Protein kinase C activity and light sensitivity of dissociated salamander rods

Purpose. Biochemi cal experiments by others have indi cated that protei n kinäse C (PKC) activity is present in the rod outer segment, with potential or demonstrated targets including rhodopsin, transducin, the inhibitory subunit (PDEY) of the cGMPphosphodiesterase, guanylate cyclase and arrestin, which are all components of the phototransduction cascade. In particular, PKC phosphorylation of rhodopsin and PDEr have been studied in some detail, and suggested to have roles in down-regulating the sensitivity of rod photoreceptors to 1ight. We have addressed this question by recording electrophysiologically from single amphibian rods. Methods. We recorded from single, mechani call y di ssociated salamander rods by drawing its inner segment into a suction pipette while perfusing its outer segment with a bath solution containing a PKC activator or inhibitor. Results. We have tested three phorbol esters which activate PKC (PMA at 1 -4M, PDA at 20 i-4M, PDBu at 20 nM), as well as the PKC inhibitor GF109203X (1 nM), on the flash sensitivity of the dissociated rods under three conditions: 1) in darkness, 2) in the presence of a steady, non-saturating light, and 3) duri ng the recovery phase in darkness after a ca. 1% bleach. In all cases where a chemical was present, the rod sensitivity was either unchanged or only slightly different from control. Conclusions. PKC perhaps does not have an important role in the regulation of 1ight sensitivity, at least for isolated amphibian rods.