current study, we utilize in situ hybridization analysis to determine cell-type-specific expression patterns of the 5 alpha-reductase isozyme mRNAs in two androgen target tissues (regenerating ventral prostate and epididymis) and a peripheral tissue (liver). In regenerating ventral prostate, the type 1 mRNA is expressed in basal epithelial cells whereas expression of the type 2 mRNA is largely confined to stromal cells. These results were confirmed by immunohistochemical analysis and are consistent with distinct roles played by the isozymes in the prostate. In the epididymis, both 5 alpha-reductase isozyme mRNAs are expressed in epithelial cells. Only the type 1 mRNA is present in the liver. This mRNA is distributed in a striking spatial gradient extending from hepatocytes surrounding the portal triad (high expression) to those surrounding the central vein (low to absent expression). These findings demonstrate cell-type-specific expression of the steroid 5 alpha-reductase isozymes and underscore their distinct and overlapping functions in androgen physiology.

Animals↗
PubMed1993

Effects of angiotensin I of the American bullfrog Rana catesbeiana on amphibian tissues.

1. The effect of bullfrog angiotensin I [Asp1, Val5, Asn9] angiotensin I, (AT I) on short-circuit current (SCC) on isolated toad skin and aorta contractility was examined. 2. AT I increased SCC in toad skin, the effect was partially inhibited by angiotensin-converting enzyme inhibitor (ACEI) teprotide. 3. AT I induced contractile responses in isolated rings of toad aorta. This effect was partially inhibited by captopril and completely blocked by the peptide antagonist [Sar1, Ile8] angiotensin II. 4. Present results indicate that this homologue AT I would act in amphibian tissues by conversion to AT II.

Angiotensin I↗
PubMed1993

External Ca effect on water permeability, regulatory volume decrease, and extracellular space in barnacle muscle cells.

The effect of extracellular Ca2+ (Cao) on sarcolemmal hydraulic water permeability (L'p), regulatory volume decrease (RVD), and extracellular space (ECS) was studied in barnacle muscle cells. Absence or presence of Cao had no effect on L'p [0 Cao = 2.762 +/- 0.098 x 10(-5), and 11 mM Cao = 2.720 +/- 0.222 x 10(-5) cm.kg.s-1 x osmol x 1-kgH2O-1]. Likewise, cells exposed to anisosmotic media (for < 30 min) behaved as osmometers in 0 and 11 mM Cao, showing similar slopes and intercepts in van't Hoff plots. At longer incubation times, however, hyposmotic conditions promoted a Cao-dependent RVD. The relationship between Cao and the percentage of cells responding with RVD to a hyposmotic challenge was sigmoidal (half-maximal Cao = 4.83 mM). The mean rate of RVD (40 nl/min) was independent of the level of swelling in response to hyposmotic challenges. However, the magnitude of RVD increased with larger hyposmotic challenges. Both the presence of Cao and hypotonicity reduced the "apparent" ECS by 47 +/- 6 and 39 +/- 6%, respectively. Three-dimensional reconstruction of autoradiographs of the cells was made to interpret these results.

Animals↗
PubMed1992

Stored calcium modulates inositol phosphate synthesis in cultured smooth muscle cells.

Cytosolic Ca2+ concentrations ([Ca2+]cyt) and [3H]inositol phosphates ([3H]InsP) were correlated while varying the Ca2+ content of the sarcoplasmic reticulum (SR) in cultured A7r5 cells at rest and during activation with [Arg8]-vasopressin (AVP). Thapsigargin (TG) raised and superfusion with 0 Ca2+ lowered [Ca2+]cyt, but both treatments decreased SR Ca2+ and AVP-evoked Ca2+ transients. Neither TG nor 0 Ca2+ affected basal [3H]InsP, but both treatments increased AVP-evoked synthesis of [3H]InsP. Exposure for several minutes to 40 mM K+ solution, BAY K 8644, or low-Na+ solution all elevated [Ca2+]cyt and, thereby, increased SR Ca2+, as manifested by augmented AVP-evoked Ca2+ transients. In all three cases, AVP-evoked, but not basal, [3H]InsP were reduced. The inhibitory effect of 40 mM K+ on AVP-evoked [3H]InsP synthesis was blocked when SR Ca2+ uptake was prevented by TG. Brief (30-s) exposures to 40 mM K+, which elevated [Ca2+]cyt but not SR Ca2+ loading, did not modify AVP-evoked [3H]InsP synthesis or Ca2+ transients. These results demonstrate an inverse relationship between SR Ca2+ content and evoked [3H]-InsP synthesis. Moreover, they suggest that SR Ca2+ may serve as a signal that modulates sarcolemmal [3H]InsP formation.

