PubMed Health⌕ Search

Biomedical subjects

B Ullrich

Publications and source records attributed to B Ullrich.

At least 19 recordsLinked to original sources
PubMed2003

Increased frequency of migraine in narcoleptic patients: a confirmatory study.

Previously we have reported an increased prevalence of migraine in narcoleptic patients. Because of the theoretical and clinical implications of this finding we recruited an independent new study sample of 100 patients with proven narcolepsy and conducted a structured 26-item interview based on the international diagnostic criteria for headache disorders, the Kiel Headache Questionnaire. Narcolepsy symptoms were measured by means of the Stanford Centre for Narcolepsy Sleep Inventory. Migraine prevalence was twofold to fourfold increased in the narcoleptic patients and amounted to 44.4% in women and 28.3% in men. The onset of narcolepsy symptoms was 12.3 +/- 11.4 years before the onset of migraine symptoms. The results might be regarded as indicative of a common pathophysiological pathway relevant to both of the two disorders.

Adult↗
PubMed2001

Failure of AH11110A to functionally discriminate between alpha(1)-adrenoceptor subtypes A, B and D or between alpha(1)- and alpha(2)-adrenoceptors.

The potency of the putatively alpha(1B)-adrenoceptor selective drug, 1-[biphenyl-2-yloxy]-4-imino-4-piperidin-1-yl-butan-2-ol (AH11110A), to antagonize contraction upon stimulation of alpha(1A)-adrenoceptors in rat vas deferens and rat perfused kidney, alpha(1B)-adrenoceptors in guinea-pig spleen, mouse spleen and rabbit aorta, and alpha(1D)-adrenoceptors in rat aorta and pulmonary artery was evaluated and compared to that of a number of subtype-discriminating antagonists. N-[3-[4-(2-Methoxyphenyl)-1-piperazinyl]propyl]-3-methyl-4-oxo-2-phenyl-4H-1-benzopyran-8-carboxamide (Rec 15/2739) and (+/-)-1,3,5-trimethyl-6-[[3-[4-((2,3-dihydro-2-hydroxymethyl)-1,4-benzodioxin-5-yl)-1-piperazinyl]propyl]amino]-2,4(1H,3H)-pyrimidinedione (B8805-033) were confirmed as selective for alpha(1A)-adrenoceptors, 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY 7378), 8-[2-(1,4-benzodioxan-2-ylmethylamino)ethyl]-8-azaspiro[4.5]decane-7,9-dione (MDL 73005EF), and cystazosin were found to be selective for alpha(1D)-adrenoceptors, whereas spiperone was weakly selective for alpha(1B)-over alpha(1A)-adrenoceptors. However, from the functional affinity profile obtained for AH11110A at alpha(1A)-adrenoceptors (pA(2)=6.41 in rat vas deferens), alpha(1B)-adrenoceptors (pA(2)=5.40-6.54) and alpha(1D)-adrenoceptors (pA(2)=5.47-5.48), the affinity and presumed selectivity previously obtained for AH11110A in radioligand binding studies at native alpha(1B)- and cloned alpha(1b)-adrenoceptors (pK(i)=7.10-7.73) could not be confirmed. Additionally, AH11110A enhanced the general contractility of rat vas deferens, produced a bell-shaped dose-response curve of vasodilation in perfused rat kidney, and its antagonism in most other tissues was not simply competitive. The affinity of AH11110A for prejunctional alpha(2)-adrenoceptors in rabbit vas deferens (pA(2)=5.44) was not much lower than that displayed for alpha(1)-adrenoceptor subtypes, revealing that AH11110A, besides alpha(1)-adrenoceptors, also interacts with alpha(2)-adrenoceptors, and thus may be unsuitable for alpha-adrenoceptor subtype characterization, at least in smooth muscle containing functional studies.

Adrenergic alpha-Agonists↗
PubMed2000

Trp42 rotamers report reduced flexibility when the inhibitor acetyl-pepstatin is bound to HIV-1 protease.

