Figure 4.

Dorsal vessel contraction is reduced in Ryr¹⁶ and ryanodine-treated larvae. (A) GFP is expressed in all muscles of a wild type, second instar larvae (see Fig. 2). (B) The cardial cells of the heart are shown at higher magnification with the dorsal vessel in the closed position. (Scale bars in A and B, 10 μm.) (C) Heart rate was measured by counting the number of beats per minute for a population of each larval genotype. There was no significant difference between the heart rate of wild-type (second instar) and Ryr¹⁶/CyO (first instar) larvae. Both Ryr¹⁶ larvae and second instar larvae treated with 100 μM ryanodine, however, showed a marked reduction in the rate of contraction. Heart rates were measured for each genotype in at least three independent experiments (n ≥ 15), and the error is the SEM.