Voltage-activated potassium channels in the plasma membrane of rod outer segments: a possible effect of enzymatic cell dissociation.

Using patch-clamp techniques, we recorded single-channel currents from the plasma membrane of the outer segment of isolated light-adapted rods. The channels are potassium-selective and their conductance is about 87 pS. The channels are activated by depolarization and are not sensitive to cytoplasmic calcium, they are exclusively found in rods isolated with the proteolytic enzyme papain, and are not detected in rods isolated by mechanical means. Thus, these channels do not exist in an activatable form in the outer segment plasma membrane under physiological conditions. The channels might be derived from a normally inaccessible structure, such as the disk membrane, or, alternatively, they might be a modified form of a channel that is not active in the intact rod.