. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MYOGENIC ACTIVITY IX L1MVLUS HKART 271. FIGURE 2. Low calcium induced myogenic activity in deganglionated Limit/its hearts; intracellular activity from two different hearts (A and B) immersed in M NaCl. Note pacemaker potentials. Zero potential indicated; calibration: 20 tnv, 500 msec. Sodium chloride myogenicity When a Liiintlus heart was deganglionated, pinned out. and immersed in 600 HIM sodium chloride, rhythmic local contractions began rather suddenly within 10-20 min. This activity lasted longer than 30 minutes but
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. MYOGENIC ACTIVITY IX L1MVLUS HKART 271. FIGURE 2. Low calcium induced myogenic activity in deganglionated Limit/its hearts; intracellular activity from two different hearts (A and B) immersed in M NaCl. Note pacemaker potentials. Zero potential indicated; calibration: 20 tnv, 500 msec. Sodium chloride myogenicity When a Liiintlus heart was deganglionated, pinned out. and immersed in 600 HIM sodium chloride, rhythmic local contractions began rather suddenly within 10-20 min. This activity lasted longer than 30 minutes but was seldom sufficiently coordinated to result in a synchronous contraction of most or all of the heart. Impalement of muscle cells in spontaneously contracting segments revealed slowly depolarizing pacemaker potentials which induced rhythmic spiking activity (Fig. 2). Resting membrane potentials were 35-45 mv. Spikes were usually overshooting, and had long durations, never lasting less than 100 msec and often lasting several hundred msec. Often spikes of long duration and small amplitude were observed. Their slow7 rise time and diminished height suggested that they may have been decrementally conducted from a distant spiking site (see Rulon, Hermsmeyer and Sperelakis, 1971). The parameters of spike duration and spike height were variable from one recording site to another in a given heart as well as at a given recording site over short periods of time. In addition, two spikes were often recorded sequentially from a single fiber, each having unique parameters of duration and height (Fig. 2B). Spike height was dependent on external sodium ion concentration. In 444 HIM sodium chloride, the same concentration as found in Liniiiliis physiological solu- tion, spikes were never overshooting (Lang, 1970; Rulon, Hermsmeyer and Spere- lakis, 1970). Decreasing external sodium to 225-250 mM, and replacing with the osmotic equivalent of sucrose, resulted in a decrease in spike height to th
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
