The initiation of excitation and light adaptation in Limulus ventral photoreceptors.

Lisman, John; Strong, Judith A.

doi:10.1085/jgp.73.2.219

Cited by 59 publications

(35 citation statements)

References 35 publications

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“…Dim background intensities slightly desensitize the cell; with higher intensities, the log desensitization is linearly related to the log background intensity. The slope (n) of the linear portion for five cells is given in Table IV; it had an average of 0.76 ± 0 .10 (SD), which is similar to the slopes measured by Lisman and Strong (1979) (see also Wong, 1978). The intersection between the linear portion of the incremental threshold curve and the horizontal portion where desensitization is zero can be defined as the threshold of adaptation (dashed lines on Fig.…”

Section: Resting Ca Isupporting

confidence: 63%

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Relationship between light sensitivity and intracellular free Ca concentration in Limulus ventral photoreceptors. A quantitative study using Ca-selective microelectrodes.

Levy¹,

Fein²

1985

The Journal of General Physiology

101

106

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The possible role of Ca ions in mediating the drop insensitivity associated with light adaptation in Limulus ventral photoreceptors was assessed by simultaneously measuring the sensitivity to light and the intracellular free Ca concentration (Ca i) ; the latter was measured by using Ca-selective microelectrodes . In dark-adapted photoreceptors, the mean resting Cai was 3 .5 ± 2 .5,M SD (n = 31) . No correlation was found between resting Cai and absolute sensitivity from cell to cell . Typically, photoreceptors are not uniformly sensitive to light ; the Cai rise evoked by uniform illumination was 20-40 times larger and faster in the most sensitive region of the cell (the rhabdomeral lobe) than it was away from it . In response to a brief flash, the Cai rise was barely detectable when 10 2 photons were absorbed, and it was saturated when^-10 5 photons were absorbed . During maintained illumination, starting near the threshold of light adaptation, steady Cai increases were associated with steady desensitizations over several log units of light intensity : a 100-fold desensitization was associated with a 2 .5-fold increase in Ca ; . After a bright flash, sensitivity and Cai recovered with different time courses : the cell was still desensitized by -0 .5 log units when Ca i had already recovered to the prestimulus level, which suggests that under those conditions Cai is not the rate-limiting step of dark adaptation . Ionophoretic injection of EGTA markedly decreased the light-induced Cai rise and increased the time to peak of the light response, but did not alter the resting Ca;, which suggests that the time to peak is affected by a change in the capacity to bind Ca2' and not by resting Ca i . Lowering the extracellular Ca 21 concentration (Ca .) first decreased Cai and increased sensitivity. Longer exposure to low Ca. resulted in a further decrease of Ca ; but decreased rather than increased Address reprint requests to Dr.

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Section: Resting Ca Isupporting

confidence: 63%

“…Light adaptation can easily be quantified over a broad range of light intensities using the increment-threshold curve (see, e.g., Lisman and Strong, 1979). Therefore, simultaneous measurements of incremental light responses Ca signals were made for increasing intensities of steady background illumination .…”

Section: Resting Ca Imentioning

confidence: 99%

Relationship between light sensitivity and intracellular free Ca concentration in Limulus ventral photoreceptors. A quantitative study using Ca-selective microelectrodes.

Levy¹,

Fein²

1985

The Journal of General Physiology

101

106

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“…For the determination of 13, fibers were first equilibrated for 58-84 min with the K-glutamate solution with 20 mM EGTA plus 1.76 mM Ca and 0.63 mM phenol red (no fura-2) in the end pools; Ringer's solution was used in the central pool. (Lisman and Strong, 1979), the AA(420) signal is expected to be of opposite sign, as observed.…”

Section: A Description Of the Methods For The Determination Of The Rapsupporting

confidence: 54%

“…For this purpose, the value of the molar extinction coefficient of phenol red at 480 nm, e(480), was taken to be 1.1 • 104 M-acm -1 (Lisman and Strong, 1979). For protonated and nonprotonated indicator, a small correction was applied to the value of 8(480) to allow for the slight difference between the wavelength of light passed by the 480-nm filter and the exact isosbestic wavelength of phenol red in a calibration solution.…”

Section: Estimation Of Myoplasmic Ph With Phenol Redmentioning

confidence: 99%

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Calcium release and its voltage dependence in frog cut muscle fibers equilibrated with 20 mM EGTA.

