TY - JOUR T1 - Rapid Coupling of Calcium Release to Depolarization in<em>Limulus polyphemus</em> Ventral Photoreceptors as Revealed by Microphotolysis and Confocal Microscopy JF - The Journal of Neuroscience JO - J. Neurosci. SP - 1701 LP - 1709 DO - 10.1523/JNEUROSCI.17-05-01701.1997 VL - 17 IS - 5 AU - Kyrill Ukhanov AU - Richard Payne Y1 - 1997/03/01 UR - http://www.jneurosci.org/content/17/5/1701.abstract N2 - Microphotolysis and confocal microscopy were used to investigate the timing of calcium release and of the electrical response inLimulus polyphemus ventral photoreceptors. The fluorescent dyes Fluo-3 and Calcium Green-5N were used to monitor local Ca2+ elevations. Photolysis of caged inositol trisphosphate (InsP3) close to the plasma membrane of the light-sensitive rhabdomeral (R-) lobe resulted in Ca2+elevation within 10–20 msec, 20–45 msec before the physiological response to light normally would be detected. Inward ionic current flow and depolarization followed InsP3-induced calcium release within 2.5 ± 3.3 msec. Voltage-clamping the cells and removal of extracellular Ca2+ did not affect the timing of the Ca2+ elevation that followed the photolysis of caged InsP3 or its relationship to the electrical response. In contrast to the physiological response to light, which only released calcium within the R-lobe, photolysis of InsP3 elevated Cai in both lobes, although with much greater effect in the R-lobe, as compared with the bulk of the A-lobe, suggesting the presence of InsP3-sensitive calcium stores in both lobes. Photolysis of caged calcium [o-nitrophenyl EGTA (NPE)] at the edge of the R-lobe activated an inward ionic current within 1.8 ± 0.7 msec. This NPE-induced current reversed at a membrane potential of 10 ± 6 mV in the range typical of that of the light-activated current under physiological conditions. Calcium release, therefore, activates an inward current rapidly enough to contribute to the electrical response to light. ER -