Selective inhibition of the phospholipase C pathway blocks one light-activated current component in Limulus photoreceptor

Contzen, Klaus; Richter, Klaus; Nagy, K.

doi:10.1007/bf00207189

Cited by 14 publications

(6 citation statements)

References 38 publications

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“…These data agree with the broadly accepted view that invertebrate photocurrents are activated via the PLC pathway, as has been reported for other invertebrates, such as Limulus~Nagy &Contzen, 1997! andDrosophila~Hardie &Raghu, 1998!, and that the InsP 3 pathway can also play a significant role in transduction, again as has been demonstrated in other photoreceptor cells~Frank Contzen et al, 1995;Ukhanov & Walz, 2001!. The role of IP 3 was also investigated using another IP 3 receptor inhibitor, 2-amino-ethoxydiphenylborate~2-APB!…”

Section: Signal Pathwaymentioning

confidence: 89%

Whole-cell recording of light-evoked photoreceptor responses in a slice preparation of the cuttlefish retina

2005

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A new tissue slice preparation of the cuttlefish eye is described that permits patch-clamp recordings to be acquired from intact photoreceptors during stimulation of the retina with controlled light flashes. Whole-cell recordings using this preparation, from the retinas of very young Sepia officinalis demonstrated that the magnitude, latency, and kinetics of the flash-induced photocurrent are closely dependent on the magnitude of the flash intensity. Depolarizing steps to voltages more positive than -40 mV, from a membrane holding potential of -60 mV, induced a transient inward current followed by a larger, more sustained outward current in these early-stage photoreceptors. The latter current resembled the delayed rectifier (I(K)) already identified in many other nerve cells, including photoreceptors. This current was activated at -30 mV from a holding potential of -60 mV, had a sustained time course, and was blocked in a dose-dependent manner by tetraethylammonium chloride (TEA). The smaller, transient, inward current appeared at potentials more positive than -50 mV, reached peak amplitude at -30 mV and decreased with further depolarization. This current was characterized as the sodium current (I(Na)) on the basis that it was inactivated at holding potentials above -40 mV, was blocked by tetrodotoxin (TTX) and was insensitive to cobalt. Intracellular perfusion of the photoreceptors, via the patch pipette, demonstrated that U-73122 and heparin blocked the evoked photocurrent in a dose-dependent manner, suggesting the involvement of the phospholipase C (PLC) and inositol 1,4,5-triphosphate (InsP(3)), respectively, in the phototransduction cascade. Perfusion with cyclic GMP increased significantly the evoked photocurrent, while the inclusion of phorbol-12,13-dibutyrate reduced significantly the evoked photocurrent, supporting the involvement of cGMP and the diacylglycerol (DAG) pathways, respectively, in the cuttlefish transduction process.

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Section: Signal Pathwaymentioning

confidence: 89%

Whole-cell recording of light-evoked photoreceptor responses in a slice preparation of the cuttlefish retina

2005

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“…Intra cellular application of the calcium chelator BAPTA completely blocked the C2 component in the photocurrent, while the other components were only moderately influenced. The C2 compo nent is thought to include the InsP3-induced calcium release from the internal stores (Contzen et al, 1995). Similarly, only one type of bumps in the ventral photoreceptor, the "standard" or C2 bumps that constitute the macroscopic C2 compo nent (Nagy, Contzen and Stieve, 1993), are influ enced by changes in Ca^ The Q bumps with smaller amplitudes and slower kinetics are virtu ally insensitive.…”

Section: Depleting the Internal Calcium Storesmentioning

confidence: 99%

“…Injection of M. D orlöchter et al ■ Calcium -Independent Photoresponse in Lim ulus Ventral Photoreceptor 447 calcium into ventral photoreceptors increased the light response in calcium-deprived cells, or elicited inward currents similar to those caused by light so that an obligatory role for calcium in excitation was proposed (Bolsover and Brown, 1985;Payne, Corson and Fein, 1986b;Shin, Richard and Lisman, 1993). On the other hand, application of calcium buffer or agents blocking calcium release did not completely inhibit the photocurrent indi cating calcium-independent initiation of a light re sponse (Frank and Fein, 1991;Contzen, Richter and Nagy, 1995).…”

Section: Introductionmentioning

confidence: 99%

Effects of Calcium and Cyclopiazonic Acid on the Photoresponse in the Limulus Ventral Photoreceptor

