. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 394 RALPH A. PAX AND RICHARD C. SANBORN for the regression line, is X lO8 M while at X 1O5 M 5-HT a relative heart rate of zero would he expected. The strength of heart heat also decreases when 5-HT is perfused through the isolated heart (Fig. 1). In Figure 3 the relationship between 5-HT concentration and relative contraction strength is plotted for 14 perfusions of 5-HT in nine differ- ent hearts. The calculated threshold concentration for strength changes is X 10~8 M, about the same as that calculated for rate
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 394 RALPH A. PAX AND RICHARD C. SANBORN for the regression line, is X lO8 M while at X 1O5 M 5-HT a relative heart rate of zero would he expected. The strength of heart heat also decreases when 5-HT is perfused through the isolated heart (Fig. 1). In Figure 3 the relationship between 5-HT concentration and relative contraction strength is plotted for 14 perfusions of 5-HT in nine differ- ent hearts. The calculated threshold concentration for strength changes is X 10~8 M, about the same as that calculated for rate changes, but the calculated regression lines for rate and strength changes are not parallel (slope = — for rate, — for strength). \0 \. $.0 10 23 60 100 S-HT (M X I0'r) FIGURE 3. Relation of relative contraction strength to concentration of 5-HT perfused through the isolated heart. Each point represents a single perfusion. The solid line is the regression line determined by the method of least squares and the dashed lines are the standard error of the regression line. Both of the above effects of 5-HT are readily reversible. Perfusion with drug- free saline for five minutes following drug treatment is usually sufficient to bring the rate and strength of beating within 10% of their pre-treatment levels. Neither 5-hydroxytryptophan—the precursor of 5-HT—nor 5-hydroxyindole- acetic acid—its major metabolite—at 10~4 M had any detectable effects on rate or strength of beating of the isolated heart. Electrical activity of the isolated cardiac ganglion is also affected by 5-HT treat- ment. The rate of rhythmic discharges decreases. The number of units discharging in each burst is reduced and the total duration of each burst is lessened. The pattern of a typical burst of electrical activity recorded from the fourth segment of the isolated cardiac ganglion before treatment and after treatment with 1 X 10~6 M 5-HT is shown in Figure 4. In this experiment
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
