Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.24.3 (collagenase)
 18,340 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The properties of the low threshold Ca current (ICaT) in bullfrog (Rana catesbeiana) isolated atrial cardiomyocytes were studied using the whole-cell recording patch-clamp technique and compared with those of the high threshold Ca current (ICaL). In 91% of atrial cells we observed both ICaT and ICaL when collagenase and trypsin were used to dissociate the cells. But when pronase was used, only 30% of the cells exhibited ICaT. ICaT was never found in ventricular cells. ICaT could be investigated more easily when ICaL was inhibited by Cd ions (50 microM). Its kinetics were unchanged by substituting Ba for Ca, or in the presence of high concentrations of Ba. Both ICaT and ICaL exhibited reduced inactivation after high depolarizing prepulses. ICaT was found to be sensitive to dihydropyridines: 1 microM nifedipine decreased this current while 1 microM BAY K 8644 increased it; this occurred without significant variations in the steady-state inactivation curve. ICaT was more sensitive than ICaL to alpha 1-adrenergic and P2-purinergic stimulations, while ICaL was more sensitive to beta-adrenergic stimulation. Isoproterenol was still able to increase ICaT in the presence of high intracellular cAMP. Both currents were increased by 1 microM ouabain (although ICaL only transiently) and decreased by 10 microM ouabain. It is concluded that the two types of Ca channels can be observed in bullfrog atrial cells and that they are specifically altered by pharmacological agents and neuromediators. This may have implications for cardiac behavior.
J Gen Physiol 1992 Sep
PMID:Properties of the low threshold Ca current in single frog atrial cardiomyocytes. A comparison with the high threshold Ca current. 127 97

For continued studies of GnRH receptor regulation in the winter flounder, we have developed an in vitro system consisting of cultured pituitary cells dissociated by collagenase. Using immunocytochemical staining methods for gonadotropin, growth hormone, and prolactin, these cell types were represented at the levels of 25, 20, and 19.5% of total pituitary cell population, respectively. Receptors for GnRH were characterized in intact monolayered attached pituitary cells, maintained in RPMI culture medium. The cell GnRH receptor characteristics were compared with those previously described using pituitary homogenates. The cells were capable of binding GnRH in a similar manner on Day 2 or Day 3 of culture, indicating the integrity of GnRH receptors. The specificity of binding was demonstrated since only high doses of cold GnRHa competed with 125I-GnRHa uptake, different peptides being without effect. The specific binding is saturable and the data suggest the presence of a single class of high-affinity (apparent Ka = 1.50 x 10(9) M-1), high-capacity sites (binding capacity = 25.03 fmol/2.5 x 10(5) cells or 242.23 x 10(3) sites/gonadotroph) which is in accordance with the characteristics of GnRH receptors present in homogenates of pooled male and female pituitary glands. All these observations suggest that such an in vitro pituitary cell system would be appropriate for studying GnRH receptor characteristics under different physiological conditions.
Gen Comp Endocrinol 1992 Jan
PMID:Evidence of GnRH receptors in cultured pituitary cells of the winter flounder (Pseudopleuronectes americanus W.). 131 5

Rainbow trout hepatocytes isolated by collagenase perfusion were suspended in primary culture for up to 72 hr at 11 degrees and then the microsomal L-thyroxine (T4) 5'-monodeiodinase (5'D) activity was evaluated by 125I- generation from [125I]T4. The 5'D activity and Vmax (level of functional enzyme) and Km (Michaelis-Menten constant) values for microsomes obtained from incubated hepatocytes corresponded to those for microsomes obtained directly from intact livers. HPLC analysis revealed 3,5-[125I]3'-triiodo-L-thyronine (T3) as the only significant 125I-labeled organic product. Hepatocyte survival ( > 90%) and 5'D activity were unaltered by insulin (10(-9) M) in the incubate, but 5'D activity was inhibited by 10% fetal calf serum. Human growth hormone (hGH) at concentrations of 5-250 ng/ml did not increase 5'D activity. These results do not support previous in vivo studies demonstrating hGH-enhanced hepatic 5'D function in trout and indicate that either hGH acts indirectly on the liver to enhance 5'D activity or incubated hepatocytes lose GH responsiveness. However, coincubation of hepatocytes with T3 (15 or 30 nM) for 24 hr inhibited 5'D activity in a dose-dependent manner and induced the production of 3-[125I]3',5'-triiodo-L-thyronine (reverse T3). These data support previous in vivo studies in showing that T3 autoregulates its own hepatic production and show that T3 does so by acting directly on the hepatocyte to modify deiodination pathways.
Gen Comp Endocrinol 1992 Nov
PMID:Thyroxine 5'-monodeiodinase activity in microsomes from isolated hepatocytes of rainbow trout: effects of growth hormone and 3,5,3'-triiodo-L-thyronine. 147 36