The Q7K/L331/L631 HIV-1 protease mutant was expressed in Escherichia coli and the effect of binding a substrate-analog inhibitor, acetyl-pepstatin, was investigated by fluorescence spectroscopy and molecular dynamics. The dimeric enzyme has four intrinsic tryptophans, located at positions 6 and 42 in each monomer. Fluorescence spectra and acrylamide quenching experiments show two differently accessible Trp populations in the apoenzyme with k(q1) = 6.85 x 10(9) M(-1) s(-1) and k(q2) = 1.88 x 10(9) M(-1) s(-1), that merge into one in the complex with k(q) = 1.78 x 10(9) M(-1) s(-1). 500 ps trajectory analysis of Trp X1/X2 rotameric interconversions suggest a model to account for the observed Trp fluorescence. In the simulations, Trp6/Trp6B rotameric interconversions do not occur on this timescale for both HIV forms. In the apoenzyme simulations, however, both Trp42s and Trp42Bs are flipping between X1/X2 states; in the complexed form, no such interconverions occur. A detailed investigation of the local Trp environments sampled during the molecular dynamics simulation suggests that one of the apoenzyme Trp42B rotameric interconversions would allow indole-quencher contact, such as with nearby Tyr59. This could account for the short lifetime component. The model thus interprets the experimental data on the basis of the conformational fluctuations of Trp42s alone. It suggests that the rotameric interconversions of these Trps, located relatively far from the active site and at the very start of the flap region, becomes restrained when the apoenzyme binds the inhibitor. The model is thus consistent with associating components of the fluorescence decay in HIV-1 protease to ground state conformational heterogeneity.

Acrylamide↗
PubMed1999

Buspirone functionally discriminates tissues endowed with alpha1-adrenoceptor subtypes A, B, D and L.

The affinity for functional alpha1-adrenoceptor subtypes of buspirone in comparison with its close structural analogs and selective alpha1D-adrenoceptor antagonists, BMY 7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]dec ane-7,9-dione) and MDL 73005EF (8-[2-(1,4-benzodioxan-2-ylmethylamino)ethyl]-8-azaspiro+ ++[4.5]decane-7,9-dione), was determined, namely at subtype A in rat vas deferens and perfused kidney, at subtype B in guinea-pig and mouse spleen, at subtype L in rabbit spleen, and at subtype D in rat aorta and pulmonary artery against noradrenaline-evoked contractions. BMY 7378 and MDL 73005EF were confirmed as 30- and 20-fold selective antagonists, respectively, for alpha1D- over both alpha1A- and alpha1B-adrenoceptors. Buspirone was a weak antagonist without intrinsic activity at alpha1A-adrenoceptors in rat vas deferens (pA2 = 6.12), at alpha1B-adrenoceptors in guinea-pig and mouse spleen (pA2 = 5.54 and 5.59) and at alpha1L-adrenoceptors in rabbit spleen (pA2 = 4.99), but caused partial vasoconstriction in rat kidney that was attenuable by the subtype D-selective adrenoceptor antagonist BMY 7378, but hardly by the subtype A-selective adrenoceptor antagonist B8805-033 ((+/-)-1,3,5-trimethyl-6-[[3-[4-((2,3-dihydro-2-hydroxymethyl)-1,4-be nzodioxin-5-yl)-1-piperazinyl]propyl]amino]-2,4(1H,3H)-pyrimidinedion e), confirming the additional presence of alpha1D-adrenoceptors mediating rat renal vasoconstriction. Buspirone behaved as a partial agonist at alpha1D-adrenoceptors in rat aorta (pD2 = 6.77, intrinsic activity (i.a.)= 0.40) and pulmonary artery (pD2 = 7.16, i.a. = 0.59). With buspirone as agonist in these tissues, the pA2 values of subtype-discriminating antagonists were consistent with their alpha1D-adrenoceptor affinity determined in rat aorta against noradrenaline and with published binding data on cloned alpha1d-adrenoceptors. The results provide pharmacological evidence that (1) in functional preparations for the A subtype, like rat vas deferens and perfused kidney, for the B subtype, like guinea-pig and mouse spleen, and for the L subtype, like rabbit spleen, buspirone is a weak antagonist without intrinsic activity, but (2) behaves as a partial agonist in rat aorta and pulmonary artery as models for the D subtype and (3) detects an additional vasoconstrictor alpha1D-adrenoceptor in rat kidney. Buspirone, like its close analogs BMY 7378 and MDL 73005EF, thus might also be a useful tool for functionally discriminating alpha1D- from alpha1A-, alpha1B- and alpha1L-adrenoceptors in various tissues.

