Fig. 3

Cone I _Ca and its surround response recorded in a superfusate enriched with HEPES. A Effects of 10 mM HEPES-enriched buffer on cone I _Ca and surround response. The cone in newt retinal slice was depolarized from the holding voltage of −40 to −26 mV. Diffuse light illumination (4,000 μm in diameter used for surround illumination: shorter bar) was given during the step depolarization in the presence of a small spot light (30 μm in diameter: top bar). Changing the superfusate from control solution (black trace) to one supplemented with 10 mM HEPES increased cone I _Ca and prevented any additional inward current upon surround illumination (gray trace). Inset shows horizontal cell (HC) responses to a large light spot (4,000 μm in diameter) in the control solution and in the solution enriched with HEPES. B a Reversible effects of 10 mM HEPES-enriched buffer on cone I _Ca and surround response. The small spot light (30 μm in diameter: top bars) was kept on throughout. Diffuse light illumination (4,000 μm in diameter: shorter bar) was given during the step depolarization in the presence of the small spot. The cone was held at −40 mV and polarized to voltages ranging from −50 to +6 mV in 8 mV steps. The current traces before, during and after application of 10 mM HEPES-enriched buffer. The recording sequence was left column (−34, −18 and −10 mV) followed by the middle column and finally the right column. The leak conductance of 2.26 nS did not change either in the HEPES-containing solution or during the washout (current traces at −34 mV). In the HEPES-containing solution, inward I _Ca in darkness was reversibly increased, and the surround response was reversibly suppressed (current traces at −18 and −10 mV). Symbols denote the sampling points for calculation of the I–V curves of I _Ca in B b. In the control solution, the inward current produced by I _Ca was counterbalanced by the outward leak current (at −18 and −10 mV in the control and washout solutions). B b I–V curves of cone I _Ca recorded in B a. The leak conductance was subtracted. Filled and open squares in the control solution without and with surround illumination, respectively; filled and open gray circles in the HEPES-containing solution without and with surround illumination, respectively. Inset shows the voltage dependence of the surround response in the control solution (filled squares) and in the HEPES-containing solution (open circles). B c Activation curves fitted to the Boltzmann function derived from the data in B b (from Hirasawa and Kaneko [28])