We have detected the presence of nuclear 3,5,3'-triiodothyronine (T3) receptors in primary cultures of chick embryo hepatocytes and neurons. Hepatocytes were isolated from livers of embryos of 12, 16 and 19 days by treatment with 0.2% collagenase and hyaluronidase. They were plated at a density of 3-4 x 10(5)/35-mm petri dish in Ham's F-10 medium containing fetal calf serum, tryptose phosphate, and antibiotics. Cells were used for the binding assay at Day 3 of culture. Neurons from 8-day-old embryo brains were cultured in a serum-free medium at a density of 1.2 x 10(6) cells/35-mm petri dish and used for the binding assay after 7 days of culture. Biological activity of hepatocytes was determined by measuring insulin binding, inositol phosphate formation, and 5'-monodeiodinase activity. Neurons or glial cells in culture were identified by immunostaining with anti-neurofilaments and anti-glial fibrillary acidic protein antisera. Binding assay was performed with isolated nuclei and 0.4 M NaCl nuclear extracts. With the latter preparation, the Scatchard analysis showed, in both cells, a single, high-affinity, low-capacity T3 receptor. In the hepatocytes of 12-, 16-, and 19-day-old embryos association constants (Ka) were, respectively, 0.93 +/- 0.02, 0.74 +/- 0.03, and 0.56 +/- 0.04 nM-1, whereas the maximal binding capacities (MBC) were 2.26 +/- 0.2, 2.72 +/- 0.33, and 1.83 +/- 0.19 fmol/microgram DNA (mean +/- SE, n = 3). In neurons Ka was 1.25 +/- 0.53 nM-1 and MBC 0.59 +/- 0.14 fmol/microgram DNA (n = 3). The receptor had a sedimentation coefficient of 3.4 S, an estimated Mr of 59 kDa, and the following relative affinity for thyroid hormone analogues: TRIAC greater than L-T3 greater than L-T4. These data indicate that cultured hepatocytes and neurons of chick embryo contained T3 receptors with properties similar to those described in intact tissues from this and other species. Only the MBC of neurons was 50% lower than that observed in whole brain of embryo, but was comparable to values observed in cultured neurons from other species.
Gen Comp Endocrinol 1992 Feb
PMID:Characterization of 3,5,3'-triiodothyronine receptors in primary cultures of hepatocytes and neurons from chick embryo. 160 Dec 52

To determine whether specific hormonal responses were involved in the production of cryoprotectant (glucose) by liver of the freeze tolerant wood frog, Rana sylvatica, metabolically active hepatocytes were isolated in reasonable yields (mean 20.1 +/- 1.30% SEM, n = 29) by in situ liver perfusion with collagenase. Freshly isolated cells from autumn-collected frogs contained large amounts of glycogen (650 mumol glucosyl units/g packed cells) and produced glucose from this endogenous reserve at a rate of 10 mumol g-1 hr-1 at 0 degrees. Glucose output from cells was highly responsive to the addition of hormones; rates of glucose release increased 2.1-, 1.7-, and 1.7-fold with the addition of 10(-7) M bovine glucagon, 10(-7) M epinephrine, and 5 x 10(-6) M dibutyryl-cyclic AMP, respectively. Norepinephrine, 5-hydroxytryptamine, and bovine insulin were without effect at 0.1 microM/l. Hormone stimulation of glucose release was correlated with an increase in both the total activity and the percentage a of glycogen phosphorylase in hepatocytes. However, none of the hormones tested affected the kinetic properties of hepatocyte pyruvate kinase, suggesting the absence of covalent modification control of the enzyme. The data indicate that the freezing-stimulated production of large quantities of glucose as a cryoprotectant by R. sylvatica liver does not involve qualitative differences in the hormonal control of liver glycogenolysis, compared with other lower vertebrates. However, quantitative differences were seen, such as the much greater phosphorylase activity, 4.38 +/- 0.33 mumol min-1 g-1 packed cells, in freshly isolated R. sylvatica hepatocytes compared with 0.36 +/- 0.06 mumol min-1 g-1 in Rana pipiens hepatocytes.
Gen Comp Endocrinol 1992 Jul
PMID:Hormonal effects on glycogen metabolism in isolated hepatocytes of a freeze-tolerant frog. 162 97

