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  • 1
    Electronic Resource
    Electronic Resource
    Calcium transients which accompany the activation of sodium current in rat ventricular myocytes at 37°C: a trigger role for reverse Na-Ca exchange activated by membrane potential? (1995)
    Springer
    Pflügers Archiv 430 (1995), S. 887-893 
    Details
    ISSN: 1432-2013
    Keywords: Sodium current ; Na-Ca exchange ; Excitation-contraction coupling ; Cardiac myocyte ; Calcium transient
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We investigated the role of the fast sodium current (I Na) in triggering Ca release from the sarcoplasmic reticulum (SR), using adult rat left ventricular myocytes, loaded with Fura-2 to measure intracellular Ca (Cai), which were whole-cell patch-clamped at 35–37°C. Before each test pulse, a series of 400-ms conditioning pulses to +10 mV were applied to establish a constant level of SR Ca load. Pulses were applied every 15 s. A test pulse from −80 mV to −50 mV elicited a rapidI Na and a phasic Cai transient. When the solution perfusing a myocyte was rapidly switched for 15 s before a test pulse to one containing the L-type Ca channel blocker nifedipine (20 μM), the test pulse still activatedI Na and a phasic Cai transient, the amplitude of which was not significantly different from control (P〉0.05;t-test). When a rapid switch to 20 μM nifedipine plus 30 μM tetrodotoxin (TTX) was made 15 s before a test pulse, bothI Na and the Cai transient were completely abolished (n=6). When a switch was made to Na-free (Li) solution, which contained 20 μM nifedipine to block L-type Ca current,I Ca,L, there was no significant difference in the Cai transient amplitude from that of control (P〉0.05;n=6). Brief depolarising test pulses (−80 mV to +20 mV, 10 ms duration) to simulate membrane potential escape also elicited a Cai transient which attained 90.0% (±2.8%;n=7) of the Cai transient activated by a conditioning pulse to +10 mV. The Cai transient with a brief pulse was not significantly affected by application of 20 μM nifedipine (P〉0.05), but adding TTX with nifedipine reduced the Cai transient amplitude to 76.9% (±6.8%;P〈0.02;n=8). In four cells, the Cai transient remaining in the presence of nifedipine plus TTX was abolished by adding 5 mM Ni. These data are consistent with “voltage escape” during activation ofI Na leading to a trigger Ca entry via a mechanism other than L-type Ca channels or subsarcolemmal Na accumulation with reverse Na-Ca exchange. The block by Ni of the Cai transient suggests that a brief membrane potential escape might directly activate reverse mode Na-Ca exchange to trigger SR release, and this mechanism would seem to account largely for the Cai transient which accompaniesI Na in rat myocytes, under these experimental recording conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01837401
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  • 2
    Electronic Resource
    Electronic Resource
    The Fura-2 transient can show two types of voltage dependence at 36°C in ventricular myocytes isolated from the rat heart (1996)
    Springer
    Pflügers Archiv 432 (1996), S. 215-224 
    Details
    ISSN: 1432-2013
    Keywords: Key words Excitation-contraction coupling ; Na-Ca exchange ; Calcium transient ; cardiac myocyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We used the whole-cell patch-clamp method to investigate the voltage dependence of the L-type Ca current (I Ca,L) and intracellular Ca (Cai) transient in ventricular myocytes isolated from the rat heart. Intracellular Ca was monitored using Fura-2 and the experiments were carried out at 36° C. We measured I Ca,L by using a caesium-based internal dialysis solution to eliminate interfering K currents. The voltage dependence of peak I Ca,L amplitude was bell-shaped: I Ca,L was maximal at +10 mV and declined at more positive potentials. When I Ca,L was integrated over the first 25 ms to estimate the magnitude of Ca entry, this had a very similar voltage dependence to peak I Ca,L. In all cells, phasic Fura-2 transients were abolished by 5 μM ryanodine (a blocker of the sarcoplasmic reticulum, SR) showing that the Fura-2 transient provided an index of the magnitude of SR Ca release. For experiments measuring the Cai transient, we used a K-based internal dialysis solution to preserve normal excitation-contraction coupling. In 30–40% of cells, we found that the Fura-2 transient had a bell-shaped voltage dependence. This suggests that, in these cells, the primary trigger mechanism for Ca-induced Ca-release might have been Ca entry via I Ca,L. In the remaining 60–70% of cells, the voltage dependence of the Fura-2 transient was not bell-shaped. The Fura-2 transient reached a maximum with a pulse to +10 mV, and the amplitude of the transient did not decline significantly at more positive potentials to this. In cells with a non-bell-shaped voltage dependence of the Fura-2 transient, pulses to potentials as far positive as +140 mV elicited phasic Fura-2 transients. Since this potential exceeded the Nernst potential for Ca, it was unlikely there was any tigger Ca entry via I Ca,L at this potential. This would suggest that, in these cells, another trigger for SR Ca release (in addition to I Ca,L) might be present. We conclude that rat ventricular myocytes, produced using a standard isolation technique and under standard recording conditions, can show either a bell-shaped or a sigmoidal voltage dependence of the Fura-2 transient.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050127
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  • 3
    Electronic Resource
    Electronic Resource
    Voltage dependence of the Fura-2 transient in rabbit left atrial myocytes at 37°C (1997)
    Springer
    Pflügers Archiv 433 (1997), S. 817-826 
    Details
    ISSN: 1432-2013
