Figure 13. Quantum bumps in trp photoreceptors.

A, the membrane of a trp³⁰¹ photoreceptor was quiet in the dark (upper trace) but during dim illumination (lower trace), small, ca 2–3 pA, bumps were clearly distinguishable. Occasionally a larger bump similar in size to those recorded in WT was observed (start of trace). B, flash bumps elicited in a trp³⁴³ photoreceptor by a short (0.5 ms) flash (at times indicated by arrows) shown on a faster time scale. Most flashes elicited bumps of 2–4 pA, often with indications of repeated single or double channel openings (assuming single-channel currents of ca 2 pA); again occasional bumps of ca 10 pA were observed. C, amplitude histogram of quantum bumps determined from ca 90 ‘flash’ bumps in a trp³⁰¹ photoreceptor. There is a major peak at 3 pA, with a few (ca 5 %) outliers at around 10–11 pA, but with no indication of an intermediate peak. Amplitude was measured from the maximum current following the flash, and corrected for recording noise by subtracting the standard deviation of the current recorded in the dark immediately prior to the flash. Similar results were obtained in eight other cells in both trp³⁰¹ and trp³⁴³.