Arginine Vasopressin↗
PubMed1992

On the mechanism of vasodilating action of berberine: possible role of inositol lipid signaling system.

We have studied the effect of the alkaloid berberine on the contraction of guinea pig aortic strips induced by various stimuli. Berberine (25-200 microM) inhibited the response of the strips to norepinephrine and histamine, but did not decrease the high K(+)-elicited contraction. The antagonism of berberine was not competitive because in the presence of the alkaloid, maximum response to agonists could not be obtained. Analysis of the drug's effect on the time course of norepinephrine-induced contraction showed that berberine reduced both the rate and the relative contribution to developed tension of the initial, rapid phase, whereas the slow, later component was less affected. Berberine inhibited the response of aortic strips incubated in 0 mM Ca++ to norepinephrine, but did not reduce caffeine-induced contraction and also inhibited phospholipase C-activated contractile response, which has been ascribed to production of inositol phosphate-3 in smooth muscle cells. In cultured arterial smooth muscle cells (A7r5 line), the alkaloid did not significantly decrease the production of inositol phosphates activated by Arg8-vasopressin. The pattern of berberine action is difficult to reconcile with an involvement of the contractile machinery and suggests that the drug has no effect on the voltage-operated calcium channels. Although an antagonism at the receptors or an increase of cyclic AMP or cyclic GMP cannot be completely excluded, we suggest that at least one component of the berberine inhibitory effect may be due to its action on some step of the chain of events linking receptors to contractile response.

Animals↗
PubMed1991

Deletion of steroid 5 alpha-reductase 2 gene in male pseudohermaphroditism.

The conversion of testosterone into dihydrotestosterone by steroid 5 alpha-reductase is a key reaction in androgen action, and is essential both for the formation of the male phenotype during embryogenesis and for androgen-mediated growth of tissues such as the prostate. Single gene defects that impair this conversion lead to pseudohermaphroditism in which 46X,Y males have male internal urogenital tracts, but female external genitalia. We have described the isolation of a human 5 alpha-reductase complementary DNA from prostate. Subsequent cloning and genetic studies showed that this gene (designated 5 alpha-reductase 1) was normal in patients with 5 alpha-reductase deficiency. We report here the isolation of a second 5 alpha-reductase cDNA by expression cloning and the polymerase chain reaction. The biochemical and pharmacological properties of this cDNA-encoded enzyme (designated 5 alpha-reductase 2) are consistent with it being the major isozyme in genital tissue. A deletion in this gene is present in two related individuals with male pseudohermaphroditism caused by 5 alpha-reductase deficiency. These results verify the existence of at least two 5 alpha-reductases in man and provide insight into a fundamental hormone-mediated event in male sexual differentiation.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1991

Characterization and chromosomal mapping of a human steroid 5 alpha-reductase gene and pseudogene and mapping of the mouse homologue.

The enzyme steroid 5 alpha-reductase catalyzes the conversion of testosterone into the more powerful androgen, dihydrotestosterone. We previously described the cloning of rat and human cDNAs that encode steroid 5 alpha-reductase and their expression in oocytes and cultured cells. Here, we report the isolation, characterization, and chromosomal mapping of two human steroid 5 alpha-reductase genes. One gene (symbol SRD5A1) is functional, contains five exons separated by four introns, and maps to the distal short arm of chromosome 5. Two informative restriction fragment length polymorphisms are present in exons 1 and 2 of this gene. A second gene (symbol SRD5AP1) has all of the hallmarks of a processed pseudogene and was mapped to the q24-qter region of the X chromosome. In the mouse, a single steroid 5 alpha-reductase gene (Srd5 alpha-1) is linked to Xmv-13 on chromosome 13.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗
PubMed1989

Trypsin affects basal and stimulated osmotic water permeability in isolated toad skin.