Adrenergic Agonists↗
PubMed1998

[Affect and mimetic behavior].

The relationship between facial expression and experienced affect presents many problems. The two diametrically opposed positions proposing solutions to this problem are exemplified using the conceptions of Mandler u. Izard. The underlying premises of both conceptions still prevail in various forms. The authors reject the concepts according to which facial expression is merely correlated to the affects (see Mandler 1975) as well as the view that facial expression controls the affects (see Izard 1977). The relationship between affect and facial expression is reexamined, subjecting it to a semiotic, essentially semantic analysis similar to the Ogden and Richards' language and meaning approach. This analysis involves a critical discussion of Scherer's attempt of a purely communicational interpretation using Bühler's organon model. In the author's approach, facial expression is seen not simply as a system of signals, but as a system of representative signs which signify the affects and refer to the emotive meaning of things for the subject. The authors develop the thesis that human beings are not born simply with the ability to speak, but also with the abstract possibility of performing facial expressions. This ability develops by way of coordinating patterns of expressions, which are presumably phylogenetically determined, with affects that take on a socially determined individual form, similar to language acquisition during socialisation. The authors discuss the methodological implications arising for studies investigating the affective meaning of facial expressions.

Affect↗
PubMed1997

Contraction of guinea-pig gallbladder: muscarinic M3 or M4 receptors?

The muscarinic receptor mediating contraction of the guinea-pig isolated gallbladder, currently being disputed to belong either to the M3 or M4 subtype, was characterized by subtype-preferring agonists and discriminating antagonists. Highly significant correlations of agonist potencies to contract the gallbladder, e.g., arecaidine propargyl ester, oxotremorine, 5-methylfurtrethonium > arecoline, arecaidine 2-butyne-1,4-diyl bisester > (R)-nipecotic acid ethyl ester > 4-[[N-(4-chlorophenyl)carbamyl]oxy]-2-butynyltrimethylammonium iodide (4-Cl-McN-A-343), (S)-nipecotic acid ethyl ester > 4-[[N-(3-chlorophenyl)carbamoyl]oxy]-2-butynyltrimethylammonium chloride (McN-A-343) were found with muscarinic M3 receptors mediating contraction of the guinea-pig ileum and vasodilation in rat perfused kidney. Functional affinities at guinea-pig gallbladder muscarinic receptors of antagonists known to distinguish between native or cloned muscarinic M3/m3 and M4/m4 receptors, e.g., himbacine, methoctramine, mefurtramine, tripitramine, idaverine, zamifenacin and 11-[[4-[4-(diethylamino)butyl]-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyr ido(2,3-b)(1,4)benzodiazepin-6-one (AQ-RA 741), were consistent with those at guinea-pig ileal muscarinic M3 receptors but not with published data at recently defined muscarinic M4 receptors in rabbit anococcygeus muscle or at muscarinic M1 and M2 receptors in rabbit vas deferens. Antagonist affinities at guinea-pig gallbladder correlated also best with published binding data on native or cloned muscarinic M3/m3 receptors but not with those for muscarinic M4/m4 receptors. The agonist potencies and antagonist affinities suggest that smooth muscle contraction elicited by muscarinic stimuli in guinea-pig gallbladder is mediated by functional muscarinic M3 receptors.

Animals↗
PubMed1996

Structure and evolution of neurexophilin.

Using affinity chromatography on immobilized alpha-latrotoxin, we have purified a novel 29 kDa protein, neurexophilin, in a complex with neurexin l alpha. Cloning revealed that rat and bovine neurexophilins are composed of N-terminal signal peptides, nonconserved N-terminal domains (20% identity over 80 residues), and highly homologous C-terminal sequences (85% identity over 169 residues). Analysis of genomic clones from mice identified two distinct neurexophilin genes, one of which is more homologous to rat neurexophilin and the other to bovine neurexophilin. The first neurexophilin gene is expressed abundantly in adult rat and mouse brain, whereas no mRNA corresponding to the second gene was detected in rodents despite its abundant expression in bovine brain, suggesting that rodents and cattle primarily express distinct neurexophilin genes. RNA blots and in situ hybridizations revealed that neurexophilin is expressed in adult rat brain at high levels only in a scattered subpopulation of neurons that probably represent inhibitory interneurons; by contrast, neurexins are expressed in all neurons. Neurexophilin contains a signal sequence and is N-glycosylated at multiple sites, suggesting that it is secreted and binds to the extracellular domain of neurexin l alpha. This hypothesis was confirmed by binding recombinant neurexophilin to the extracellular domains of neurexin l alpha. Together our data suggest that neurexophilin constitutes a secreted glycoprotein that is synthesized in a subclass of neurons and may be a ligand for neurexins.

