Gc. Demontis et al., Properties and functional roles of hyperpolarization-gated currents in guinea-pig retinal rods, J PHYSL LON, 515(3), 1999, pp. 813-828
1. The inward rectification induced by membrane hyperpolarization was studi
ed in adult guinea-pig rods by the perforated-patch-clamp technique.
2. CsCl blocked the rectification observed in both voltage- and current-cla
mp recordings at voltages negative to -60 mV, while BaCl2, blocked the inwa
rd relaxation observed at voltages positive to -60 mV. The current activate
d at -90 mV had a low selectivity between sodium and potassium and reversed
at -31.0 mV.
3. These observations suggest that two inward rectifiers are present in gui
nea-pig rods: a hyperpolarization-activated (I-h) and a hyperpolarization-d
eactivated (I-kx) current. The functional roles of I-h and I-kx were evalua
ted bg stimulating rods with currents sinusoidally modulated in time.
4. Rods behave like bandpass amplifiers, with a peak amplification of 1.5 a
t about 2 Hz. For hyperpolarizations that mainly gate I-kx, amplification a
nd phase shifts are fully accounted for by a rod membrane analogue model th
at includes an inductance. For hyperpolarizations that also gate I-h, a har
monic distortion became apparent.
5. Bandpass filtering and amplification of rod signals, associated with I-h
and I-kx gating by membrane hyperpolarization, are strategically located t
o extend, beyond the limits imposed by the slow phototransductive cascade,
the temporal resolution of signals spreading to the rod synapse.