Pape

Jong

Chandler

1995

The Journal of General Physiology

129

295

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Sarcoplasmic reticulum (SR) Ca release was studied at 13-16~ in cut fibers (sarcomere length, 3.4-3.9 I~m) mounted in a double Vaseline-gap chamber. The amplitude and duration of the action-potential stimulated free [Ca] transient were reduced by equilibration with end-pool solutions that contained 20 mM EGTA with 1.76 mM Ca and 0.63 mM phenol red, a maneuver that appeared to markedly reduce the amount of Ca complexed by troponin. A theoretical analysis shows that, under these conditions, the increase in myoplasmic free [Ca] is expected to be restricted to within a few hundred nanometers of the SR Ca release sites and to have a time course that essentially matches that of release. Furthermore, almost all of the Ca that is released from the SR is expected to be rapidly bound by EGTA and exchanged for protons with a 1:2 stoichiometry. Consequently, the time course of SR Ca release can be estimated by scaling the ApH signal measured with phenol red by -13/2. The value of 13, the buffering power of myoplasm, was determined in fibers equilibrated with a combination of EGTA, phenol red, and fura-2; its mean value was 22 mM/pH unit. The Ca content of the SR (expressed as myoplasmic concentration) was estimated from the total amount of Ca released by either a train of action potentials or a depleting voltage step; its mean value was 2,685 I~M in the action-potential experiments and 2,544 IxM in the voltage-clamp experiments. An action potential released, on average, 0.14 of the SR Ca content with a peak rate of release of,'~5 %/ms. A second action potential, elicited 20 ms later, released only 0.6 times as much Ca (expressed as a fraction of the SR content), probably because Ca inactivation of Ca release was produced by the first action potential. During a depolarizing voltage step to 60 mV, the rate of Ca release rapidly increased to a peak value of~3 %/ms and then decreased to a quasi-steady level that was only 0.6 times as large; this decrease was also probably due to Ca inactivation of Ca release. SR Ca release was studied with small step depolarizations that open no more than one SR Ca channel in 7

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Protein kinase C‐induced disorganization and endocytosis of photosensitive membrane in Limulus ventral photoreceptors

Dabdoub

Payne

Jinks

2001

J of Comparative Neurology

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Protein kinase C (PKC) desensitizes the light response in photoreceptors from the ventral optic nerve of the horseshoe crab Limulus. Photoisomerization of Limulus rhodopsin leads to phosphoinositide hydrolysis, resulting in the production of inositol trisphosphate and diacylglycerol (DAG). Inositol trisphosphate mobilizes intracellular stores of Ca(2+), resulting in photoreceptor excitation in Limulus, while DAG may activate PKC. We investigated whether PKC-mediated desensitization of the photoresponse is accompanied by ultrastructural changes in the rhodopsin-bearing photosensitive membrane (rhabdom) in Limulus ventral photoreceptors. PKC activation by (-)-indolactam V in darkness induces disorganization and swelling of the rhodopsin-containing microvilli and endocytosis of rhabdomeral membrane. The effects of (-)-indolactam V on dark-adapted photoreceptor ultrastructure are reversible, are stereospecific, are blocked by coapplication of PKC inhibitors, and closely match those induced by continuous, bright light. Rhabdom disorganization and endocytosis via PKC activation may, therefore, contribute to desensitization of the light-adapted photoreceptor.

show abstract

The initiation of excitation and light adaptation in Limulus ventral photoreceptors.

Cited by 59 publications

References 35 publications

Relationship between light sensitivity and intracellular free Ca concentration in Limulus ventral photoreceptors. A quantitative study using Ca-selective microelectrodes.

Relationship between light sensitivity and intracellular free Ca concentration in Limulus ventral photoreceptors. A quantitative study using Ca-selective microelectrodes.

Calcium release and its voltage dependence in frog cut muscle fibers equilibrated with 20 mM EGTA.

Protein kinase C‐induced disorganization and endocytosis of photosensitive membrane in Limulus ventral photoreceptors

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