Amino Acid Sequence↗
PubMed1996

Characterization of vascular P2 purinoceptors in the rat isolated perfused kidney.

In isolated, constant-pressure perfused rat kidneys at basal vascular tone, injected P2 purinoceptor agonists evoked vasoconstriction (alpha, beta-methylene ATP > beta, gamma-methylene ATP > ATP-gamma-S > 2-methylthio ATP > ATP > ADP = UTP). In kidneys with raised tone, the nucleotides produced vasodilatation at low doses (2-methylthio ATP > ADP = ATP = ATP-gamma-S > UTP; alpha, beta-methylene ATP and beta, gamma-methylene ATP, inactive), and constriction at high doses (alpha, beta-methylene ATP > beta, gamma-methylene ATP > ATP-gamma-S > 2-methylthio ATP > ADP = ATP > UTP). Removal of the endothelium abolished the dilator responses to the agonists. NG-Nitro-L-arginine methylester (L-NAME, 5 x 10(-5) M) abolished vasorelaxation in response to 2-methylthio ATP, a response which could be restored by additional L-arginine (3 x 10(-3) M). Both vasodilatation and constriction due to the nucleotides remained unaffected by indomethacin (3 x 10(-6) M), S-(p-nitrobenzyl)-6-thioinosine (3 x 10(-5) M) and 8-phenyltheophylline (3 x 10(-6) M). Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 1-3 x 10(-6) M), inhibited vasoconstriction caused by alpha, beta-methylene ATP, 2-methylthio ATP and UTP, but not by ATP. Suramin (3 x 10(-5) M) caused a rightward shift of the dose-response curves for constriction caused by alpha, beta-methylene ATP (27-fold) and 2-methylthio ATP (5-fold), whereas the ATP curve was shifted to the left (20-fold). With Evans blue (10(-5) M), vasodilatation due to the nucleotides was abolished and the dose-response curves for vasoconstriction caused by ATP and UTP were shifted left more than 100-fold, the effect to both could not be antagonized by PPADS (3 x 10(-6) M). These results suggest: (1) the different rank orders of P2 purinoceptor agonist potencies for constrictor and dilator responses in perfused rat kidney are consistent with mediation via P2x and P2Y purinoceptors, respectively; (2) P2X purinoceptors, selectively sensitive to blockade by PPADS, are located on vascular smooth muscle; (3) endothelial P2Y purinoceptor stimulation results in vasodilatation involving NO synthesis but not release of prostanoids; (4) Evans blue, which appears to combine selective P2Y purinoceptor blockade and strong inhibition of ecto-nucleotidases, potentiates vasoconstriction in response to the degradable nucleotides, ATP, 2-methylthio ATP and UTP; (5) additionally, Evans blue unmasks a PPADS-insensitive P2U purinoceptor where the nearly equipotent nucleotides, ATP and UTP, can produce vasoconstriction.

Adenosine Triphosphate↗
PubMed1996

[Remembering and acting out].

In the accompanying paper two fifteen-hour psychoanalytical therapies were investigated with regard to the temporal distribution of Luborskian relationship episodes and the facial expressions of both protagonists. The two therapies were taken from a sample of eleven treatments: one had had the most success; the other, the least. The investigation focussed on what type of interaction between the recollective narration of past relationships and the present form of relationships could be expected, and whether the relation between these two would be dependent upon the success of the therapy. The hypothesis that a parallel processing of the narrated episode and the exhibited emotion would occur within the patient could not be confirmed. The frequency of recollective narration correlated negatively--in line with a hypothesis of Freud's--with the frequency of exhibited emotions. In the successful treatment, however, the therapist exhibited the emotions which one would have expected the patient to show. The results are discussed in terms of a theory of the psychotherapeutical process and containing.

