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101.
Judith K. Gwathmey 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1992,162(5):401-407
Summary The subcellular mechanisms of twitch-force potentiation with paired electrical stimulation was studied in ferret ventricular myocardium using the bioluminescent calcium indicator aequorin. It is demonstrated for the first time that interpolation of an extrasystole in a train of conditioned twitches results in a beat-to-beat change in [Ca2+]i and force. Steady-state twitch force and Ca
i
2+
were increased with paired stimulation. Increased [Ca2+]0 in the setting of paired stimulation resulted in an increase in the amplitude of the postextrasystole and associated Ca2+ transient. Verapamil, a Ca2+ channel antagonist, had the opposite effect of increased [Ca2+]0. Postextrasystole potentiation was still present, but diminished in amplitude. These results indicate that postextrasystole potentiation is in part due to a verapamil-depletable store (Ca2+). Postextrasystole potentiation is therefore predominantly dependent on sarcoplasmic reticulum (SR) Ca2+ loading. Ryanodine, an alkaloid which induces Ca2+ leakage from the SR, abolished postextrasystole potentiation; however, in the presence of ryanodine the extrasystole was potentiated. Caffeine, a phosphodiesterase inhibitor which induces SR Ca2+ release and impairs uptake, also abolished postextrasystole potentiation. As with ryanodine there was resultant potentiation of the extrasystole. In the case of caffeine the calcium transient consisted of a second slow component associated with extrasystole twitch potentiation. The results are consistent with sarcolemmal Ca2+ influx playing a role in potentiation of the extrasystole in the presence of an impaired SR. These data indicate that transsarcolemmal Ca2+ influx in the presence of impaired intracellular Ca2+ buffering can directly activate the myofilaments in agreement with reports on human myocardium.Abbreviations C
conditioned stimulus
- ESI
extrasystolic interval
- Lmax
active tension
- PES
postextrasystole
- PESI
postextrasystolic interval
- SR
sarcoplasmic reticulum
- T
test stimulus 相似文献
102.
Wolfang Zeiske Heinz Marin 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1992,162(4):340-344
Summary Chloride-stimulated K+ secretion by Manduca sexta midgut (5th-instar larvae) was measured as K+-carried short-circuit current of the tissue mounted in an Ussing chamber. Microscopic parameters, such as single-channel current and channel density for the rate-determining passive transport step across the basolateral goblet cell membrane (i.e. K+ channels), were estimated by means of current-fluctuation analysis of the K+ channel blockade by haemolymph-side Ba2+ ions. Ba2+ was equally effective with Cl- or gluconate (Glu-) as the principal ambient anion. The Ba2+-induced K+ channel conduction noise is reflected by a Lorentzian, or relaxation, noise component in the power spectrum of the K+ current fluctuations. A reduced Lorentzian plateau value, but an unchanged corner frequency, were observed when Cl- was replaced by Glu-. The results from the analysis of a two-state model of K+ channel block by Ba2+, with respect to the anion-replacement effects, suggest that the observed changes in K+ current and Lorentzian plateau value mirror a complex change of the underlying parameters: Cl- omission reduces single channel current but increases channel density so that the product of single channel current and channel density is smaller in Glu- than in Cl-. It seems likely that basolateral K+ channels (1) are subject to anionic gating ligands, and (2) depend on anions with respect to the rate of K+ transfer through and open K+ channel.Abbreviations a.c.
alternating current
-
single-channel conductance
-
E
K
K+ Nernst potential
-
f
frequency contained in current noise
-
f
c
corner frequency
- Glu-
gluconate
-
G
t
transepithelial conductance
-
I
sc
short-circuit current
-
I
K
K+ current
-
I
K(max)
maximal K+ current
-
i
single-channel current
-
K
Ba
barium inhibition constant
-
K
m
Michaelis constant of saturating K+ current
-
k
01 and k
10
barium association and dissociation rate constant, respectively
-
M
K+ channel density
-
S
f
power density
-
S
o
Lorentzian plateau value
-
P
o
channel-open probability
-
P
K
K+ permeability
-
V
sc
cellular potential at short-circuit
These results have already been presented in part, at the 1989 joint meeting of the German and Israel Physiological Societies in Jerusalem (Zeiske et al. 1990). 相似文献
103.
