GtetP acts subsequent to Ca2+-mediated excitation. (A) Injection from a microelectrode containing 25 mM GtetP caused a progressive decline in the response to injection from a second microelectrode of 1.8 mM Ca2+ solution buffered with 2 mM HEDTA. Data points are the average response with error bars (std. dev.) to ten consecutive Ca2+ injections before, after inhibition of the light response by GtetP, and late in recovery of the light response. GtetP was injected during the period indicated by the bar positioned between the graphs. Brackets and arrows match response amplitude to averaged voltage time course in the insets. (B) GtetP injection inhibited the response to test flashes in parallel to the decline in response to Ca2+.