Dorlöchter

Yuan

Stieve

1999

Zeitschrift Für Naturforschung C

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Phototransduction, Current Components, Light Adaptation, Bumps, CPA 1. Single-photon responses (bumps) and small macroscopic photocurrents were studied in ventral photoreceptors of the horseshoe crab Limulus. Lowering the calcium concentration in the bath from 10 mM to 250 fiM led to increased bump size. Adaptation of the cells by a moderately bright conditioning flash was not impaired.2. Pressure-injection of 1.2 mM EG TA into the dark-adapted cells resulted in reduced bump size. EG TA weakened the effect of the conditioning light flash although it did not completely abolish light adaptation.3. The microsomal calcium-ATPase inhibitor cyclopiazonic acid strongly desensitized the cells, and bumps were suppressed below detection. When the bathing saline contained 10 m M calcium, macroscopic photoresponses after extracellular application of the agent had ampli tudes smaller than under control conditions but normal response kinetics: The response to a light step still consisted of a fast transient photocurrent and a much smaller plateau. How ever, when applied in calcium-free bathing saline, cyclopiazonic acid additionally influenced the waveform of the photoresponse. The clear distinction between transient and plateau was no longer possible, and the photocurrent appeared "square".4. Our results support the idea that a transient elevation of the cytosolic calcium concentra tion is obligatory for light adaptation in the ventral photoreceptor. It is also obligatory for the generation of the so-called C2 component of the photocurrent which is represented by "standard" bumps and the fast transient phase of a prolonged response. However, a rise in cytosolic calcium appears not necessary for the initiation of a slow electrical photoresponse.

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“…These authors propose that cytosolic Ca 2ϩ is required for the initial processes of excitation, and that the efficiency of excitation increases as Ca 2ϩ is released from the intracellular stores in the submicrovillar cisternae. Blocking this increase in Ca i by injection of calcium buffers containing either BAPTA (Contzen et al, 1995) or dibromoBAPTA (Shin et al, 1993) attenuated the light response without causing the plateaus.…”

Section: Discussionmentioning

confidence: 99%

“…The intracellular injection of IP 3 or Ca 2ϩ induces membrane currents with properties similar to those activated by light Fein et al, 1984;Payne et al, 1986a,b), and the times required for activation of the light-dependent currents and elevation of Ca i are the same (Ukhanov & Payne, 1997). Maintenance of low Ca i by the injection of the calcium chelator 5,59-dibromo-BAPTA reduces these currents (Shin et al, 1993), and specific portions of the currents are blocked by the injection of neomycin or spermine (Faddis & Brown, 1993;Contzen et al, 1995), which inhibit phospholipase C (PLC). In excised patches of Limulus photoreceptor membrane, these channels are activated by cyclic GMP, and not IP 3 or Ca 2ϩ (Bacigalupo et al, 1991).…”

Section: Introductionmentioning

confidence: 99%

Inhibition of the calcineurin-like protein phosphatase activity in Limulus ventral eye photoreceptor cells alters the characteristics of the spontaneous quantal bumps and the light-mediated inward currents, and enhances arrestin phosphorylation

et al. 1998

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Changes in intracellular calcium are involved in phototransduction processes in both vertebrate and invertebrate photoreceptors. During this phototransduction process in the Limulus ventral eye, there is a biochemical change in the protein phosphatase, calcineurin, such that it becomes capable of activation by calcium and calmodulin. Here we show that the calcium/calmodulin-dependent calcineurin-like activity in light-adapted ventral eye was completely inhibited by the CaN autoinhibitory peptide, CaN A457-482 and the Merck analog of the membrane-permeable, immunosuppressant drug, FK 506, L-683, 590, but not an inactive analogue, L-685, 818. Whole-cell, voltage-clamp recordings of spontaneous quantal bump activity present in dark-adapted photoreceptors injected with either CaN A457-482 (500 microM) or superfused with L-683, 590 (20 microM) or L-685, 818 revealed that both CaN A457-482 and L-683, 590, but not L-685, 818, caused rapid decreases in quantal bump amplitude, rise time and fall time, resulting in smaller, sharper bumps. This was correlated with enhanced phosphorylation of arrestin in light-adapted ventral eye photoreceptors exposed to L-683, 590 or less reliably okadaic acid. Both CaN A457-482 and L-683, 590 markedly affected the light-stimulated inward currents recorded from light-adapted ventral photoreceptors, causing a "terracing" of the inward current, and an intensity-dependent delay in the time required to reach peak amplitude. Consequently, inhibition of calcineurin markedly affects two major rhodopsin-dependent electrophysiological processes, and implicates CaN as an integral component in the phototransduction cascade.

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Selective inhibition of the phospholipase C pathway blocks one light-activated current component in Limulus photoreceptor

Cited by 14 publications

References 38 publications

Whole-cell recording of light-evoked photoreceptor responses in a slice preparation of the cuttlefish retina

Whole-cell recording of light-evoked photoreceptor responses in a slice preparation of the cuttlefish retina

Effects of Calcium and Cyclopiazonic Acid on the Photoresponse in the Limulus Ventral Photoreceptor

Inhibition of the calcineurin-like protein phosphatase activity in Limulus ventral eye photoreceptor cells alters the characteristics of the spontaneous quantal bumps and the light-mediated inward currents, and enhances arrestin phosphorylation

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