Whole-cell and single channel currents were studied in cells from frog (R. pipiens and R. catesbiana) skin epithelium, isolated by collagenase and trypsin treatment, and kept in primary cultures up to three days. Whole-cell currents did not exhibit any significant time-dependent kinetics under any ionic conditions used. With an external K gluconate Ringer solution the currents showed slight inward rectification with a reversal potential near zero and an average conductance of 5 nS at reversal. Ionic substitution of the external medium showed that most of the cell conductance was due to K and that very little, if any, Na conductance was present. This confirmed that most cells originate from inner epithelial layers and contain membranes with basolateral properties. At voltages more positive than 20 mV outward currents were larger with K in the medium than with Na or N-methyl-D-glucamine. Such behavior is indicative of a multi-ion transport mechanism. Whole-cell K current was inhibited by external Ba and quinidine. Blockade by Ba was strongly voltage dependent, while that by quinidine was not. In the presence of high external Cl, a component of outward current that was inhibited by the anion channel blocker diphenylamine-2-carboxylate (DPC) appeared in 70% of the cells. This component was strongly outwardly rectifying and reversed at a potential expected for a Cl current. At the single channel level the event most frequently observed in the cell-attached configuration was a K channel with the following characteristics: inward-rectifying I-V relation with a conductance (with 112.5 mM K in the pipette) of 44 pS at the reversal potential, one open and at least two closed states, and open probability that increased with depolarization. Quinidine blocked by binding in the open state and decreasing mean open time. Several observations suggest that this channel is responsible for most of the whole-cell current observed in high external K, and for the K conductance of the basolateral membrane of the intact epithelium. On a few occasions a Cl channel was observed that activated upon excision and brief strong depolarization. The I-V relation exhibited strong outward rectification with a single channel conductance of 48 pS at 0 mV in symmetrical 112 mM Cl solutions. Kinetic analysis showed the presence of two open and at least two closed states. Open time constants and open probability increased markedly with depolarization.(ABSTRACT TRUNCATED AT 400 WORDS)
J Gen Physiol 1991 Jul
PMID:Whole-cell and single channel K+ and Cl- currents in epithelial cells of frog skin. 171 24

We previously reported that thyrotropin-releasing hormone (TRH) and human pancreatic growth hormone-releasing factor (hpGRF) exert synergistic (greater than additive) effects on growth hormone (GH) release from chicken pituitary cells in primary culture. In the present studies the possible participation of calcium in GH release and in TRH and hpGRF synergy was investigated. Following dispersion with collagenase, cells were cultured for 48 hr prior to exposure (2 hr) to test agents. Cultured cells were exposed to a range of calcium concentrations (0, 0.02, 0.2, and 2.0 mM) in the presence and absence of secretagogues. These results demonstrated that basal GH release was not altered by the concentration of calcium in the medium: however, secretagogue-induced GH release required calcium. Thus, TRH, hpGRF, 8 Br-cAMP, or forskolin stimulated GH release in the absence of calcium. Furthermore, synergistic GH release evoked by TRH and hpGRF, 8 Br-cAMP, or forskolin was observed only at the highest calcium concentration (2.0 mM). In other studies, ionomycin (10(-5) M), a calcium ionophore, stimulated GH release to a value about 125% over the basal (absence of test agent) value. Ionomycin-induced GH release was not affected by TRH (5.0 ng/ml); the combined effects of ionomycin (10(-7)-10(-5) M) and hpGRF (5.0 ng/ml) on GH release were less than additive. However, ionomycin (10(-5) M) further increased GH release over that resulting from the synergistic action of TRH and hpGRF (5.0 ng/ml each). Verapamil (a calcium channel blocker) did not affect GH release induced by either TRH or hpGRF (5.0 ng/ml each). However, this agent did inhibit synergistic GH release evoked by TRH and hpGRF, 8 Br-cAMP, forskolin, or isobutylmethylxanthine. These results suggest that calcium participates in secretagogue-induced GH release from chicken somatotrophs in vitro.
Gen Comp Endocrinol 1989 Sep
PMID:Possible participation of calcium in growth hormone release and in thyrotropin-releasing hormone and human pancreatic growth hormone-releasing factor synergy in a primary culture of chicken pituitary cells. 250 91