Acting Out↗
PubMed1995

Ca(2+)-dependent and -independent activities of neural and non-neural synaptotagmins.

Synaptotagmins (Syts) are brain-specific Ca2+/phospholipid-binding proteins. In hippocampal synapses, Syt I is essential for fast Ca(2+)-dependent synaptic vesicle exocytosis but not for Ca(2+)-independent exocytosis. In vertebrates and invertebrates, Syt may therefore participate in Ca(2+)-dependent synaptic membrane fusion, either by serving as the Ca2+ sensor in the last step of fast Ca(2+)-triggered neurotransmitter release, or by collaborating with an additional Ca2+ sensor. While Syt I binds Ca2+ (refs 10, 11), its phospholipid binding is triggered at lower calcium concentrations (EC50 = 3-6 microM) than those required for exocytosis. Furthermore, Syts bind clathrin-AP2 with high affinity, indicating that they may play a general role in endocytosis rather than being confined to a specialized function in regulated exocytosis. Here we resolve this apparent contradiction by describing four Syts, three of which (Syt VI, VII and VIII) are widely expressed in non-neural tissues. All Syts tested share a common domain structure, with a cytoplasmic region composed of two C2 domains that interacts with clathrin-AP2 (Kd = 0.1-1.0 nM) and with neural and non-neural syntaxins. The first C2 domains of Syt I, II, III, V and VII, but not of IV, VI or VIII, bind phospholipids with a similar Ca(2+)-concentration dependence (EC50 = 3-6 microM). The same C2 domains also bind syntaxin as a function of Ca2+ but the Ca(2+)-concentration dependence of Syt I, II and V (> 200 microM) differs from that of Syt III and VII (< 10 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Neuroligin 1: a splice site-specific ligand for beta-neurexins.

Neurexins are neuronal cell surface proteins with hundreds of isoforms generated by alternative splicing. Here we describe neuroligin 1, a neuronal cell surface protein that is enriched in synaptic plasma membranes and acts as a splice site-specific ligand for beta-neurexins. Neuroligin 1 binds to beta-neurexins only if they lack an insert in the alternatively spliced sequence of the G domain, but not if they contain an insert. The extracellular sequence of neuroligin 1 is composed of a catalytically inactive esterase domain homologous to acetylcholinesterase. In situ hybridization reveals that alternative splicing of neurexins at the site recognized by neuroligin 1 is highly regulated. These findings support a model whereby alternative splicing of neurexins creates a family of cell surface receptors that confers interactive specificity onto their resident neurons.

Alternative Splicing↗
PubMed1995

Differential distributions of novel synaptotagmins: comparison to synapsins.

Synaptotagmins and synapsins are prototypical synaptic vesicle proteins that are regulated by Ca2+: Synaptotagmins directly via Ca2+ binding, and synapsins indirectly via phosphorylation by Ca(2+)-dependent protein kinases. Recently, a bewildering multiplicity in the expression of isoforms of these proteins has become apparent. Thus, mammalian brains express at least 8 isoforms of synaptotagmin and 4 isoforms of synapsin if variants arising by differential splicing are included. We have now used in situ hybridization to determine the relative localization of the expression of multiple isoforms of synapsins and synaptotagmins to complement previous studies on their distribution. Our results demonstrate that almost all brain regions co-express all four synapsins at similar levels, suggesting that they are not functionally alternative but complementary. The different isoforms of synaptotagmin exhibit two distinct expression patterns: synaptotagmins that are expressed in a highly differential manner (synaptotagmins I, II and VI), and synaptotagmins with a relatively even distribution of expression similar to synapsins (synaptotagmins III, IV and VII). Our data are consistent with a functional specialization of synaptic vesicle protein isoforms that could result in differential properties of the respective classes of neurons that express them.

Animals↗
PubMed1995

Cartography of neurexins: more than 1000 isoforms generated by alternative splicing and expressed in distinct subsets of neurons.

