| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1994: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 1993: ¥1,100,000 (Direct Cost: ¥1,100,000)
|
|---|
| Research Abstract |
Now, a second messenger involved in phototransduction of invertebrate photoreceptors remains unclear. Then, the molecular mechanism mediating the depolarizing receptor potential of the extra-ocular photoreceptor cells, A-P-1 and Es-1 was examined. A-P-1 and Es-1, the photoresponsive neurons located within the mollusc, Onchidium ganglia are thought to be a primitive visual cell. Previous studies have shown that light depolarizes A-P-1 or Es-1 by suppressing the dark K^+ currents which are controlled by an internal messenger, cGMP.
In cell-attached patch recordings of A-P-1 or Es-1, single-channels which are active in the dark and closed by light (the light-sensitive channels)could be shown in the presence of external Ca^<2+> and Mg^<2+>. The reversal potential and its shift for the single-channel currents, measured with different K^+-filled patch pipettes showed that the light-sensitive channels were K^+-selective. The single-channel conductance was about 71 pS with 200 mM K^+ and about 100 pS with 450 mM K^+ in the pipettes, as determined from the slope of I-V relationship. Application of cGMP to excised inside-out patches activated (opened) a channel, equivalent to the light-sensitive channel recorded from the same membrane in the intact cell. Channel activation was dependent on the concentration of cGMP,and half-maximal activation occured between 20 and 100 muM cGMP.However, no channel activity was observed with application of cAMP of Ca^<2+> to the same patches in concentrations as high as 2 mM.Thus, we succeeded in clearing a new class of K^+ channel which is closed by light and is opened by cGMP in the Onchidium photoreceptor cells. Further, we are currently trying to clear immunocytochemical localization and chromatographic properties of photopigments in A-P-1 and Es-1.
|