    Keywords: Key words Excitation ; contraction coupling ; Na-Ca exchange ; Calcium transient ; Atrial myocyte ; Cardiac myocyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  We used the whole-cell patch-clamp technique and monitoring of Fura-2 fluorescence to investigate the voltage dependence of the L-type Ca current (I Ca,L) and intracellular Ca (Cai) transient in rabbit atrial myocytes at 37°C. Imaging the atrial cell membrane with Di-4-ANNEPS showed (in contrast to ventricular cells) that atrial cells had very few transverse tubules. We measured I Ca,L using a Cs-based internal dialysis solution to eliminate interfering K currents. The voltage dependence of peak I Ca,L amplitude was bell-shaped: I Ca,L was maximal at +10 mV and declined at more negative and positive potentials. For measuring the Fura-2 (Cai) transient, we used a K-based internal dialysis solution to preserve normal excitation–contraction coupling. Ryanodine (20 μM) plus thapsigargin (2 μM) (blockers of the sarcoplasmic reticulum, SR) abolished the phasic component of the Fura-2 transient (n = 5), demonstrating that the phasic Fura-2 transient provided an index of the magnitude of SR release. The Fura-2 transient also showed bell-shaped voltage dependence, but this was different from that for I Ca,L. The Fura-2 transient peaked at +30 mV and partially declined at more positive potentials; but at potentials where inward I Ca,L was small (if not absent), the phasic Fura-2 transient still attained a significant amplitude. We used a rapid application of nifedipine (32 μM), and of nifedipine plus 5 mM Ni, to assess the ability of I Ca,L and reverse-mode Na-Ca exchange to trigger SR Ca release. With test pulses to +10 mV and +60 mV, a rapid switch to nifedipine (which blocked I Ca,L) produced no significant reduction in phasic Fura-2 transient amplitude. This suggests that in the absence of I Ca,L, another mechanism was able to trigger SR release. With pulses to +10 and +60 mV, a single beat switch to nifedipine plus 5 mM Ni almost completely abolished the phasic transient. Since 5 mM Ni inhibits Na-Ca exchange, this suggests that, in the absence of I Ca,L, trigger Ca entry via reverse Na-Ca exchange was able to activate SR Ca release in atrial cells at 37°C. The mechanisms underlying the Fura-2 transient in atrial cells, and differences with pre-existing data from rabbit ventricular cells, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050350
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  • 4
    Electronic Resource
    Electronic Resource
    Invertebrate drift in the Dan River, Israel (1988)
    Springer
    Hydrobiologia 160 (1988), S. 155-163 
    Details
    ISSN: 1573-5117
    Keywords: invertebrate drift ; aquatic insects ; river ecology ; Gammarus ; Baetidae ; environmental impact ; Israel ; Jordan River
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Dan river, a principal source of the Jordan River, Israel, is unusually constant in discharge (∼8 m3·s−1) and water temperature (15–16 °C). The Jordan headwaters constitute the southernmost oasis of a palearctic north temperate fauna, and presumably the very constancy of the Dan contributes to its important role as a regional refuge. However, little is known of river ecology from this region. We report a twelve month study of drift, undertaken to assess diel, seasonal, and spatial patterns of the abundance of drifting invertebrates. Diel periodicity in drift was detectable but minimal. Baetidae nymphs showed a pronounced nocturnal increase, gammarid amphipods a modest, twofold increase, while dipteran larvae showed no diel variation. Seasonal variation likewise was minimal and due principally to the Baetidae, while gammarid amphipods showed no significant seasonality. The notably small diel and seasonal variation in aquatic drift in the Dan may be attributable to the extremely constant physical regime. Spatial variation was substantial. Two stations located 30 and 200 m below the karstic exsurgence of the Dan provided drift densities among the lowest reported anywhere, whereas two stations located 1 and 4.5 km downstream had more typical drift densities. A water diversion project completed halfway through the study resulted in a 50% reduction in flow at the most downstream stations, but had no discernible effect on drift.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00015478
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  • 5
    Electronic Resource
    Electronic Resource
    Diel activity of Gammarus pulex (Crustacea) in a South Swedish stream: comparison of drift catches vs baited traps (1989)
    Springer
    Hydrobiologia 179 (1989), S. 73-80 
    Details
    ISSN: 1573-5117
    Keywords: invertebrate drift ; chemical attractants ; fish predation ; river ecology ; Sweden ; Gammarus ; Limnephilidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We examined the relationship between drift and foraging activity in Gammarus pulex L. by comparing collections from the benthos, drift, and small traps baited with cheese. Two sites were employed, one with both sculpins and trout, and one lacking fish. Baited traps collected large numbers of G. pulex within as little as 15 min, demonstrating the effectiveness of chemical attractants. Limnephilid larvae also were attracted rapidly, and no counteracting influence on either taxon could be detected to result from a sculpin in an adjacent cage. Trap collections indicate a highly aggregated distribution and suggest that one use of this approach is for detecting small scale spatial patterns. Individuals of small size comprised the majority of the G. pulex population. Of three size categories used ( 〈 4, 4–8, 〉 8 mm total length), between 63 and 67% of the benthic collections were 〈 4 mm long. Traps captured exclusively the two largest size classes of G. pulex. Drift collections consisted almost exclusively (93–100%) of 〈 4 mm individuals during the day, and larger G. pulex appeared only in the night drift. Based on stomach analysis, trout and sculpins selectively captured larger prey but this preference was proportional to fish size, as small sculpins captured relatively smaller prey. The rarity of larger G. pulex in the daytime drift appears to be attributable to greater risk of predation by day, but not to the absence of foraging activity in the amphipod, as baited traps and direct observation indicated that G. pulex is continuously active.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00011931
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