Ca(2+)-dependent and Ca2+ release-dependent excitation in leech photoreceptors: evidence from a novel "inside-out" cell model

Cell Calcium
B WalzK Ukhanov

Abstract

We have developed a novel, electrophysiologically intact and light-sensitive "inside-out" cell model (IOCM) of microvillar photoreceptors of the leech Hirudo medicinalis. Light responses recorded from the IOCM with sharp microelectrodes are depolarizations with amplitudes of up to 50-60 mV. In darkness, graded elevations of the free Ca(2+) concentration in the "intracellular medium" (ICM) reversibly increase the conductance of the microvillar membrane leading to Ca(2+)-induced graded voltage changes up to approximately 50 mV. The threshold for Ca(2+)-induced voltage changes is approximately 0.06 microM, EC(50) is approximately 1.2 microM, and saturation occurs at approximately 20 microM free Ca(2+). Small Ca(2+) elevations (<0.6 microM) produce discrete waves of depolarization resembling quantum bumps. Stimulating IOCMs with short (20-ms) and long (5-s) light stimuli produces transient light responses (repolarization within ca. 200 ms) in an ICM containing only 10nM free Ca(2+). At 0.44 microM free Ca(2+) in the ICM, the microvillar membrane depolarizes by 10-20 mV and responses to 5-s light steps have an initial transient component and a plateau component, similar to responses in intact cells. Generation of the plateau compone...Continue Reading

References

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Jul 1, 1969·The Journal of Cell Biology·A Lasansky, M G Fuortes
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Feb 24, 2001·Journal of Comparative Physiology. A, Sensory, Neural, and Behavioral Physiology·B WalzB Zimmermann
Apr 6, 2001·Journal of Comparative Physiology. A, Sensory, Neural, and Behavioral Physiology·K Ukhanov, B Walz
Sep 3, 2002·The Journal of Physiology·Giuseppe PiccoliEnrico Nasi

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Citations

Feb 8, 2006·Annual Review of Physiology·Baruch Minke, Moshe Parnas

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