Allan S. Schneider Hollis T. Cline Kurt Rosenheck † Martin Sonenberg 《Journal of neurochemistry》1982,37(3):567-575
Abstract: The catecholamine secretory function of a preparation of isolated bovine adrenal chromaffin cells has been further characterized under conditions designed to elucidate the mechanism of calcium channel activation and the possible role of cytoskeletal elements in stimulus-secretion coupling. Three related sets of data were obtained: (1) Differences in kinetics, Ca dependence, strength, and additivity of the secretory response to acetylcholine (ACh) versus excess K; (2) the effects on secretion of the Ca channel-blocking agents, Ni, Mg, and verapamil; and (3) the Ca dependence of vinblastine action on ACh- and K-evoked secretion. The results suggest that a major portion of the Ca influx required for catecholamine release enters the cell via voltage-dependent Ca channels with some additional Ca influx via the ACh receptor channel. Comparison of the present secretion data with corresponding known electrophysiological properties of isolated chromaffin cells provides added evidence for a role of chromaffin cell action potentials in regulation of Ca influx and the secretory response. Elevated Ca concentrations enhanced K-evoked secretion to levels comparable to that of ACh but did not induce a vinblastine block of K-evoked release. This provides further evidence against a role of microtubules in the common exocytosis event per se. However, a role of cytoskeletal elements in directing the movement of secretory granules, or an action of vinblastine at cholinergic receptors, remain distinct possibilities. 相似文献
104.
The influence of metallic, cations (added at 10 μM-1 mM) on the uptake of orthophosphate from 0.2–10 μM solution by Synechococcus leopoliensis (Racib.) Komarek was investigated. All cations tested except Mg2+ and Zn2+ stimulated phosphate uptake. The most pronounced stimulation of phosphate uptake was caused by Ca2+·Ca2+ markedly decreased the half-saturation concentration for orthophosphate uptake, apparently by acting upon the metabolic processes of phosphate transport into the cell. Phosphate did not influence Ca2+ fluxes across the cell-surface. 相似文献
105.
DOUGLAS A. EAGLES ROBERT A. GREGG DONALD M. SPOON 《The Journal of eukaryotic microbiology》1980,27(4):426-431
SYNOPSIS. The surface membrane potentials of suctorian genus Heliophrya were studied with intracellular electrodes. Resting membrane potentials averaged -32 mV, and spontaneous depolarizing potentials occurring at apparently random intervals and having a variety of waveforms were routinely observed. Such spontaneous potentials were correlated in time with visually monitored contractile vacuole activity. Individual contractile vacuoles had unique, although somewhat variable, electrical signatures. In the presence of an intracellular electrode all vacuoles contracted independently, but at approximately the same frequency. The amplitude of the electrical potentials increased when the membrane was hyperpolarized and decreased when it was depolarized. The sign of such potentials reversed at between -10 mV and the zero membrane potential. A 20% decrease in the membrane resistance was measured at the peak of the spontaneous depolarizing potentials. 相似文献
106.
Pretreatment of pigeon erythrocyte membrane vesicles with amino acids, ATP, GTP, Pi and some other simple cell constituents (singly and in combination) causes an increase in ATP-dependent Ca2+-uptake activity of vesicles upon subsequent incubation with 45Ca2+ after removal of the above agents from the ‘i’ face. Amino acids augment the stimulation by all stimulatory agents and are required for stimulation by Pi. The effects of amino acids, ATP, GTP and Pi all occur at physiological concentrations. Many if not all of the effects of the mixture of amino acids that occur naturally in the cells can be accounted for by the group transported by the ‘ASC’ transport system of Christensen (Christensen H.N. (1975) Biological Transport, 2nd edn., W.A. Benjamin, Inc., Reading, MA), but not by any single amino acid at its physiological concentration. The effects of ATP and GTP are not mimicked by their non-hydrolysable β, γ-imido analogues nor by the corresponding 3′, 5′-cyclic monophosphates. None of the effects described appears to involve calmodulin. We suggest that amino acid transport plays a role in metabolic regulation through effects on cell [Ca2+]. Analogous effects on cell [Ca2+] may be involved in the action of the many hormones which augment amino acid accumulation by the ‘A’ amino acid transport system. 相似文献
107.
