Abstract
1. The light-dependent demolition of rhabdoms induced by a protein phosphatase inhibitor, okadaic acid (OKA) in retinas of a crab (Leptograpsus variegatus) is examined to determine whether the effects of OKA merely amplify the endocytosis of normal phototransductive membrane turnover, or are distinct from it. 2. OKA-induced demolition by ‘dawn’ retinas maintained in vitro is partially blocked by either of two protein kinase C inhibitors, staurosporine and H-7. It is similarly blocked by a Ca2+-channel blocking agent, diltiazem. 3. Large ‘night’ rhabdoms illuminated at 40 lux for up to 20 min are reduced by pinocytosis which is not inhibited by either staurosporine or diltiazem, each in the absence of OKA. 4. Pinocytosis is not blocked by a high concentration of a specific tyrosine kinase inhibitor, genistein in absence of OKA. 5. It is inferred that (i) phosphorylations of rhabdomeral proteins drive light-dependent, OKA-induced endocytosis; (ii) phosphorylations (including that of rhodopsin) do not drive normal, light-dependent endocytosis; (iii) tyrosine phosphorylations of a notional, minor population of rhabdomeral proteins are unlikely to determine, normal, light-dependent endocytosis of phototransductive membrane; (iv) entry of Ca2+ into R1-7 photoreceptors via either light-dependent or other channels is necessary for events provoked by OKA, but irrelevant to normal light-dependent endocytosis.
Published Version
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