1. We investigated the effect of trypsin (Tryp) on basal, stimulated and fluphenazine (FPZ)-inhibited net water flow (Jw) through isolated toad skin (Bufo arenarum). 2. Epidermal Tryp (20 min) promoted an increase in basal Jw which was dose-dependent (maximal with 0.5 mg/ml) and was prevented by a Tryp inhibitor (SBTI). 3. Tryp treatment inhibited the subsequent response to substances known to act before (oxytocin, Oxy) or after cyclic AMP (cAMP) generation (theophylline). 4. Tryp-induced Jw was not additive with the maximal response to Oxy or theophylline and did not modify FPZ's inhibitory effect on stimulated Jw. 5. Dermal Tryp (0.5 mg/ml, 20 min) did not modify basal, but inhibited Oxy and isoproterenol-stimulated Jw, without altering the response to theophylline or db-cAMP. 6. Collectively, our results show a differential action for epidermal and dermal Tryp. Tryp's side-selective action enables its use as a pharmacological tool in the functional dissection of Jw across toad skin.

Animals↗
PubMed1989

Effect of rat cardionatrin I (rat ANF 99-126) on the response of toad skin to angiotensin II.

The atrial natriuretic peptide cardionatrin I (cardionatrin I is ANF 99-126) was used in studies directed to assess its effects on osmotic water permeability (Posm) and short-circuit current (SCC) in isolated toad skin. Results showed that ANF 99-126 (10(-7) M) added to the dermal side of the skin had no effect on basal Posm or SCC. However, ANF 99-126 (3.3 x 10(-8) M) was able to produce a 50% reversible inhibition of the maximal Posm response to angiotensin II (AII) (3.2 x 10(-8) M). These effects were seen when the skins were preincubated with ANF 99-126 for 10 min or less before the addition of AII. Longer preincubation appeared to inactivate ANF 99-126 through proteolysis. ANF 99-126(10(-7) M) failed to inhibit the SCC response to AII (10(-5) M) in toad skin. These results are compatible with a modulatory function for ANF on several systems including those involved in the regulation of extracellular fluid volume.

Angiotensin II↗
PubMed1988

Basal and amiloride-induced short-circuit current across isolated toad skin (Bufo arenarum).

We have previously demonstrated that amiloride (amil) addition to the isolated ventral pelvic (VPel) skin of Bufo arenarum toad induces negative short-circuit current values, which are equivalent to the isotopically measured net chloride transport. In the present work, we found that exposure of various regions of toad skin to amil yielded different values of short-circuit current (aSCC): negative aSCC was found in the VPel and ventral pectoral skin, while those of the dorsal one were not different from zero. The distinct values of aSCC found show a regional difference in the active chloride absorption, probably related to postural adaptations. A possible role of this adaptation would be related to chloride participation in the saline balance of the animals, or the maintenance of epithelial integrity.

Amiloride↗
PubMed1987

Reversed short-circuit current across isolated skin of the toad Bufo arenarum.

Short-circuit current (SCC) across isolated pelvic skin of the toad Bufo arenarum has been shown to be reflected by the algebraic sum of net sodium and chloride transport. After the animals had been maintained in tap water, amiloride--an apical sodium channel blocker--led to a reversal of potential difference (rPD) across this preparation, to which corresponded a reversed short-circuit current (rSCC). Both rSCC and rPD were abolished by dermal treatment of skins with the metabolic inhibitor dinitrophenol, or by omission of chloride ion from the Ringer solution bathing both sides of the skin. There was a significant positive correlation between rSCC and isotopically determined net chloride transport after amiloride. An inhibitory action of amiloride on unidirectional chloride fluxes was detected, but only early after drug addition. rSCC was absent in skins of toads exposed to 110 mmol/l NaCl in tap water during 10 days. Together, our results suggest that amiloride addition--by inhibiting active sodium movement--can in certain conditions reveal the existence of an inward active chloride transport.

Amiloride↗
PubMed1987

Comparative effects of angiotensin II on osmotic water permeability in the toad (Bufo arenarum).

The possible relationship between the renin-angiotensin system and water balance in the toad Bufo arenarum has been indirectly explored. A positive correlation was found between the hydrosmotic response of ventral pelvic toad skin to angiotensin II (A II) and some age indicators (body weight, snout-urostyle length or head width). A different hydrosmotic response for oxytocin and isoproterenol (but not for A II) was found between four cutaneous regions of toad body. We conclude that A II may not be directly involved in the regulation of water balance mediated by water absorption across the skin of Bufo arenarum toads.

Angiotensin II↗