Neurexins, a family of cell surface proteins specific to brain, are transcribed from two promoters in three genes, resulting in three alpha- and three beta-neurexins. In situ hybridization revealed differential but overlapping distributions of neurexin isoforms in different classes of neurons. PCRs demonstrated that alpha-neurexins are alternatively spliced at five canonical positions, and beta-neurexins at two. Characterization of many independent bovine neurexin I alpha cDNAs suggests that different splice sites are used independently. This creates the potential to express more than 1000 distinct neurexin proteins in brain. The splicing pattern is conserved in rat and cow. Thus, in addition to somatic gene rearrangement (immunoglobulins and T cell receptors) and large gene families (odorant receptors), alternative splicing potentially represents a third mechanism for creating a large number of cell surface receptors that are expressed by specific subsets of cells.

Alternative Splicing↗
PubMed1994

Synaptic targeting domains of synapsin I revealed by transgenic expression in photoreceptor cells.

Synapsins are abundant nerve terminal proteins present at all synapses except for ribbon synapses, e.g. photoreceptor cell synapses. Multiple functions have been proposed for synapsins, including clustering of synaptic vesicles and regulation of synaptic vesicle exocytosis. To investigate the physiological functions of synapsin and to ascertain which domains of synapsin are involved in synaptic targeting in vivo, we expressed synapsin Ib and its N- and C-terminal domains in the photoreceptor cells of transgenic mice. In these cells synapsin Ib is targeted efficiently to synaptic vesicles but has no significant effect on the development, structure or physiology of the synapses. This suggests that synapsin I does not have dominant physiological or morphoregulatory functions at these synapses. Full-length synapsin Ib and the N-terminal domains of synapsin Ib but not its C-terminal domains are transported to synapses, revealing that the molecular apparatus for synaptic targeting of synapsins is also present in cells which form ribbon synapses that normally lack synapsins. This apparatus appears to utilize the conserved N-terminal domains that are shared between all synapsins.

Animals↗
PubMed1994

Functional properties of multiple synaptotagmins in brain.

At least four forms of synaptotagmin are expressed in neurons. Of these, synaptotagmin I has an essential function in mediating Ca(2+)-triggered neurotransmitter release at hippocampal synapses, but the functional implications of multiple synaptotagmins are unknown. Synaptotagmins I-III exhibit a strikingly differential distribution between synapses, with most neurons coexpressing either synaptotagmins I or II with III. Synaptotagmin IV is present uniformly throughout the brain at low levels. Synaptotagmins III and IV are both coexpressed with synaptotagmin I in hippocampal synapses, suggesting that these synaptotagmins are not functionally redundant. The first C2 domains of synaptotagmins I-III exhibit similar Ca2+ affinities in phospholipid-binding assays, whereas that of synaptotagmin IV is unable to bind Ca2+. All synaptotagmins tested bind the clathrin-adaptor protein AP-2 with high affinity. Our results suggest that different synaptotagmins serve distinct but overlapping functions in neuronal membrane traffic, with synaptotagmins I and II representing alternative Ca2+ sensors in exocytosis and all synaptotagmins functioning as AP-2 receptors in endocytosis.

Adaptor Proteins, Vesicular Transport↗
PubMed1994

Distribution of synaptic markers in the retina: implications for synaptic vesicle traffic in ribbon synapses.

Synapses in the retina are present in two layers that can easily be distinguished morphologically: the thin outer plexiform layer (OPL) containing the photoreceptor ribbon synapses, and the more complex inner plexiform layer (IPL) containing mostly conventional synapses. In the current study we have used the exquisite spatial separation between ribbon and conventional synapses in the retina to investigate by immunocytochemistry the protein components of these two types of synapses. Our results show that all of the synaptic vesicle proteins tested are present in the ribbon synapses of photoreceptors except for the synapsins which were previously described to be absent from ribbon synapses. Thus, synaptic vesicles of ribbon and conventional synapses are likely to be very similar molecularly in spite of their different modes of trafficking. Furthermore, proteins with a likely function in synaptic vesicle docking and fusion (SNAP-25, munc-18) and endocytosis (dynamin) were also highly enriched in ribbon synapses, indicating that the basic machineries for synaptic membrane traffic are similar in ribbon and conventional synapses. Interestingly, photoreceptor cells contained only low concentrations of syntaxin I (which functions in the synaptic vesicle fusion complex) and GDI (which regulates the membrane association of rab-proteins as a function of GTP/GDP binding). These results raise the possibility that photoreceptors express other isoforms of these proteins, or that the functions of these proteins are not required for the tonical release mode of their synapses.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