Potassium conductance and internal calcium accumulation in a molluscan neurone

Gorman, A. L. F.; Thomas, Mandy

doi:10.1113/jphysiol.1980.sp013472

Cited by 170 publications

(140 citation statements)

References 35 publications

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“…Fig. 1 A shows the outward current that is activated by ionophoretic injection of Ca into this cell, and the result is qualitatively similar to that observed in molluscan neurones (Gorman & Thomas, 1980). The reversal potential varies with the external K concentration in a manner which is again similar to that seen in molluscan neurones (Meech, 1972), approaching a Nernstian response for [K] > 30 mm (Fig.…”

Section: Psupporting

confidence: 65%

Communications

1981

The Journal of Physiology

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Section: Psupporting

confidence: 65%

Communications

1981

The Journal of Physiology

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“…Thus, even though the membrane clearly depolarizes (Fig. 1A) (61,62). The presence of vacuoles in fungal and plant cells, but not in animal cells, suggests that this organelle might provide the major intracellular source of very effective Ca2+ buffering in Neurospora.…”

Section: Methodsmentioning

confidence: 99%

Cytosolic calcium homeostasis in fungi: roles of plasma membrane transport and intracellular sequestration of calcium.

Miller

Vogg

Sanders

1990

Proc. Natl. Acad. Sci. U.S.A.

100

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Cytosolic free calcium ([Ca2+]k) has been measured in the mycelial fungus Neurospora crassa with Ca2+-selective microelectrodes. The mean value of [Ca2+J is 92 ± 15 nM and it is insensitive to external pH values between 5.8 and 8.4. Simultaneous measurement of membrane potential enables the electrochemical potential difference for Ca2+ across the plasma membrane to be estimated as about -60 kJimol'-a value that cannot be sustained either by a simple Ca2+-ATPase, or, in alkaline conditions, by straightforward H+/Ca2+ exchange with a stoichiometric ratio of <5 H+/Ca2+. We propose that the most likely alternative mechanism of Ca2+ efflux is ATP-driven H+/Ca2+ exchange, with a stoichiometric ratio of at least 2 H+/Ca2 . In accord with this proposal, depletion of the ATP level from 2.5 to 0.5 mM by CN-elicits an increase in [Ca2+Jc, but only in alkaline conditions in which the putative H+/Ca2+-ATPase would be selectively stalled. The insensitivity of Ca2+ homeostasis to CN-in more acid conditions implies that the Km (ATP) of the transport system is 100 ,uM or less. The increase in [Ca2+1C in the presence of CN-at pH 8.4 (50 nM-min-') is compared with 45Ca2+ influx (0.62 mMniinif') under the same conditions. The proportion of entering Ca2+ remaining free in the cytosol is only 8 X 10-5, and since the concentration of available chelation sites on Ca2+-binding proteins is unlikely to exceed 100 ,uM, a major role for the fungal vacuole in short-term Ca2+ homeostasis is indicated. This notion is supported by the observation that cytosolic Ca2+ homeostasis is disrupted by a protonophore, which rapidly abolishes tbe driving force (a transmembrane pH difference) for Ca2+ uptake into fungal vacuoles.Cytosolic free calcium ([Ca2+]

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“…cells, the largest peak phase II tail current occurred at pulse potentials between +20 and + 40 mV, and the amplitude of the current elicited by a pulse to + 100 mV ranged from 10 to 20 % of the largest current. Various neurophysiological processes which require Ca2+ influx also display an inverted U-shaped relationship with pulse potential; for example, the activation of IK(Ca) (Meech & Standen, 1975;Gorman & Thomas, 1980a), Ca2+-dependent inactivation of Ca2+ current (Brehm & Eckert, 1978;Eckert & Tillotson, 1981); and neurotransmitter release at squid central synapses (Katz & Miledi, 1967). Therefore, it seems likely that the inward current which predominates during phase II is Ca2+-activated.…”

Section: Slow Tail Currents In Bursting Neuronesmentioning

confidence: 99%

Calcium‐dependent inward current in Aplysia bursting pace‐maker neurones.

Krämer¹,

Zucker²

1985

The Journal of Physiology

124

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SUMMARY1. Depolarizing voltage-clamp pulses elicit a triphasic series of tail currents (phase I, II and III) in Aplysia burst-firing neurones L2-L6. The sequence and time course of the tail currents resemble slow changes in membrane potential which follow bursts in the unclamped cell.2. The phase II tail current is an inward current with a time course similar to that of the depolarizing after-potential (d.a.p.) which follows bursts in the unclamped cell.The phase II tail current is suppressed by depolarizing pulses which approach Eca, is blocked by Ca2+ current antagonists (Co2+ and Mn2+), and is blocked by intracellular injection of EGTA.3. The phase II tail current is not blocked by agents which block Na+-dependent action potentials, the Na+{-Ca2+ exchange pump, or the Na+-K+ exchange pump. The phase II tail current is not blocked by the elimination of large outward K+ currents which can lead to extracellular K+ accumulation. Thus, the phase II tail current is not generated by any of these processes.4. The phase II tail current is reduced by about 60 % following substitution of tetramethylammonium (TMA+) for external Na+, but is unaffected by reducing external Cl-.5. The phase II tail current is distinct from a persistent inward Ca2+ current which underlies the negative resistance region of the steady-state current-voltage relation of bursting cells. The persistent inward current is only slightly reduced by TMA+ substitution for Na+, and is enhanced by EGTA injection.6. Injection of Ca2+ into Aplysia bursting cells elicits a biphasic (inward-outward)current. The inward current can be observed in isolation after blocking the outward component (Ca2+-activated K+ current) with 50 mM-external tetraethylammonium. 7. The Ca2+-elicited inward current has a reversal potential near -22 mV, and is non-selective for Na+, K+ and Ca2+. The reversal potential is unaffected by changes in Cl-and pH. The Ca2+-activated conductance is apparently voltage independent.8. We propose that the phase II tail current, and hence the d.a.p., is due to the Ca2+-dependent activation of a voltage-independent non-specific cationic conductance. This conductance participates in generating the depolarizing phase of bursting pace-maker activity.

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Potassium conductance and internal calcium accumulation in a molluscan neurone

Cited by 170 publications

References 35 publications

Communications

Communications

Cytosolic calcium homeostasis in fungi: roles of plasma membrane transport and intracellular sequestration of calcium.

Calcium‐dependent inward current in Aplysia bursting pace‐maker neurones.

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