j *@ - Sociedade Brasileira de Psicologia

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the reverse of adaptation, both must involve calcium . It lms been known for a long
time tbnt (1) ilumination incwre>sçs the ilmacelxlnr concentration of free caldlm
ions and (2) that amplitude an (i latency reduction œn be produce d b yinjecting
calcium into tle cels (Brown and Lismnn , 1975 ; Fein and Chadton, 1977). lf facilitation
is the reverse of adaptation, the rise in response should be accompanied by
lengthening of latency. But in our IRG work there was no systematic relationship
between facilitation and latency. Harmni (1986) also measlzred this relationship in
the barnacle photoreceptor w ih the fmding that latency ks not lçngthened , rather
it .is shortened during faciliation. He concluded that facilitation is not the result of
a reduction in intracelular calcillm concentration. We confirmed that latency is
constant and short despite increases in Amplitude of the facilitated responses in our
intracelular measurements (Ventura, 1988). Hanani's suggestion to explain facilitation
is that a Feater effecti#e light intensity exists during facilitation , leading to
greater nmplitude and sborter latency.
. A posibility we would like to consider is that this (suggested) increased
effectiveness of photoreceptor response be due to an increased amount of second
transmitter, such as CGMP or 1nsP3, both of wlzich have been proposed as messengers
for invertebrate photoreceptors ttx'lpb, 1986; Fein et al., 1984; Ventura, 1988). Since
a relationship between increased InsP3 content in the photoreceptor and increased
response to light has been shown tœ ul-y et al., 1987), this is a lead that should be
followed in future research.
References :
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photoreceptors. Nature 258 : 252-254, 1985. .
Da l, R.D. Facilitation in arthrotcpod photoreceptors . J. Gen. JWlafol. 71 : 221-222, 1978.
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