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J. Zhang, S.M. Wu; Dual Voltage and Current Clamp Analysis of Physiological Properties of Cx35/36 –mediated Rod Photoreceptor Coupling in the Tiger Salamander Retina . Invest. Ophthalmol. Vis. Sci. 2004;45(13):1147.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Our previous study has suggested that Cx35/36 is the gap junction protein between rod photoreceptors in the tiger salamander retina. The objective of this study is to characterize the physiological properties of Cx35/36 gap junction proteins between rods and their functional roles in signal spread in the photoreceptor network. Methods: Dual whole–cell voltage and current clamp recordings were performed on pairs of rod photoreceptors in living retinal slices of the larval tiger salamander. Cell morphology and relative positions of the rod pairs were revealed by Lucifer yellow loaded through the two recording electrodes. Results: When two adjacent rods were held at –40mV, a voltage step series (from –120 to 100mV with an increment of 20mV) applied to one rod (driver cell) evoked current responses in the neighboring cell (follower cell) of opposite polarity to the responses in the driver cell. The maximum amplitude of the currents in the follower cell ranged from 30–300pA, and the current (in follower cell)–voltage (difference voltage) relations are approximately linear. Switching driver/follower cell positions generated identical responses, suggesting that rod–rod coupling is symmetrical. In the current clamp mode, a current step series (from –1000 to 1000pA with an increment of 150pA) applied to the driver cell evoked delayed voltage responses in the follower cell with the same polarity. The average coupling coefficient (ratio of the voltage change in the follower cell to that in the driver cell) was 0.11 ± 0.013. Signal transfer between rods was frequency dependent, and the electrical synapses act like a low–pass filter with an average cutoff frequency of 40±8 Hz. In the presence of 40mM TEA, which increased the input resistance of the rods and partially suppressed Ih, the current–voltage relation was linear and the evoked current responses remained symmetrical. The junctional conductance, coupling coefficient, and cut–off frequency under different adaptation conditions and in the presence of various gap junction regulators were studied. Conclusions: Our data suggest that the physiological properties of electrical synapses between salamander rod photoreceptors resemble those of the connexin 35/36 gap junction channels described in other parts of the nervous system. The current–voltage relation of the rod–rod gap junction is approximately linear and the evoked transjunctional current is symmetrical. Electrical synapses between rods act like low–pass filters with a cutoff frequency near 40 Hz.
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