108.
Allan J. Yates Sarita L. Mattison Ronald L. Whisler 《Biochemical and biophysical research communications》1980,96(1):211-218
The effect of Con-A on the incorporation of radioactivity from [14C]-glucosamine into gangliosides of human lymphocytes was investigated. Compared with non-stimulated lymphocytes there was increased incorporation into gangliosides and total lipids within the first 24 hours of exposure to Con-A. Ganglioside synthesis also occurred in later time intervals within the 96 hour incubation period. GM3 accounted for 80% of the labeled ganglioside in Con-A stimulated cells at all times studied. Thus ganglioside synthesis is not only associated with cellular division, but also occurs within a few hours of lymphocyte activation representing an extremely early prereplicative event. 相似文献
109.
Mildred S. Seelig 《Biological trace element research》1979,1(4):273-297
Except for a few experimental models of magnesium (Mg)-deficiency-induced neoplasms, less attention has been paid in the past
quarter century in the Western world to this macromineral than to the trace elements; e.g., selenium (Se) and zinc (Zn), and
to vitamins, deficiencies of which are each considered probable factors in oncogenesis. Although early epidemiologic studies
showed an inverse correlation between the amount of Mg in soil and water and the incidence of (gastric) cancer, and several
animal studies supported the premise that Mg has a prophylactic effect against induction of cancer, other studies showed that
Mg supplementation increased the growth of established experimental tumors. Thus, enthusiasm for this approach subsided. The
early epidemiologic findings have since been confirmed, and there have been studies demonstrating the importance of Mg in
maintaining immunocompetence, and others indicating that immunodeficiencies increase susceptibility to the development of
cancer. Evidence has now accrued that indicates that Mg deficiency increases susceptibility to chemical oncogens. The abnormal
metabolism of tryptophan (yielding a carcinogenic metabolite) that indicates functional or absolute pyridoxine deficiency
is an indirect clue to Mg deficiency. Vitamin B6-activated enzymes require Mg as a cofactor. However, the early warnings against the use of Mg as part of an antineoplastic
program against established cancer were justified, since rapidly metabolizing cells (such as cancers) are dependent on Mg.
There are similarities between experiences with Mg and with Se and Zn. All three are required for normal metabolism; Se also
protects against free radicals in the environment. Mg and Zn have increased established tumor growth, and their depletion
has been applied to antineoplastic programs, with risks comparable to those of using antimetabolic agents. 相似文献
110.
D. L. Fine L. O. Arthur L. J. T. Young 《In vitro cellular & developmental biology. Plant》1976,12(10):693-701
Summary Several cell culture factors were found to influence in vitro expression of mouse mammary tumor virus (MMTV) in the mouse
adenocarcinoma cell line Mm5mt/c1. Cells were propagated in a variety of commercially available cell culture media to which dexamethasone (DXM) was added as
a stimulator of MMTV production. Culture seeding density, culture medium type, and glucose concentration each influenced MMTV
production when expressed on a per cell basis. Maximum cell growth occurred in cultures grown in RPMI-1640 medium containing
insulin. Those media which provided good cell growth were not necessarily optimal for virus expression. Addition of insulin
did not stimulate MMTV synthesis although dexamethasone alone was stimulatory in all media used; however, maximum MMTV expression
was obtained when dexamethasone and insulin were used in concert. Equivalent levels of MMTV-specific cell membrane antigen,
MMTV-specific protein, and virus particles were produced at incubation temperatures of 32°, 34° or 37° C; however, higher
levels of virus-related RNA-dependent DNA polymerase (RDDP) activity were recovered from cultures incubated at 32° and 34°
C than at 37° C. Decreased levels of RDDP were attributed to enzyme thermolability at 37° C incubation.
Research sponsored by the National Cancer Institute under Contract No. N01-CO-25423 with Litton Bionetics, Inc., and Contract
No. N01-CP-33253 with the University of California. 相似文献