Currents through single potassium channels were studied in cell-attached or inside-out patches from collagenase-dispersed smooth muscle cells of the guinea pig taenia coli. Under conditions mimicking the physiological state with [K+]i = 135 mM: [K+]o = 5.4 mM, three distinct types of K+ channel were identified with conductances around 0 mV of 147, 94, and 63 pS. The activities of the 94- and 63-pS channel were observed infrequently. The 147-pS channel was most abundant. It has a reversal potential of approximately -75 mV. It is sensitive to [Ca2+]i and to membrane potential. At -30 mV, the probability of a channel being open is at a minimum. At more positive voltages, the probability follows Boltzman distribution. A 10-fold change in [Ca2+]i causes a 25-mV negative shift of the voltage where half of the channels are open; an 11.3-mV change in membrane potential produces an e-fold increase in the probability of the channel being open when P is low. At voltages between -30 and -50 mV, the open probability increases in an anomalous manner because of a large decrease of the channel closed time without much change in the channel open time. This anomalous activity may play a regulatory role in maintaining the resting potential. The histograms of channel open and closed time fit well, respectively, with single and double exponential distributions. Upon step depolarizations by 100-ms pulses, the 147-pS channel opens with a brief delay. The delay shortens and both the number of open channels and the open time increase with increasing positivity of the potential. The averaged currents during the step depolarizations closely resemble the delayed rectifying outward K+ currents in whole-cell recordings.
J Gen Physiol 1989 Nov
PMID:The Ca2+-activated K+ channel and its functional roles in smooth muscle cells of guinea pig taenia coli. 259 51

Influence of extracellular calcium on gonadotropin hormone-releasing hormone (GnRH)-stimulated gonadotropin hormone (GtH) release from a teleostean fish (Channa punctatus) pituitary was examined in vitro by preparing enzymatically dispersed pituitary cell incubation. Effect of Ca2+ on GnRH-augmented GtH release was evaluated with partially purified C. punctatus GnRH (cGnRH) and synthetic mammalian GnRH (mGnRH). Cells were dispersed by 0.3% collagenase plus 0.05% trypsin in culture medium and a high yield of viable cells were obtained. Addition of cGnRH (10 micrograms/ml) to pituitary cells in Ca2+-free medium resulted in a significant increase in GtH release, but the addition of Ca2+ (2 mM) enhanced it to about four- and threefold over cGnRH and mGnRH, respectively. Increasing concentrations of Ca2+ (0.1-2.0 mM/well) with fixed concentrations of GnRH (10 micrograms/ml) or increasing doses of GnRH (2.5 to 20 micrograms/ml) with fixed amount of Ca2+ (2 mM/well) resulted in a dose dependent increase in GtH release. EDTA or EGTA (2 mM/well) completely suppressed the Ca2+-augmenting effect of GnRH-stimulated GtH release. Addition of lanthanum (La3+, 4 mM/well), a competitive inhibitor of Ca2+, reduced 60% of the Ca2+ (2 mM/well) stimulation. Verapamil, a specific Ca2+ channel blocker, when added in increasing concentrations (1-100 microM/well) to pituitary cell incubations containing GnRH-stimulated GtH release in Ca2+-free medium could be waived by EGTA (2 mM/well), indicating availability of extracellular calcium from tissue sources. The uptake of radioactive Ca2+ by pituitary cells was greatly enhanced by GnRH while the addition of verapamil (10 microM/well) not only inhibited the GnRH-stimulated uptake, but also reduced it below the control level.(ABSTRACT TRUNCATED AT 250 WORDS)
Gen Comp Endocrinol 1989 May
PMID:Requirement of extracellular calcium in fish pituitary gonadotropin release by gonadotropin hormone-releasing hormone. 265 52

A primary culture of chicken adenohypophyseal cells has been developed to study the regulation of growth hormone (GH) secretion. Following collagenase dispersion, cells were exposed for 2 hr to vehicle (control) or test agents. Human pancreatic (tumor) growth hormone-releasing factor (hpGRF) and rat hypothalamic growth hormone-releasing factor stimulated GH release to similar levels. GH release was increased by the presence of dibutyryl cyclic AMP. Thyrotropin-releasing hormone (TRH) alone did not influence GH release; however, TRH plus hpGRF together exerted a synergistic (greater than additive) effect, increasing GH release by 100 to 300% over the sum of the values for each secretagogue acting alone. These relationships between TRH and hpGRF were further examined in cultured cells exposed to secretagogues for two consecutive 2-hr incubations. TRH pretreatment enhanced subsequent hpGRF-stimulated GH release by about 80% over that obtained if no secretagogue was present during the first incubation. In other experiments, somatostatin (SRIF) alone did not alter GH secretion. However, SRIF reduced hpGRF-stimulated GH release to levels found in controls. Furthermore, GH release stimulated by the presence of both TRH and hpGRF was lowered to control values by SRIF. The results of these studies demonstrate that a primary culture of chicken adenohypophyseal cells is a useful model for the study of GH secretion. Indeed, these results suggest that TRH and hpGRF regulate GH secretion by mechanisms which are not identical.
Gen Comp Endocrinol 1987 Mar
PMID:Growth hormone secretion from chicken adenohypophyseal cells in primary culture: effects of human pancreatic growth hormone-releasing factor, thyrotropin-releasing hormone, and somatostatin on growth hormone release. 288 41


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