The slow Ca[2[+]]-activated K[+] current found in photoreceptors is abolished in SK¹ mutants.

The current/voltage relationship of SK¹ photoreceptors is the same as in wild-type, exhibiting increased conductance with hyperpolarization. This current is not affected by tetraethylammonium application.

In dissociated photoreceptors, 1-Ethyl-2-benzimidazolinone induces a slow Ca[2[+]]-activated K[+] current in wild-type but not in SK¹ mutants. However the SK current is not altered by apamin treatment, suggesting that SK is apamin insensitive.

SK¹ mutant photoreceptors respond as wild-type to intensified light flashes, with graded transient depolarisation, covering similar ranges. However, SK¹ photoreceptors show accelerated kinetics; their responses reach peak amplitudes faster and recover to resting potential earlier.

SK¹ eyes consist of highly ordered ommatidia, with intact rhabdomeres, as in wild-type. However, prolonged light exposure results in minor changes in photoreceptor integrity. Bump waveforms in SK¹ photoreceptors are indistinguishable from those of wild-type photoreceptors. Macroscopic responses to increasing light intensities are similar in wild-type and mutant photoreceptors and share the same kinetics.

Compared with wild-type, SK¹ mutant photoreceptor cells exhibit an approximate 25% reduction inI[[A]] current but normal slow delayed rectifier (I[[KS]]) current.

The input resistance of dark-adapted SK¹ photoreceptors is significantly decreased compared to wild-type. This is accompanied by a more depolarized resting potential in the dark. Furthermore, in the dark, when their output shows no oscillations, SK¹ photoreceptors are noisier than their wild-type counterparts.

SK¹ photoreceptors exhibit reduced input resistance, elevated resting potential, and slow oscillating responses.

Although both wild-type and SK¹ large monopolar cells respond to light flashes with graded hyperpolarizations of similar sizes, the responses of mutant large monopolar cells are significantly faster. Approximately 40% of SK¹ mutant large monopolar cells show oscillating responses. The oscillations are exacerbated at dim conditions. Longer recordings reveal that the oscillations in mutant cells carry different frequencies during and after light adaption. Furthermore, compared with photoreceptors, these oscillations are larger and faster, peaking at ~100Hz.